ATerm Library User Manual - The Meta

ATerm Library User Manual - The Meta
ATerm Library User Manual
Hayco de Jong
Pieter Olivier
Centrum voor Wiskunde en Informatica (CWI),
Kruislaan 413, 1098 SJ Amsterdam, The Netherlands
E-mail: [email protected] - [email protected]
Abstract
This report is a manual describing the functionality provided by the ATerm Library, a high performance implementation of the ATerm datatype using maximal sharing and automatic garbage collection.
Contents
1 Introduction
3
2 Using the ATerm Library
2.1 Maximal sharing . . . . . . . . . . . . . . . .
2.2 Garbage collector . . . . . . . . . . . . . . . .
2.3 Initialising the ATerm Library . . . . . . . . .
2.4 Protecting global ATerms and arrays of ATerms
2.5 Unprotecting protected ATerms . . . . . . . . .
2.6 Binary ATerm Format (BAF) . . . . . . . . . .
2.7 Shared Textual ATerm Format (TAF) . . . . . .
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3
3
4
4
4
5
5
5
3 Level One Interface
3.1 Level One Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 A note on ‘blobs’ and BAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Level One Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
6
6
6
4 Level Two Interface
4.1 Level Two Types . . . . .
4.2 Level Two Functionality .
4.2.1 ATermInt . . . . .
4.2.2 ATermReal . . . .
4.2.3 ATermAppl . . . .
4.2.4 ATermList . . . .
4.2.5 ATermPlaceholder
4.2.6 ATermBlob . . . .
4.3 Dictionaries . . . . . . . .
4.4 Tables . . . . . . . . . . .
4.5 Indexed sets . . . . . . . .
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13
13
13
13
14
14
16
21
22
22
23
24
5 Utilities
5.1 ATerm-conversion: baffle . . . . . . . . . . . . . .
5.2 Calculating an ATerm’s size: termsize . . . . . . .
5.3 Calculating MD5 checksum of an ATerm: atsum . . .
5.4 Calculating differences between two ATerms: atdiff
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Index
25
25
26
26
26
27
A The ToolBus layer
A.1 Generation of tool interfaces . . . . . . . .
A.2 Example . . . . . . . . . . . . . . . . . . .
A.3 Functions in the ToolBus layer . . . . . .
A.4 Control flow without the ATBeventloop
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29
29
29
32
33
B Java implementation
B.1 Interfaces and Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B.2 Class hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
34
35
C Connecting Java tools
35
2
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1 Introduction
This manual describes the functionality provided by the ATerm Library. The library is a high performance
implementation of the ATerm datatype described in [BJKO00]. If your application satisfies the following
list of characteristics, the ATerm Library can probably prove to be a valuable component.
• Maximal sharing of terms is required;
• Automatic garbage collection is required;
• There is no need for destructive update of terms (the ATerm Library is not suited to implement e.g.
stacks).
Typical applications that benefit from using the ATerm Library are those that manipulate (abstract
syntax) trees or terms, and those that are related to the new A SF +S DF Meta-Environment [BKMO97] or
the new A SF +S DF compiler [BOHK98].
This manual is intended to be a comprehensive text on how to use the ATerm Library. Readers who are
interested in the design details of the ATerm Library, can find these in [BJKO00].
Section 2 explains the basic steps that must be taken to initialise and work with the ATerm Library.
The level one interface described in Section 3 offers a set of operations on ATerms that is sufficiently
powerful for most users, yet is concise enough to be mastered in a relatively short period of time.
Section 4 describes the level two interface which is intented for experienced ATerm users, providing a
more extensive set of datastructures and functions.
The ATerm Library comes with a number of utility programs. A description of these programs can be
found in Section 5.
2 Using the ATerm Library
This section explains the basics of using the ATerm Library. One design decision, basing the ATerm Library
on maximally shared ATerms, has some consequences that readers should be familiar with before using the
ATerm Library. Section 2.1 therefore addresses the notion of maximal sharing and its consequences on the
use of ATerms.
The ATerm Library has a built-in garbage collector. Section 2.2 explains what this garbage collector
does and when it is invoked.
To use the ATerm Library, it must first be initialised. This ensures that the garbage collector is activated
and that all necessary internal structures are set up. Section 2.3 demonstrates initialisation of the ATerm
Library and shows all possible commandline options. These alter the behaviour of the ATerm Library.
The garbage collector detects references to ATerms that are on the stack and in any of the registers.
As it is also possible to have global references to ATerms which the garbage collector cannot detect, it is
the user’s responsibility to protect these references from premature erasure. Section 2.4 explains how to
protect global ATerm variables and arrays of ATerms.
The ATerm Library is capable of storing ATerms in a compact, portable binary notation. Section 2.6
describes this binary ATerm format.
2.1 Maximal sharing
Although explaining the design details of the ATerm Library is beyond the scope of this manual, it is
important that users realise that the ATerm Library is implemented using maximally shared ATerms. This
means that before a new ATerm is created, a lookup is done to see if that term already exists. If so, that
term is reused and no new term is created, resulting in maximally shared terms. This has the advantage
that equality of terms can be expressed as being physically the same term, i.e., both terms must have the
same memory address. It also means that, as terms can be shared without the user knowing it, they cannot
be modified without creating unwanted side effects. Thus, users should not tamper with ATerms. Rather,
they should use the functionality provided in the level one and level two interfaces.
3
2.2 Garbage collector
The ATerm Library uses garbage collection to find and delete unused ATerms. This relieves users of the
burden of explicitly allocating and freeing every ATerm used in an application. Each time a new ATerm
is allocated the garbage collector decides whether time has come to free resources claimed by unused
ATerms or whether there still is enough space to create the requested term. Details on the design and
implementation of this garbage collection can be found in [BJKO00].
2.3 Initialising the ATerm Library
To initialise the ATerm Library, a call to ATinit must be made from main, passing the commandline
arguments stored in argc and argv. The address of a locally created ATerm variable must also be passed.
This address is used by the garbage collector to determine the bottom of the stack to be inspected for
ATerms. The following code demonstrates a typical initialisation of the ATerm Library.
#include <stdio.h>
#include <aterm1.h>
int main(int argc, char *argv[])
{
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
foo();
return 0;
}
/*
/*
/*
/*
Used in initialisation of library
*/
Initialise the ATerm library.
*/
Call to code that works with ATerms. */
End of program. */
The following commandline options can be passed to the ATerm Library:
-at-symboltable <nr symbols>
-at-termtable <table class>
-at-hashinfo
-at-print-gc-time
-at-print-gc-info
-at-silent
Initial size of symboltable
Start with termtable of 2table class entries
write hashtable statistics to hashing.stats
after execution
print timing information about garbage collector
to stderr after execution
print verbose information about garbage collector
to stderr after execution
Do not print status and version information
2.4 Protecting global ATerms and arrays of ATerms
During a garbage collect, the ATerm Library searches the stack and registers for ATerms. Therefore it
finds all ATerms which were created locally in a function (automatic variables). All ATerm variables
which were not created locally, must be protected by a call to ATprotect. For entire arrays of ATerms,
ATprotectArray should be used. Note that not the ATerm variable itself, but its address is passed to
ATprotect. Users of the level two interface who create a function application by building the function
symbol (AFun) can also keep global references to these symbols. Such references should be protected
through a call to ATprotectAFun.
The following code demonstrates the protection of a global ATerm and a global array of ATerms.
#include <stdio.h>
#include <aterm1.h>
static ATerm global_aterm;
/* global ATerm */
4
#define NR_ENTRIES 42
static ATerm global_arr[NR_ENTRIES];
/* arbitrary number for this example. */
/* global ATerm array. */
int main(int argc, char *argv[])
{
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
ATprotect(&global_aterm);
ATprotectArray(global_arr, NR_ENTRIES);
foo();
/* Used in initialisation of library
*/
/*
/*
/*
/*
*/
*/
*/
*/
Initialise the ATerm library.
Protect the global aterm variable.
Protect the global aterm array.
Call to code that works with ATerms.
/* End of program. */
return 0;
}
2.5 Unprotecting protected ATerms
When the lifetime of an ATerm that was protected as described in Section 2.4 has expired, the ATerm
should be unprotected to free any internal resources it holds. Note that these resources are not released
immediately. Instead, they are no longer marked as protected to the garbage collector and as such may be
freed at the next garbage collection. For each ATprotect function, there is a matching ATunprotect
function.
2.6 Binary ATerm Format (BAF)
In addition to being able to parse terms in textual format and write textual representations of ATerms, the
ATerm Library is also equipped to store and restore ATerms in a compact, portable binary representation.
This representation is called BAF which stands for “Binary ATerm Format”.
This format can be used to write a binary version of an ATerm to file, which can later be restored in a
much more efficient way than would be possible had the ATerm’s textual counterpart been used. This is
due to the fact that textual representations have to be (re-)parsed each time they are read from file, whereas
BAF directly describes how to rebuild the internal representation of an ATerm, thus skipping the parsing
phase. Moreover, the maximal sharing of ATerms is exploited when writing BAF-representations, making
them take up much less space than their textual representations would have needed.
