18.3 Invocation (4tH script). 4tH 4tH Forth compiler

PDF

Dokument

Oglas

CHAPTER 18. PREPROCESSOR MANUAL hello’s 10

364

It is even powerful enough to resolve a CASE..ENDCASE construct:

:macro case >>> 0 ;

:macro of over = if drop ;

:macro endof else >>> 1 @add ;

:macro endif @if then >>> -1 @add endif ;

:macro endcase drop endif @drop ;

: .WEEKDAY ( daynum --- )

CASE

1 OF