Users of the ATerm Library are encouraged to use BAF representations when saving ATerms to file. BAF
was designed to be platform independent, which facilitates the exchange of ATerms. The ATerm Library
comes with a utility that is able to convert an ATerm’s textual representation into its BAF counterpart and
vice versa (see Section 5.1). This conversion makes it possible to always work with BAF representations,
while still being able to look at the textual representation any time an error is suspected. It also allows
conversion of textual ATerms written by programs unable to write BAF which is especially convenient
when these ATerms are bulky.
Although the ATerm Library does not put any constraints on the names of ATerm-files, users are encouraged to use the extension .baf for BAF files. This will avoid confusion between textual representations
and binary ones. Textual representations could use the extension .trm.
2.7 Shared Textual ATerm Format (TAF)
In addition to the binary aterm format there is also a textual aterm format which supports maximal sharing
but uses a much less complex algorithm than the one used to encode and decode BAF files. This results in
files that are somewhat larger than their baf counterparts, but are often (if the terms contain redundancy)
significantly smaller than their unparsed form.
5
TAF files always start with a ’!’ character to distinguish them from aterm formats. The format uses abbreviations to refer to previously written terms. An abbreviation consists of a hash character (’#’) followed
by a number in encoded using the Base64 Alphabet (see RFC2045).
Each term whose unparsed representation would take up more bytes than the textual representation
of the next available abbreviation is assigned such an abbreviation after it has been written. Subsequent
occurences of this term are then written by emitting the abbreviation instead of the term itself.
For example the term f(test,test) is represented as !f(test,#A) in TAF, whereas f(a,a) is
respresented as !f(a,a) because test is longer than its abbreviation #A, but a is not.
3 Level One Interface
This section explains in detail the types and functions that are defined in the level one interface. These
functions are declared in aterm1.h. Section 3.1 reveals the types of ATerms that are used in the ATerm
Library, as well as the extension to the standard C-types introduced in the level one interface. To avoid
confusion between BAF and the ATerm type blob, Section 3.2 is dedicated to explaining the difference
between these two notions. Finally, Section 3.3 describes all the functions that are available in the level
one interface.
3.1 Level One Types
The following C-defines are used to represent the different ATerm types:
• AT FREE: An ATerm that is marked free will be reused when needed. This is not a type users will want to create
themselves, but it can be used to detect an ATerm that has been freed by the garbage collector.
• AT APPL: An ATerm of type: function application;
• AT INT: An ATerm of type: integer;
• AT REAL: An ATerm of type: real;
• AT LIST: An ATerm of type: list;
• AT PLACEHOLDER: An ATerm of type: placeholder;
• AT BLOB: An ATerm of type: binary large object;
The following C-types are defined in the level one interface:
• ATbool: a boolean value, either ATtrue or ATfalse;
• ATerm: an annotated term.
3.2 A note on ‘blobs’ and BAF
Please note that although the word binary is used in the abbreviations of both “blob” and BAF, these are
two very different notions. A blob represents an ATerm that holds binary data, with no specific meaning to
the ATerm Library. This notion can be used as a means of escape in case you find that you need a type of
ATerm that is not on the list above. The notion of BAF is explained in Section 2.6 and refers to a specific
format used for reading and writing ATerms. Thus an ATerm of type AT BLOB can be saved in BAF. It
could also be written in its textual representation, although this does not guarantee that the blob will be
readable, after all it represents binary data.
3.3 Level One Functionality
In this section, all functions and macros (#define’s in C) are listed. Although all macros could have been
implemented as a function as well, the macros listed here were chosen to be macros instead of functions
for efficiency reasons. To obtain access to the level one interface, your application should #include
<aterm1.h>.
6
function: ATmake
Summary: Create an ATerm from a string pattern and a variable number of arguments
Declaration: ATerm ATmake(const char *pattern, ...);
Description: Creates an ATerm given a pattern and corresponding values. The following table shows
which patterns can be used, and which type of arguments should be passed if such a pattern is used.
Type
Application
Blob
Integer
List
Placeholder
Real
String
Term
Pattern
<appl>
<blob>
<int>
<list>
<placeholder>
<real>
<str>
<term>
Argument
char *pattern, arguments
int length, void *data
int value
ATerm
char *type
double value
char *pattern, arguments
ATerm
Types <appl> and <str> should contain a pattern consisting of the function symbol to be used and the
types of the arguments. This pattern must be followed by exactly the number of arguments that are used in
the pattern. The types of the arguments must match the respective types used in the pattern. Both <appl>
and <str> create function applications. The difference is that <appl> creates one with an unquoted
function symbol, whereas <str> yields a quoted version.
Here are some examples of ATmake:
#include <aterm2.h>
int
ival
char *sval
char *blob
double rval
char *func
=
=
=
=
=
42;
"example";
"12345678";
3.14;
"f";
void foo()
{
ATerm term[4];
ATerm list[3];
ATerm appl[3];
term[0]
term[1]
term[2]
term[3]
=
=
=
=
ATmake("<int>" ,
ATmake("<str>" ,
ATmake("<real>",
ATmake("<blob>",
ival);
func);
rval);
8, blob);
/*
/*
/*
/*
integer value: 42
quoted application: "f", no args
real value: 3.14
blob of size 8, data: 12345678
*/
*/
*/
*/
list[0] = ATmake("[]");
list[1] = ATmake("[1,<int>,<real>]", ival, rval);
list[2] = ATmake("[<int>,<list>]", ival+1, list[1]);
appl[0] = ATmake("<appl>", func);
appl[1] = ATmake("<appl(<int>)>", func, ival);
appl[2] = ATmake("<appl(<int>, <term>, <list>)>", func, 42, term[3], list[2]);
ATprintf("appl[2] = %t\n", appl[2]);
}
int main(int argc, char *argv[])
{
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
7
foo();
return 0;
}
function: ATvmake
Summary: Create an ATerm from a string pattern and a list of arguments
Declaration: ATerm ATvmake(const char *pattern, va list args);
Description: See ATmake.
function: ATmakeTerm
Summary: Create an ATerm from an ATerm pattern and a variable number of arguments
Declaration: ATerm ATmakeTerm(ATerm pat, ...);
Description: See ATmake.
function: ATvmakeTerm
Summary: Create an ATerm from an ATerm pattern and a list of arguments
Declaration: ATerm ATvmakeTerm(ATerm pat, va list args);
Description: See ATmake.
function: ATmatch
Summary: Match an ATerm against a pattern
Declaration: ATbool ATmatch(ATerm t, const char *pattern, ...);
Description: Matches an ATerm against a pattern, attempting to fill the ‘holes’. If the ATerm matches the
pattern, ATtrue is returned and the variables will be filled according to the pattern, otherwise ATfalse
is returned.
The <list> pattern can be used to match the tail of a list as well as a variable number of arguments
in a function application. Thus the first few arguments may be matched explicitly while the tail of the
arguments is directed to a list.
Here are a few examples of ATmatch:
#include <aterm2.h>
void foo()
{
ATbool
ATerm
double
int
result;
list;
rval;
ival;
/* Sets result to ATtrue and ival to 16. */
result = ATmatch(ATmake("f(16)"), "f(<int>)", &ival);
/* Sets result to ATtrue and rval to 3.14. */
result = ATmatch(ATmake("3.14"), "<real>", &rval);
/* Sets result to ATfalse because f(g) != g(f) */
result = ATmatch(ATmake("f(g)"), "g(f)");
/* fills ival with 1 and list with [2,3] */
result = ATmatch(ATmake("[1,2,3]"), "[<int>,<list>]", &ival, &list);
}
int main(int argc, char *argv[])
8
{
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
foo();
return 0;
}
function: ATreadFromString
Summary: Read an ATerm from string
Declaration: ATerm ATreadFromString(const char *string);
Description: This function parses a character string into an ATerm. A convenience macro ATparse is
included in aterm1.h.
function: ATreadFromBinaryString
Summary: Read a ATerm from a string in BAF format.
Declaration: ATerm ATreadFromBinaryString(const char *string, int size);
Description: This function decodes a BAF character string into an ATerm.
function: ATreadFromSharedString
Summary: Read a ATerm from a string in TAF format.
Declaration: ATerm ATreadFromSharedString(const char *string, int size);
Description: This function decodes a TAF character string into an ATerm.
function: ATreadFromTextFile
Summary: Read an ATerm from text file
Declaration: ATerm ATreadFromTextFile(FILE *file);
Description: This function reads a text file and parses the contents into an ATerm.
function: ATreadFromBinaryFile
Summary: Read an ATerm from binary file (BAF)
Declaration: ATerm ATreadFromBinaryFile(FILE *file);
Description: This function reads a binary file and builds an ATerm.
function: ATreadFromSharedTextFile
Summary: Read an ATerm from a shared text file (TAF)
Declaration: ATerm ATreadFromSharedTextFile(FILE *file);
Description: This function reads a shared text file and buils an ATerm.
function: ATreadFromFile
Summary: Read an ATerm from binary or text file
Declaration: ATerm ATreadFromFile(FILE *file);
Description: This function reads an ATerm from a file. A test is performed to see if the file is in
TAF , or plain text.
BAF ,
function: ATreadFromNamedFile
Summary: Read an ATerm from named binary or text file
Declaration: ATerm ATreadFromNamedFile(char *filename);
Description: This function reads an ATerm file filename. A test is performed to see if the file is in
BAF , TAF , or plain text. ”-” is standard input’s filename.
9
macro: ATparse
Summary: A convenience macro for ATreadFromString
Declaration: ATerm ATparse(const char *str)
Description: This macro is simply a shortcut to ATreadFromString(str).
macro: ATgetType
Summary: Return the type of term
Declaration: int ATgetType(ATerm term)
Description: A macro that returns the type of an ATerm. Result is one of AT APPL, AT INT, AT REAL,
AT LIST, AT PLACEHOLDER, or AT BLOB.
macro: ATisEqual
Summary: A macro that tests equality of ATerms t1 and t2
Declaration: int ATisEqual(ATerm t1, ATerm t2)
Description: As ATerms are created using maximal sharing (see Section 2.1), testing equality is performed in constant time by comparing the addresses of t1 and t2. Note however that ATisEqual only
returns ATtrue when t1 and t2 are completely equal, inclusive any annotations they might have!
function: ATwriteToTextFile
Summary: Writes term t to file f in textual format
Declaration: ATbool ATwriteToTextFile(ATerm t, FILE *f);
Description: This function writes ATerm t to the file f in textual format. This term can later be read
again by ATreadFromTextFile.
function: ATwriteToSharedTextFile
Summary: Writes term t to file f in shared Textual ATerm Format (TAF)
Declaration: long ATwriteToSharedTextFile(ATerm t, FILE *f);
Description: This function writes ATerm t to the file f in TAF, and returns the number of characters
written. This term can later be read again by ATreadFromSharedTextFile.
function: ATwriteToBinaryFile
Summary: Writes term t to file f in Binary ATerm Format (BAF)
Declaration: ATbool ATwriteToBinaryFile(ATerm t, FILE *F);
Description: This function writes ATerm t to the file f in BAF. This term can later be read again by
ATreadFromBinaryFile.
function: ATWriteToNamedTextFile
Summary: Writes term t to file named filename in textual format
Declaration: ATerm ATWriteToNamedTextFile(ATerm t, char *filename);
Description: This function writes ATerm t in textual representation to file filename. ”-” is standard
output’s filename.
function: ATWriteToNamedBinaryFile
Summary: Writes term t to file named filename in Binary ATerm Format (BAF)
Declaration: ATerm ATWriteToNamedBinaryFile(ATerm t, char *filename);
Description: This function writes ATerm t in textual representation to file filename. ”-” is standard
output’s filename.
function: ATwriteToString
Summary: Writes term t to a string
Declaration: char * ATwriteToString(ATerm t);
Description: Writes term t to an internal string buffer. The start of this buffer is returned. Note that the
contents of this buffer are volatile and may be overwritten by any call to the ATerm Library.
10
function: ATwriteToSharedString
Summary: Writes term t to a shared text string in TAF
Declaration: char * ATwriteToSharedString(ATerm t, int *len);
Description: Writes term t to an internal string buffer in TAF. The start of this buffer is returned, and the
length of the resulting string is stored in len. Note that the contents of this buffer are volatile and may be
overwritten by any call to the ATerm Library.
function: ATwriteToBinaryString
Summary: Writes term t to a shared text string in BAF
Declaration: char * ATwriteToBinaryString(ATerm t, int *len);
Description: Writes term t to an internal string buffer in BAF. The start of this buffer is returned, and the
length of the resulting string is stored in len. Note that the contents of this buffer are volatile and may be
overwritten by any call to the ATerm Library.
function: ATsetAnnotation
Summary: Annotate a term with a labeled annotation
Declaration: ATerm ATsetAnnotation(ATerm t, ATerm label, ATerm anno);
Description: Creates a version of t that is annotated with annotation anno which is labeled by label.
function: ATgetAnnotation
Summary: Retrieves annotation of t with label label
Declaration: ATerm ATgetAnnotation(ATerm t, ATerm label);
Description: This function can be used to retrieve a specific annotation of a term. If t has no annotations,
or no annotation labeled with label exists, NULL is returned. Otherwise the annotation is returned.
function: ATremoveAnnotation
Summary: Remove a specific annotation from a term
Declaration: ATerm ATremoveAnnotation(ATerm t, ATerm label);
Description: This function returns a version of t which has its annotation with label label removed. If
t has no annotations, or no annotation labeled with label exists, t itself is returned.
function: ATinit
Summary: Initialise the ATerm Library.
Declaration: void ATinit(int argc, char *argv[], ATerm *bottomOfStack);
Description: See Section 2.3.
function: ATprintf
Summary: ATerm version of printf
Declaration: int ATprintf(const char *format, ...);
Description: See ATvfprintf.
function: ATfprintf
Summary: ATerm version of fprintf
Declaration: int ATfprintf(FILE *stream, const char *format, ...);
Description: See ATvfprintf.
function: ATvfprintf
Summary: ATerm version of vfprintf
Declaration: int ATvfprintf(FILE *stream, const char *format, va list args);
Description: The functions ATprintf, ATfprintf and ATvfprintf are used for formatted output to file. The conversion specifiers c, d, i, o, u, x, X, e, E, f, g, G, p, s behave
as can be expected from (f)printf. In addition the conversion specifiers a, h, l, n and t are
supported:
11
Conversion specifier
a
h
l
n
t
Action
print the symbol of an ATerm-application
print the MD5 checksum of an ATerm
print an ATerm-list
print information about an ATerm node
print an ATerm
function: ATsetWarningHandler
Summary: Specify a warninghandler for the ATerm Library
Declaration: void ATsetWarningHandler((void (*handler)(const char *, va list)));
Description: Sets a warninghandler for the ATerm Library. This handler will be called when an error
message is sent to ATwarning.
function: ATwarning
Summary: Issue a warning message
Declaration: void ATwarning((const char *format, ...));
Description: If an errorhandler has been installed through a call to ATsetWarningHandler, this handler will be called. Otherwise ATwarning uses ATvfprintf to print a formatted message to stderr
and returns.
function: ATsetErrorHandler
Summary: Specify an errorhandler for the ATerm Library
Declaration: void ATsetErrorHandler((void (*handler)(const char *, va list)));
Description: Sets an errorhandler for the ATerm Library. This handler will be called when an error
message is sent to ATerror.
function: ATerror
Summary: Issue an errormessage and exit the ATerm Library
Declaration: void ATerror((const char *format, ...));
Description: If an errorhandler has been installed through a call to ATsetErrorHandler, this handler
will be called. Otherwise ATerror uses ATvfprintf to print a formatted message to stderr and
exits with errorcode 1.
function: ATsetAbortHandler
Summary: Specify an aborthandler for the ATerm Library
Declaration: void ATsetAbortHandler((void (*handler)(const char *, va list)));
Description: Sets an aborthandler for the ATerm Library. This handler will be called when an error
message is sent to ATabort.
function: ATabort
Summary: Issue an errormessage and abort the ATerm Library
Declaration: void ATabort((const char *format, ...));
Description: If an aborthandler has been installed through a call to ATsetAbortHandler, this handler
will be called. Otherwise ATabort uses ATvfprintf to print a formatted message to stderr calls
abort.
function: ATprotect
Summary: Protect an ATerm
Declaration: void ATprotect(ATerm *atp);
Description: Protects an ATerm from being freed at garbage collection. See Section 2.4.
12
function: ATunprotect
Summary: Unprotect an ATerm
Declaration: void ATunprotect(ATerm *atp);
Description: Releases protection of an ATerm which has previously been protected through a call to
ATprotect. See Section 2.5.
function: ATprotectArray
Summary: Protect an array of ATerms
Declaration: void ATprotectArray(ATerm *start, int size));
Description: Protects an entire array of size ATerms starting at start.
function: ATunprotectArray
Summary: Unprotect an array of ATerms
Declaration: void ATunprotectArray(ATerm *start));
Description: Releases protection of the array of ATerms which starts at start.
4 Level Two Interface
This section explains in detail the types and functions that are defined in the level two interface. These
functions are declared in aterm2.h
4.1 Level Two Types
In addition to the C-types explained in Section 3.1, the level two interface also uses the following types:
• ATermInt: an integer value;
• ATermReal: a real value;
• ATermAppl: a function application;
• ATermList: a list;
• ATermPlaceholder: a placeholder;
• ATermBlob: a Binary Large OBject;
• ATermTable: a hashtable of ATerms;
• ATermIndexedSet: a set of ATermswhere each element has a unique index.
4.2 Level Two Functionality
This section describes all functions and macros that are available in the level two interface. To obtain access
to this functionality you need to #include <aterm2.h> instead of <aterm1.h> in your application.
In Section 3.3 we explained that the macros used in the level one interface could just as well have been
implemented as functions, but were chosen to be implemented as macros for efficiency reasons. The same
goes for all macros described in this section.
4.2.1 ATermInt
The type ATermInt is the ATerm representation of an integer. It abides by the rules of the C-type: int.
function: ATmakeInt
Summary: Build an ATermInt from an integer (int)
Declaration: ATermInt ATmakeInt(int value);
13
macro: ATgetInt
Summary: Get the integer value from an ATermInt.
Declaration: int ATgetInt(ATermInt t)
4.2.2 ATermReal
The type ATermReal is the ATerm representation of a real. It abides by the rules of the C-type: double.
function: ATmakeReal
Summary: Build an ATermReal from a real (double).
Declaration: ATermReal ATmakeReal(double value);
macro: ATgetReal
Summary: Macro to get the real value from an ATermReal.
Declaration: double ATgetReal(ATerm t)
4.2.3 ATermAppl
The type ATermAppl denotes a function application. In order to build a function application, first its
function symbol (AFun) must be built. This symbol holds the name of the function application, its arity
(how many arguments the function has) and whether the function name is quoted. Below are some examples
of function applications and the symbols needed to create them.
true
- a zero arity, unquoted function application
sym = ATmakeAFun("true", 0, ATfalse);
"true"
- the same function application, but quoted
sym = ATmakeAFun("true", 0, ATtrue);
f(0)
- an unquoted function application of arity 1
sym = ATmakeAFun("f", 1, ATfalse);
"prod"(2, b, [])
- a quoted function application of arity 3
sym = ATmakeAFun("prod", 3, ATtrue);
function: ATmakeAFun
Summary: Create a function symbol (AFun)
Declaration: AFun ATmakeAFun(char *name, int arity, ATbool quoted);
Description: Creates an AFun, representing a function symbol with name name and arity arity. Quotedness is passed through the quoted argument.
function: ATprotectAFun
Summary: Protect a function symbol
Declaration: void ATprotectAFun(AFun sym);
Description: Just as ATerms which are not on the stack or in registers must be protected through a call to
ATprotect, so must AFuns be protected by calling ATprotectAFun.
function: ATunprotectAFun
Summary: Release an AFun’s protection.
Declaration: void ATunprotectAFun(AFun sym);
macro: ATgetName
Summary: Return the name of an AFun
Declaration: char * ATgetName(AFun sym) .
14
macro: ATgetArity
Summary: Return the arity (number of arguments) of a function symbol (AFun)
Declaration: int ATgetArity(AFun sym)
macro: ATisQuoted
Summary: Determine if a function symbol (AFun) is quoted or not
Declaration: ATbool ATisQuoted(AFun sym)
function: ATmakeAppl
Summary: Build an application from an AFun and a variable number of arguments.
Declaration: ATermAppl ATmakeAppl(AFun sym, ...);
Description: The arity is taken from the first argument sym, the other arguments to ATmakeAppl should
be the arguments for the application. For arity 0 . . . 6 the corresponding ATmakeAppl<N> can be used
instead for greater efficiency.
function: ATmakeAppl0
Summary: Make a function application with zero arguments
Declaration: ATermAppl ATmakeAppl0(AFun s);
function: ATmakeAppl1
Summary: Make a function application with one argument
Declaration: ATermAppl ATmakeAppl1(AFun s, ATerm a0);
function: ATmakeAppl2
Summary: Make a function application with two arguments
Declaration: ATermAppl ATmakeAppl2(AFun s, ATerm a0, a1);
function: ATmakeAppl3
Summary: Make a function application with three arguments
Declaration: ATermAppl ATmakeAppl3(AFun s, ATerm a0, a1, a2);
function: ATmakeAppl4
Summary: Make a function application with four arguments
Declaration: ATermAppl ATmakeAppl4(AFun s, ATerm a0, a1, a2, a3);
function: ATmakeAppl5
Summary: Make a function application with five arguments
Declaration: ATermAppl ATmakeAppl5(AFun s, ATerm a0, a1, a2, a3, a4);
function: ATmakeAppl6
Summary: Make a function application with six arguments
Declaration: ATermAppl ATmakeAppl6(AFun s, ATerm a0, a1, a2, a3, a4, a5);
Description: These functions build an application of arity zero through six, i.e. an application with
0 . . . 6 arguments. Use these functions to build ATermAppls with small arity in favour of the generic
ATmakeAppl described above.
macro: ATgetAFun
Summary: Get the function symbol (AFun) of an application
Declaration: AFun ATgetAFun(ATermAppl appl)
macro: ATgetArgument
Summary: Get the nr-th argument of an application
Declaration: ATerm ATgetArgument(ATermAppl appl, int nr)
15
function: ATsetArgument
Summary: Set the nr-th argument of an application to arg
Declaration: ATermAppl ATsetArgument(ATermAppl appl, ATerm arg, int n);
Description: This function returns a copy of appl with argument n replaced by arg.
function: ATgetArguments
Summary: Get a list of arguments of an application
Declaration: ATermList ATgetArguments(ATermAppl appl);
Description: Return the arguments of appl in ATermList format. Note: traversing the arguments of
appl can be done more efficiently using the ATgetArgument macro.
function: ATmakeApplList
Summary: Build an application given an AFun and a list of arguments
Declaration: ATermAppl ATmakeApplList(AFun sym, ATermList args);
Description: Build an application from sym and the argument list args. Note: unless the arguments are
already in an ATermList, it is probably more efficient to use the appropriate ATmakeAppl<N>.
function: ATmakeApplArray
Summary: Build an application given an AFun and an array of arguments
Declaration: ATermAppl ATmakeApplArray(AFun sym, ATerm args[]);
4.2.4 ATermList
function: ATmakeList
Summary: Create an ATermList of n elements
Declaration: ATermList ATmakeList(int n, ...);
Description: This function can be used to build an ATermList of n elements. The elements should be
passed as arguments 1 . . . n.
macro: ATmakeList0
Summary: Macro defined to point to the empty list []
Declaration: ATermList ATmakeList0()
function: ATmakeList1
Summary: Construct a list of one element
Declaration: ATermList ATmakeList1(ATerm el0);
function: ATmakeList2
Summary: Construct a list of two elements
Declaration: ATermList ATmakeList2(ATerm el0, el1);
function: ATmakeList3
Summary: Construct a list of three elements
Declaration: ATermList ATmakeList3(ATerm el0, el1, el2);
function: ATmakeList4
Summary: Construct a list of four elements
Declaration: ATermList ATmakeList4(ATerm el0, el1, el2, el3);
function: ATmakeList5
Summary: Construct a list of five elements
Declaration: ATermList ATmakeList5(ATerm el0, el1, el2, el3, el4);
16
function: ATmakeList6
Summary: Construct a list of six elements
Declaration: ATermList ATmakeList6(ATerm el0, el1, el2, el3, el4, el5);
Description: These functions build an ATermList of 1 . . . 6 elements. Longer lists should be created
using the generic ATmakeList function described above.
macro: ATgetLength
Summary: Macro to get the length of list l
Declaration: int ATgetLength(ATermList l)
macro: ATgetFirst
Summary: Macro to get the first element of list l
Declaration: ATerm ATgetFirst(ATermList l)
macro: ATgetNext
Summary: Macro to get the next part (the tail) of list l
Declaration: ATermList ATgetNext(ATermList l)
macro: ATisEmpty
Summary: Macro to test if list l is empty
Declaration: ATbool ATisEmpty(ATermList l)
function: ATgetTail
Summary: Return the sublist from start to the end of list.
Declaration: ATermList ATgetTail(ATermList list, int start);
function: ATreplaceTail
Summary: Replace the tail of list from position start with newtail
Declaration: ATermList ATreplaceTail(ATermList list, ATermList newtail, int
start);
function: ATgetPrefix
Summary: Return all but the last element of list
Declaration: ATermList ATgetPrefix(ATermList list);
function: ATgetLast
Summary: Return the last element of list
Declaration: ATerm ATgetLast(ATermList list);
function: ATgetSlice
Summary: Get a portion (slice) of a list
Declaration: ATermList ATgetSlice(ATermList list, int start, int end);
Description: Return the portion of list that lies between start and end. Thus start is included,
end is not.
function: ATinsert
Summary: Return list with el inserted.
Declaration: ATermlist ATinsert(ATermList list, ATerm el);
Description: The behaviour of ATinsert is of constant complexity. That is, the behaviour of ATinsert
does not degrade as the length of list increases.
function: ATinsertAt
Summary: Return list with el inserted at position index
17
Declaration: ATermList ATinsertAt((ATermList list, ATerm el, int index);
function: ATappend
Summary: Return list with el appended to it
Declaration: ATermList ATappend(ATermList list, ATerm el);
Description: Note that ATappend is implemented in terms of ATinsert by making a new list with
el as the first element and then ATinserting all elements from list. As such, the complexity of
ATappend is linear in the number of elements in list.
When ATappend is needed inside a loop that traverses a list (see parse list1 below), behaviour
of the loop will demonstrate quadratic complexity.
/* Example of parse_list that demonstrates quadratic complexity */
ATermList parse_list1(ATermList list)
{
ATerm
elem;
ATermList result = ATempty;
/* while list has elements */
while (!ATisEmpty(list))
{
/* Get head of list */
elem = ATgetFirst(list);
/* If elem satisfies some predicate (not shown here) then APPEND it to result */
if (some_predicate(elem) == ATtrue)
result = ATappend(result, elem);
/* Continue with tail of list */
list = ATgetNext(list);
}
/* Return the result list */
return result;
}
To avoid this behaviour, the inner loop could use ATinsert instead of ATappend to make the new
list. This will cause the resulting list to be in reverse order. A single ATreverse must therefore be
performed, but this can be done after the loop has terminated, bringing the behaviour down from quadratic
to linear complexity, but at the cost of two ATinserts per element (one for each ATinsert in the loop,
and an implicit one for each element through the use of ATreverse). An example is shown here in the
implementation of parse list2.
/* Example of parse_list that demonstrates linear complexity,
* using ATinsert instead of ATappend and reversing the list
* outside the loop just once. */
ATermList parse_list2(ATermList list)
{
ATerm
elem;
ATermList result = ATempty;
/* while list has elements */
while (!ATisEmpty(list))
{
/* Get head of list */
elem = ATgetFirst(list);
18
/* If elem satisfies some predicate (not shown here) then INSERT it to result */
if (some_predicate(elem) == ATtrue)
result = ATinsert(result, elem);
/* Continue with tail of list */
list = ATgetNext(list);
}
/* Return result after reversal */
return ATreverse(result);
}
An even further optimisation could make use of a locally allocated buffer. While traversing the list,
all elements that would normally be ATappended, are now placed in this buffer. Finally, the result is
obtained by starting with an empty list and ATinserting all elements from this buffer in reverse order.
As the cost of allocating and freeing a local buffer is by no means marginal, this solution should probably
only be applied when the loop appends more than just a few elements. The following example shows such
an implementation in parse list3.
/* Example of parse_list that demonstrates linear complexity,
* but which avoids using ATinsert twice, by inlining ATreverse
* using a local buffer. */
ATermList parse_list3(ATermList list)
{
int
pos = 0;
ATerm
elem;
ATerm
*buffer = NULL;
ATermList result = ATempty;
/* Allocate local buffer that can hold all elements of list */
buffer = (ATerm *) calloc(ATgetLength(list), sizeof(ATerm));
if (buffer == NULL) abort();
/* while list has elements */
while (!ATisEmpty(list))
{
/* Get head of list */
elem = ATgetFirst(list);
/* If elem satisfies some predicate (not shown here)
* then add it to buffer at next available position */
if (some_predicate(elem) == ATtrue)
buffer[pos++] = elem;
/* Continue with tail of list */
list = ATgetNext(list);
}
/* Now insert all elems in buffer to result */
for(--pos; pos >= 0; pos--)
result = ATinsert(result, buffer[pos]);
/* Release allocated resources */
free(buffer);
19
/* Return result */
return result;
}
function: ATconcat
Summary: Return the concatenation of list1 and list2
Declaration: ATermList ATconcat(ATermList list1, ATermList list2);
function: ATindexOf
Summary: Return the index of an ATerm in a list
Declaration: int ATindexOf(ATermList list, ATerm el, int start));
Description: Return the index where el can be found in list. Start looking at position start. Returns
-1 if el is not in list.
function: ATlastIndexOf
Summary: Return the index of an ATerm in a list (reverse)
Declaration: int ATlastIndexOf(ATermList list, ATerm el, int start));
Description: Search backwards for el in list. Start searching at start. Return the index of the first
occurrence of l encountered, or -1 when el is not present before start.
function: ATelementAt
Summary: Return a specific element of a list
Declaration: ATerm ATelementAt(ATermList list, int index));
Description: Return the element at position index in list. Return NULL when index is not in
list.
function: ATremoveElement
Summary: Return list with one occurrence of el removed
Declaration: ATermList ATremoveElement(ATermList list, ATerm el);
function: ATremoveAll
Summary: Return list with all occurrences of el removed
Declaration: ATermList ATremoveAll(ATermList list, ATerm el);
function: ATremoveElementAt
Summary: Return list with the element at index removed
Declaration: ATermList ATremoveElementAt(ATermList list, int index);
function: ATreplace
Summary: Return list with the element at index replaced by el
Declaration: ATermList ATreplace(ATermList list, ATerm el, int idx);
function: ATreverse
Summary: Return list with its elements in reversed order
Declaration: ATermList ATreverse(ATermList list));
function: ATfilter
Summary: Filter entries from a list using a predicate
Declaration: ATermList ATfilter(ATermList list, ATbool (*predicate)(ATerm));
Description: This function can be used to filter entries that satisfy a given predicate from a list. Each
item in list is judged through a call to predicate. If predicate returns ATtrue the entry is added
20
to a list, otherwise it is skipped. The function returns the list containing exactly those items that satisfy
predicate.
4.2.5 ATermPlaceholder
A placeholder is a special subtype used to indicate a typed hole in an ATerm. This can be used to create a
term of a specific type, even though its actual contents are not filled in.
function: ATmakePlaceholder
Summary: Build an ATermPlaceholder of a specific type. The type is taken from the type parameter.
See demo placeholder below.
Declaration: ATermPlaceholder ATmakePlaceholder(ATerm type);
macro: ATgetPlaceholder
Summary: Get the type of an ATermPlaceholder
Declaration: ATerm ATgetPlaceholder(ATermPlaceholder ph)
#include <assert.h>
#include <aterm2.h>
/* This example demonstrates the use of an ATermPlaceholder. It creates
* the function application "add" defined on two integers without actually
* using a specific integer: add(<int>,<int>).
*/
void demo_placeholder()
{
Symbol
sym_int, sym_add;
ATermAppl
app_add;
ATermPlaceholder ph_int;
/* Construct placeholder <int> using zero-arity function symbol "int" */
sym_int = ATmakeSymbol("int", 0, ATfalse);
ph_int = ATmakePlaceholder((ATerm)ATmakeAppl0(sym_int));
/* Construct add(<int>,<int>) using function symbol "add" with 2 args */
sym_add = ATmakeSymbol("add", 2, ATfalse);
app_add = ATmakeAppl2(sym_add, (ATerm)ph_int, (ATerm)ph_int);
/* Equal to constructing it using the level one interface */
assert(ATisEqual(app_add, ATparse("add(<int>,<int>)")));
/* Prints: Placeholder <int> is of type: int */
ATprintf("Placeholder %t is of type: %t\n", ph_int, ATgetPlaceholder(ph_int));
}
int main(int argc, char *argv[])
{
ATerm bottomOfStack;
ATinit(argc, argv, &bottomOfStack);
demo_placeholder();
return 0;
}
21
4.2.6 ATermBlob
function: ATmakeBlob
Summary: Build a Binary Large OBject given size (in bytes) and data
Declaration: ATermBlob ATmakeBlob(int size, void *data));
Description: This function can be used to create an ATerm of type blob, holding the data pointed to by
data. No copy of this data area is made, so the user should allocate this himself.
Note: due to the internal representation of a blob, size cannot exceed 2 24 in the current implementation.
This limits the size of the data area to 16 Mb.
macro: ATgetBlobData
Summary: Get the data section of blob
Declaration: void * ATgetBlobData(ATermBlob blob)
macro: ATgetBlobSize
Summary: Get the size (in bytes) of blob
Declaration: int ATgetBlobSize(ATermBlob blob)
function: ATregisterBlobDestructor
Summary: Register a blob-destructor function
Declaration: void ATregisterBlobDestructor(ATbool (*destructor)(ATermBlob));
Description: When a blob-destructor function has been registered, it will be called whenever the garbage
collector deletes an ATermBlob. The destructor function can then handle the deletion of the data area of
the blob. At most 16 blob destructor functions can be registered in the current implementation.
function: ATunregisterBlobDestructor
Summary: Unregister a previously registered blob-destructor function
Declaration: void ATunregisterBlobDestructor(ATbool (*destructor)(ATermBlob));
Description: This removes a blob-destructor that has been previously installed through a call to ATregisterBlobDestructor
4.3 Dictionaries
Dictionaries are datastructures which allow looking up a certain ATerm given another ATerm. The dictionary itself is also an ATerm and as such is subject to the ATerm Library rules of garbage collection. Each
dictionary consists of its own list of ATerms. For each lookup in the dictionary, the list is traversed to
see if the current element’s key matches the one being looked up. A lookup in a dictionary demonstrates
behaviour linear in the number of elements the dictionary contains. On average fifty percent of the number
of elements in the dictionary are examined before a match is found (if the element is present at all). For a
more efficient ATerm-to-ATerm mapping, see Tables in section 4.4.
function: ATdictCreate
Summary: Create a new dictionary
Declaration: ATerm ATdictCreate();
function: ATdictGet
Summary: Get the value belonging to a given key in a dictionary.
Declaration: ATerm ATdictGet(ATerm dict, ATerm key);
function: ATdictPut
22
Summary: Add / update a (key, value)-pair in a dictionary
Declaration: ATerm ATdictPut(ATerm dict, ATerm key, ATerm value);
Description: If key does not already exist in the dictionary, this function adds the (key, value)-pair to
the dictionary. Otherwise, it updates the value to value. The modified dictionary is returned.
function: ATdictRemove
Summary: Remove the (key, value)-pair from the dictionary
Declaration: ATerm ATdictRemove(ATerm dict, ATerm key);
Description: This function can be used to remove an entry from the dictionary. If the entry was actually
in the dictionary, the modified dictionary is returned. If the entry was not in the dictionary in the first place,
the (unmodified) dictionary itself is returned.
4.4 Tables
The dictionaries described in Section 4.3 are in essence nothing more than linked lists, which makes them
less suitable for large ATerm-to-ATerm mappings. To this end, ATerm tables were created. These are
efficiently implemented using a hash table requiring approximately 16 bytes per stored entry, assuming
that the hash table is filled for 50%.
function: ATtableCreate
Summary: Create an ATermTable
Declaration: ATermTable ATtableCreate(int initial size, int max load pct);
Description: This function creates an ATermTable given an initial size and a maximum load percentage.
Whenever this percentage is exceeded (which is detected when a new entry is added using ATtablePut),
the table is automatically expanded and all existing entries are rehashed into the new table. If you know
in advance approximately how many items will be in the table, you may set it up in such a way that no
resizing (and thus no rehashing) is necessary. For example, if you expect about 1000 items in the table, you
can create it with its initial size set to 1333 and a maximum load percentage of 75%. You are not required
to do this, it merely saves a runtime expansion and rehashing of the table which increases efficiency.
function: ATtableDestroy
Summary: Destroy an ATermTable
Declaration: void ATtableDestroy(ATermTable table);
Description: Contrary to ATermDictionaries, ATermTables are themselves not ATerms. This means they
are not freed by the garbage collector when they are no longer referred to. Therefore, when the table is no
longer needed, the user should release the resources allocated by the table by calling ATtableDestroy.
All references the table has to ATerms will then also be removed, so that those may be freed by the garbage
collector (if no other references to them exist of course).
function: ATtableReset
Summary: Reset an ATermTable
Declaration: void ATtableReset(ATermTable table);
Description: This function resets an ATermtable, without freeing the memory it occupies. Its effect is the
same as the subsequent execution of a destroy and a create of a table, but as no memory is released and
obtained from the C memeory management system this function is generally cheaper. but if subsequent
tables differ very much in size, the use of ATtableDestroy and ATtableCreate may be prefered,
because in such a way the sizes of the table adapt automatically to the requirements of the application.
function: ATtablePut
Summary: Add / update a (key, value)-pair in a table
Declaration: void ATtablePut(ATermTable table, ATerm key, ATerm value);
Description: If key does not already exist in the table, this function adds the (key, value)-pair to the
table. Otherwise, it updates the value to value.
23
function: ATtableGet
Summary: Get the value belonging to a given key in a table
Declaration: ATerm ATtableGet(ATermTable table, ATerm key);
function: ATtableRemove
Summary: Remove the (key, value)-pair from table
Declaration: void ATtableRemove(ATermTable table, ATerm key);
function: ATtableKeys
Summary: Get an ATermList of all the keys in a table
Declaration: ATermList ATtableKeys(ATermTable table);
Description: This function can be useful if you need to iterate over all elements in a table. It returns an
ATermList containing all the keys in the table. The corresponding values of each key you are interested in
can then be retrieved through respective calls to ATtableGet.
4.5 Indexed sets
The data type ATermIndexedSet provides a mapping or table from ATerms to numbers, where it
attempts to assign the numbers from one upwards subsequently to each entered term. If a number is
assigned to a term, the term will remain assigned until the term is removed from the table. When assigning
numbers to newly entered elements, numbers previously assigned to elements that have been removed are
used first.
This datatype can be used for different purposes. In the first place one can make a mapping from
ATerms to elements in any arbitrary domain D with it. By entering the ATerms in an ATermIndexedSet
each ATerm gets a subsequent number. These numbers can be used as entries in a table to obtain the element of sort D belonging to the ATerm.
Another type of application is the use as a set. Suppose that a sequence of ATerms must be dealt
with. Suppose that the sequence can contain identical ATerms, and that each unique ATerm needs to be
treated only once. Then each treated ATerm can be entered in the indexed set. For each to be investigated
ATerm one inspection of the indexed set suffices to know whether this ATerm has already been considered.
A particular instance of this kind of application is the exploration of state spaces, where each state is
represented by an ATerm.
The implementation ATermIndexedSets and ATermTables are strongly connected. The implementation is quite efficient both in time and space, only requiring 12 bytes for each entry in an indexed set,
if the hash table, which forms it core, is half full.
function: ATindexedSetCreate
Summary: Create a new ATermIndexedSet
Declaration: ATermIndexedSet ATindexedSetCreate(long initial size, int max load pct);
Description: This function creates an ATermIndexedSet with approximately the size initial size,
where it guarantees that the internal hash table, will be filled up to max load pct percent. If needed,
the size of the hash table is dynamically extended to hold the entries inserted into it. If extension of the
hash table fails due to lack of memory. it is attempted to fill the hash table up to 100%. All elements
entered into the indexed set are automatically protected. Note that for each ATindexedSetCreate
an ATindexedSetDestroy must be carried out to free memory, and to allow inserted elements to be
released by the automatic garbage system of the ATerm library. Carrying out a ATindexedSetReset
does not free the memory, but allows inserted elements to be garbage collected.
function: ATindexedSetDestroy
Summary: This function releases all memory occupied by the ATermIndexedSet.
Declaration: void ATindexedSetDestroy(ATermIndexedSet set);
24
function: ATindexedSetReset
Summary: Clear the hash table in the set.
Declaration: void ATindexedSetReset(ATermIndexedSet set);
Description: This function clears the hash table in the set, but does not release the memory. Using
ATindexedSetReset instead of ATindexedSetDestroy is preferable when indexed sets of approximately the same size are being used.
function: ATindexedSetPut
Summary: Enter elem into the set.
Declaration: long ATindexedSetPut(ATermIndexedSet set, ATerm elem, ATbool *new);
Description: This functions enters elem into the set. If elem was already in the set the previously
assigned index of elem is returned, and new is set to false. If elem did not yet occur in set a new
number is assigned, and new is set to true. This number can either be the number of an element that has
been removed, or, if such a number is not available, the lowest non used number is assigned to elem and
returned. The lowest number that is used is 0.
function: ATindexedSetGetIndex
Summary: Find the index of elem in set
Declaration: long ATindexedSetGetIndex(ATermIndexedSet set, ATerm elem);
Description: The index assigned to elem is returned, except when elem is not in the set, in which case
the return value is a negative number.
function: ATindexedSetGetElem
Summary: Retrieve the element at index in set
Declaration: ATerm ATindexedSetGetElem(ATermIndexedSet set, long index);
Description: This function must be invoked with a valid index and it returns the elem assigned to this
index. If it is invoked with an invalid index, effects are not predictable.
function: ATindexedSetRemove
Summary: Remove elem from set
Declaration: void ATindexedSetRemove(ATermIndexedSet set, ATerm elem);
Description: The elem is removed from the indexed set, and if a number was assigned to elem, it is
freed to be reassigned to an element, that may be put into the set at some later instance.
function: ATindexedSetElements
Summary: Retrieve all elements in set
Declaration: ATermList ATindexedSetElements(ATermIndexedSet set);
Description: A list with all valid elements stored in the indexed set is returned. The list is ordered from
element with index 0 onwards.
5 Utilities
This section describes the utilities that come with the ATerm Library. These utilities are automatically built
when the ATerm Library is compiled and installed.
5.1 ATerm-conversion: baffle
This utility can be used to convert between the different ATerm formats: text, baf, and taf.
Usage: baffle [-i <input>] [-o <output> | -c] [-v] [-rb | -rt | -rs] [-wb | -wt | -rs]
-i <input>
- Read input from file <input>
25
(Default: stdin)
-o <output>
-c
-v
-h
-rb, -rt, -rs
-wb, -wt
-
Write output to file <output>
(Default: stdout)
Check validity of input-term
Print version information
Display help
Choose between BAF, TEXT, and TAF input (Default: autodetect)
Choose between BAF, TEXT and TAF output (Default: -wb)
Some small scripts are included which can be used to connect a process producing one ATerm format
to a process which expects another. These scripts just set up baffle with the appropriate switches and
redirect stdin and stdout accordingly. These scripts are appropriately called: trm2baf, baf2trm,
trm2taf, taf2trm, baf2taf, and taf2baf.
5.2 Calculating an ATerm’s size: termsize
This utility can be used to calculate three things:
• core size: the amount of memory a given ATerm needs;
• text size: the amount of memory needed to hold a textual representation of an ATerm;
• tree depth: the maximum depth of a term.
The results are written to stdout. As termsize uses ATreadFromFile, it can calculate the size of
both textual and BAF representations of ATerms.
Usage: termsize < inputfile.
5.3 Calculating MD5 checksum of an ATerm: atsum
This utility can be used to print the MD5 checksum of the TAF representation of an ATerm. The algorithm
used is the RSA Data Security, Inc. MD5 Message-Digest Algorithm (see RFC1321).
Usage: atsum [inputfile].
5.4 Calculating differences between two ATerms: atdiff
This utility compares two terms and prints a template term that covers the common parts containing
<diff> placeholders for subterms that differed, and a list of their differing subterms.
Usage: atdiff [<options>] <file1> <file2>
Options:
--nodiffs | --diffs <diff-file>
--notemplate | --template <template-file>
26
(default: stdout)
(default: stdout)
Index
ATinsert, 17
ATinsertAt, 17
ATisEmpty, 17
ATisEqual, 10
ATisQuoted, 15
ATlastIndexOf, 20
ATmake, 7
ATmakeAFun, 14
ATmakeAppl, 15
ATmakeAppl0, 15
ATmakeAppl1, 15
ATmakeAppl2, 15
ATmakeAppl3, 15
ATmakeAppl4, 15
ATmakeAppl5, 15
ATmakeAppl6, 15
ATmakeApplArray, 16
ATmakeApplList, 16
ATmakeBlob, 22
ATmakeInt, 13
ATmakeList, 16
ATmakeList0, 16
ATmakeList1, 16
ATmakeList2, 16
ATmakeList3, 16
ATmakeList4, 16
ATmakeList5, 16
ATmakeList6, 17
ATmakePlaceholder, 21
ATmakeReal, 14
ATmakeTerm, 8
ATmatch, 8
ATparse, 10
ATprintf, 11
ATprotect, 12
ATprotectAFun, 14
ATprotectArray, 13
ATreadFromBinaryFile, 9
ATreadFromBinaryString, 9
ATreadFromFile, 9
ATreadFromNamedFile, 9
ATreadFromSharedString, 9
ATreadFromSharedTextFile, 9
ATreadFromString, 9
ATreadFromTextFile, 9
ATregisterBlobDestructor, 22
ATremoveAll, 20
ATremoveAnnotation, 11
ATremoveElement, 20
ATremoveElementAt, 20
ATreplace, 20
ATabort, 12
ATappend, 18
ATBconnect, 32
ATBdisconnect, 32
ATBeventloop, 32
ATBgetDescriptors, 33
ATBhandleAny, 33
ATBhandleOne, 33
ATBinit, 32
ATBpeekAny, 33
ATBpeekOne, 33
ATBreadTerm, 33
ATBwriteTerm, 33
ATconcat, 20
ATdictCreate, 22
ATdictGet, 22
ATdictPut, 22
ATdictRemove, 23
ATelementAt, 20
ATerror, 12
ATfilter, 20
ATfprintf, 11
ATgetAFun, 15
ATgetAnnotation, 11
ATgetArgument, 15
ATgetArguments, 16
ATgetArity, 15
ATgetBlobData, 22
ATgetBlobSize, 22
ATgetFirst, 17
ATgetInt, 14
ATgetLast, 17
ATgetLength, 17
ATgetName, 14
ATgetNext, 17
ATgetPlaceholder, 21
ATgetPrefix, 17
ATgetReal, 14
ATgetSlice, 17
ATgetTail, 17
ATgetType, 10
ATindexedSetCreate, 24
ATindexedSetDestroy, 24
ATindexedSetElements, 25
ATindexedSetGetElem, 25
ATindexedSetGetIndex, 25
ATindexedSetPut, 25
ATindexedSetRemove, 25
ATindexedSetReset, 25
ATindexOf, 20
ATinit, 11
27
ATreplaceTail, 17
ATreverse, 20
ATsetAbortHandler, 12
ATsetAnnotation, 11
ATsetArgument, 16
ATsetErrorHandler, 12
ATsetWarningHandler, 12
ATtableCreate, 23
ATtableDestroy, 23
ATtableGet, 24
ATtableKeys, 24
ATtablePut, 23
ATtableRemove, 24
ATtableReset, 23
ATunprotect, 13
ATunprotectAFun, 14
ATunprotectArray, 13
ATunregisterBlobDestructor, 22
ATvfprintf, 11
ATvmake, 8
ATvmakeTerm, 8
ATwarning, 12
ATwriteToBinaryFile, 10
ATwriteToBinaryString, 11
ATWriteToNamedBinaryFile, 10
ATWriteToNamedTextFile, 10
ATwriteToSharedString, 11
ATwriteToSharedTextFile, 10
ATwriteToString, 10
ATwriteToTextFile, 10
28
References
[BJKO00]
M.G.J. van den Brand, H.A. de Jong, P. Klint, and P.A. Olivier. Efficient Annotated Terms.
Software – Practice & Experience, 30:259–291, 2000.
[BKMO97] M.G.J. van den Brand, T. Kuipers, L. Moonen, and P. Olivier. Design and implementation of a
new asf+sdf meta-environment. In A. Sellink, editor, Proceedings of the Second International
Workshop on the Theory and Practice of Algebraic Specifications (ASF+SDF’97), Workshops
in Computing, Amsterdam, November 1997. Springer-Verlag.
[BOHK98] M.G.J. van den Brand, P. Olivier, J. Heering, and P. Klint. Compiling Rewrite Systems: The
ASF+SDF Compiler. Technical report, CWI/University of Amsterdam, 1998. In preparation.
A
The ToolBus layer
The ATerm library also provides functionality needed to implement ToolBus tools. This section describes
this ToolBus layer in detail.
A.1 Generation of tool interfaces
The ATerm library provides a program that takes a standard ToolBus tifs file, which is generated by the
toolbus interpreter when started with the -gentifs option, and generates a tool interface in C for use
with the ATerm library.
The generated interface consists of two files, a C source file and a C header (include) file. In the header
file a number of interface functions is declared, one for each element in the input signature of the tool. It is
up to the writer of the tool to provide an implementation for these functions. The generated C file contains
a handler function that analyzes incoming terms from the ToolBus, and delegates to the appropriate
interface function.
A.2 Example
Suppose we take the following simple ToolBus script "test.tb":
tool testing is { command = "./testing" }
process TEST is
let
T : testing,
R : str
in
execute(testing, T?) .
snd-do(T, f1(42)) .
snd-eval(T, f2("hello world!")) .
rec-value(T, result(R?)) .
printf("result: %s\n", R)
endlet
toolbus(TEST)
Using the command:
toolbus -gentifs test.tb
we generate a file called "test.tifs". Using the command:
tifstoc -tool testing test.tifs
29
we generate the header file "testing.tif.h" and the source file "testing.tif.c".
"testing.tif.h" looks like this:
/**
* This file is generated by tifstoc. Do not edit!
* Generated from tifs for tool ’testing’
* Headerfile generated at Thu Apr 22 11:37:36 1999
*/
#ifndef _TESTING_H
#define _TESTING_H
#include <atb-tool.h>
/* Prototypes for functions called from the event handler */
void f1(int conn, int);
ATerm f2(int conn, char *);
void rec_terminate(int conn, ATerm);
extern ATerm testing_handler(int conn, ATerm term);
extern ATerm testing_checker(int conn, ATerm sigs);
#endif
Only the functions f1, f2, and rec terminate together with a simple main function have to be implemented to build a fully functional ToolBus tool. The implementation of the functions testing handler
and testing checker has been generated in the file "testing.tif.c", which looks like this:
/**
* This file is generated by tifstoc. Do not edit!
* Generated from tifs for tool ’testing’
* Implementation generated at Thu Apr 22 11:37:36 1999
*/
#include "testing.tif.h"
#define NR_SIG_ENTRIES
3
static char *signature[NR_SIG_ENTRIES] = {
"rec-terminate(<testing>,<term>)",
"rec-eval(<testing>,f2(<str>))",
"rec-do(<testing>,f1(<int>))",
};
/* Event handler for tool ’testing’ */
ATerm testing_handler(int conn, ATerm term)
{
ATerm in, out;
/* We need some temporary variables during matching */
int i0;
char *s0;
ATerm t0;
if(ATmatch(term, "rec-eval(f2(<str>))", &s0)) {
return f2(conn, s0);
}
30
if(ATmatch(term, "rec-terminate(<term>)", &t0)) {
rec_terminate(conn, t0);
return NULL;
}
if(ATmatch(term, "rec-do(f1(<int>))", &i0)) {
f1(conn, i0);
return NULL;
}
if(ATmatch(term, "rec-do(signature(<term>,<term>))", &in, &out)) {
ATerm result = testing_checker(conn, in);
if(!ATmatch(result, "[]"))
ATfprintf(stderr, "warning: not in input signature:\n\t%\n\tl\n", result);
return NULL;
}
ATerror("tool testing cannot handle term %t", term);
return NULL; /* Silence the compiler */
}
/* Check the signature of the tool ’testing’ */
ATerm testing_checker(int conn, ATerm siglist)
{
return ATBcheckSignature(siglist, signature, NR_SIG_ENTRIES);
}
This file contains an array of signature definitions (signature), the handler function (testing handler),
and the signature checker (testing checker). The only thing the handler does is differentiating between the different possible input terms coming from the ToolBus, and delegating the actual work to the
appropriate function.
As mentioned earlier, the only thing needed to implement the actual tool, is the implementation of the
three interface functions f1, f2, and rec terminate, and the implementation of main to get things
going. We will first take a look at the initialization stuff that the main function has to do:
#include "testing.tif.h"
int main(int argc, char *argv[])
{
ATerm bottomOfStack;
ATBinit(argc, argv, &bottomOfStack);
if(ATBconnect(NULL, NULL, -1, testing_handler) >= 0) {
ATBeventloop();
} else {
fprintf(stderr, "Could not connect to the ToolBus, giving up!\n");
return -1;
}
return 0;
}
The variable bottomOfStack is needed by the ATerm library to determine where to look for the
stack. argc and argv are passed unchanged to ATBinit, so the ToolBus library can look for default
values for things like the ToolBus socket address and the ToolBus host name.
The call to ATBconnect connects to a running ToolBus, and requires four arguments: a character
string representing the tool name, a character string representing the host name of the ToolBus to connect
31
to, the port number of the ToolBus to connect to, and a handler function. Passing NULL, NULL, and -1
respectively as the tool name, the host name, and the port number cause the defaults for these values to be
used instead.
When all goes well, the call to ATBeventloop starts the main ToolBus eventloop and the tool will
be ready to receive requests from the ToolBus.
Now we only need the implementation of the three interface functions:
void f1(int conn, int value)
{
printf("f1 called: %d\n", value);
}
ATerm f2(int conn, char *value)
{
return ATmake("snd-value(result(<str>))", value);
}
void rec_terminate(int conn, ATerm arg)
{
exit(0);
}
Note that the conn argument identifies the ToolBus connection, making it possible to distinguish
which ToolBus made the request when connected to more than one ToolBus at the same time.
A.3 Functions in the ToolBus layer
The ToolBus layer offers the following functions:
function: ATBinit
Summary: Initialize the ToolBus layer and the underlying ATerm library when needed.
Declaration: int ATBinit(int argc, char *argv[], ATerm *stack bottom);
Description: The return value indicates whether or not the ToolBus host could be found. 0 indicates that
all is well, and -1 indicates an error, in which case errno is set to indicate which error.
function: ATBconnect
Summary: Connect to a running ToolBus.
Declaration: int ATBconnect(char *toolname, char *host, int port, ATBhandler
h);
Description: When NULL is passed as toolname or host, or -1 is passed as port, default values are
taken from argv passed to ATBinit. The return value indicates whether or not the connection succeeded.
-1 means that the connection failed and a positive number or zero indicates a succesful connection attempt.
In this case this number is also the file descriptor of the socket connection to the ToolBus.
function: ATBdisconnect
Summary: Disconnect a from a ToolBus.
Declaration: void ATBdisconnect(int fd);
Description: This function can be used to terminate a connection that has been established earlier using
ATBconnect
function: ATBeventloop
Summary: Start the tool event loop, reading and handling terms until a connection is broken.
Declaration: int ATBeventloop(void);
Description: This function will not return unless something goes wrong!
32
function: ATBwriteTerm
Summary: Send a term to the ToolBus.
Declaration: int ATBwriteTerm(int fd, ATerm term);
Description: A term is send using the ToolBus connection indicated by fd. This function is typically
used to generate ToolBus events, for instance:
ATBwriteTerm(fd, ATparse("snd-event(some-event)")); When something goes wrong,
-1 is returned, otherwise 0 is returned.
A.4 Control flow without the ATBeventloop
In some situations, the ATBeventloop function does not offer the right flow of control for a specific
application. In this case, the following set of functions can be used to create custom control flow patterns:
function: ATBpeekOne
Summary: Check if there is input waiting on a ToolBus connection
Declaration: ATbool ATBpeekOne(int fd);
Description: If there is input waiting on the specified connection, ATtrue is returned. Otherwise,
ATfalse is returned.
function: ATBpeekAny
Summary: Check if there is input waiting on any ToolBus connection
Declaration: int ATBpeekAny();
Description: If there is input waiting on one of the ToolBus connections, the appropriate file-descriptor
is returned. Otherwise, -1 is returned. This function provides for some ‘fairness’ by using a round-robin
scheme in traversing the connections between calls.
function: ATBreadTerm
Summary: Read a term from a ToolBus connection.
Declaration: ATerm ATBreadTerm(int fd);
function: ATBhandleOne
Summary: Read one term from a ToolBus connection, and call the appropriate handler. -1 is returned
when something goes wrong.
Declaration: int ATBhandleOne(int fd);
function: ATBhandleAny
Summary: Read a single term from any ToolBus connection and call the appropriate handler. -1 is
returned when something goes wrong.
Declaration: int ATBhandleAny();
function: ATBgetDescriptors
Summary: Gather all ToolBus connection file descriptor in a single descriptor set. The return value
indicates the maximum value of any descriptor in the set.
Declaration: int ATBgetDescriptors(fd set *set);
Note that the standard ATBeventloop can be expressed using the following code:
int ATBeventloop(void)
{
int fd;
while(ATtrue) {
fd = ATBhandleAny();
if(fd < 0)
return -1;
}
33
}
B Java implementation
Besides the C implementaton discussed upto now, we also developed a Java implementation of the ATerm
datatype. We have tried to keep the interfaces of the C implementation and the Java implementation as
close together as possible. Unfortunately, constraints imposed by both languages prohibit the use of a
single interface for both languages. In this section we will discuss the Java interface, and highlight the
differences with the C interface where appropriate.
Most differences are introduced by the fact that Java is a much more powerful language than C. Garbage
collection for instance is a built-in feature of the Java language, so no protect and unprotect functions are needed in Java.
B.1
Interfaces and Implementation
The interface ATerm defines functionality relevant for all ATerm subtypes. Each of these ATerm subtypes
has its own interface, describing the additional functionality relevant for that particular subtype.
An interface ATermFactory describes the various methods used to create new ATerm objects. It is
used to implement maximal sharing.
A complete description of these interfaces can be found in the file java-api.ps which is distributed
with this manual.
The ATerm library distribution so far comes with a single implementation of the ATerm interfaces. This
implementation is a “pure” Java one, but plans exist to experiment with an implementation using the Java
Native Interface (JNI) to build a layer of Java code on top of the C implementation.
A very basic example that shows the creation of some ATerms and how to read one from a stream is
shown below.
import java.io.*;
import aterm.*;
public class Basic
{
private ATermFactory factory;
public static final void main(String[] args) throws IOException {
Basic basic = new Basic(args);
}
public Basic(String[] args) throws IOException {
factory = new aterm.pure.PureFactory();
ATermInt i = factory.makeInt(42);
System.out.println("i = " + i);
AFun fun = factory.makeAFun("foo", 2, false);
ATermAppl foo = factory.makeAppl(fun, i, i);
System.out.println("foo = " + foo);
ATerm t = factory.parse("this(is(a(term(0))))");
System.out.println("t = " + t);
try {
ATerm input = factory.readFromFile(System.in);
34
System.out.println("You typed a valid term: " + input);
} catch (ParseError error) {
System.out.println("Your input was not a valid term!");
}
}
}
B.2
Class hierarchy
Because Java is an object oriented language, we have partitioned the Java implementation in a number of
classes. The resulting class hierarchy is shown in Figure 1.
Is−a relation
Factory
Part−of relation
1
n
ATerm
ATermPlaceholder
ATermInt
ATermReal
1 type
1
ATermAppl
ATermList
1 args
1
1
1
next
1 first
1
Figure 1: Simple ATerm class library
C
Connecting Java tools
This section shows how to write a simple Java application and which steps need to be taken to connect it
to the ToolBus.
The example tool is a simple Java Application which pops up a GUI with a button that can be pressed
by the user. Further, it contains a method msg which can be called by the ToolBus. This method prints the
string that was passed and returns a count indicating the message number.
In order to get from the ToolBus script example.tb to the generated .java files, we follow steps
similar to the procedure to connect a C program to the ToolBus.
• Generate Tool Interface file example.tifs
˜/tmp > toolbus -gentifs example.tb
Tool interfaces written to ‘example.tifs’
• Generate Java code for tool example
˜/tmp > tifstojava -tool example -tifs example.tifs
generating file ExampleTif.java
generating file ExampleTool.java
generating file ExampleBridge.java
As you can see, three files are generated for our Example tool:
• ExampleTif.java the Java interface describing our Tool’s functionality.
35
• ExampleTool.java an abstract implementation of ExampleTif.java containing just enough
code to check the input/output signature of our tool and handle incoming messages by dispatching
them to the correct method.
• ExampleBridge.java a concrete class extending ExampleTool.java which can be used as
a bridge between your Tool class and the ToolBus.
Remember that Java only allows extention of a single class, but does allow your class to implement
multiple interfaces. Using the generated Bridge allows your class to extend another class, but still save
you the arduous task of extending the generic AbstractTool class for each new tool. Have a look at the
source code of example.tb and Example.java below.
example.tb looks like this:
tool example is { command="java-adapter -class Example" }
process EXAMPLE is
let
T : example,
Value : int,
Name : str
in
execute(example, T?) .
(
snd-eval(T, msg("Hello World!")) delay(sec(3)) .
rec-value(T, count(Value?)) .
printf("Hello number %d\n", Value)
) * delta
||
(
rec-event(T, button(Name?)) .
printf("Button pressed: %s\n", Name) .
snd-ack-event(T, button(Name))
) * delta
endlet
toolbus(EXAMPLE)
Example.java looks like this:
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import aterm.*;
public class Example
extends Frame
implements ExampleTif, ActionListener
{
private ATermFactory factory;
private ExampleBridge bridge;
private Button button;
private int count;
36
public static final void main(String[] args)
throws IOException
{
Example example = new Example(args);
}
public Example(String[] args)
throws IOException
{
factory = new aterm.pure.PureFactory();
// Build the user interface: just a single button
button = new Button("Button");
button.addActionListener(this);
add(button);
pack();
show();
// Create the bridge that will forward incoming messages
// to method calls in this Example object
bridge = new ExampleBridge(factory, this);
// Initialize vital parameters, like the ToolBus TCP/IP port, tool name,
// etc. that are passed to us using the command line arguments.
bridge.init(args);
// Actually establish the connection with the ToolBus
bridge.connect();
// Start the tool event loop
bridge.run();
}
public void actionPerformed(ActionEvent event)
{
if (event.getSource() == button) {
// When the user presses the button, we send an event to the ToolBus
bridge.postEvent(factory.make("button(<str>)", button.getLabel()));
}
}
public ATerm msg(String message)
{
// Print the incoming message
System.out.println("Example tool received msg: " + message);
// Increase the counter and return the current value to the ToolBus
return factory.make("snd-value(count(<int>))", new Integer(count++));
}
public void recAckEvent(ATerm event)
{
// This simple tool ignores event acknowledgements
37
}
public void recTerminate(ATerm arg)
{
// Just exit when the ToolBus terminates
System.exit(0);
}
}
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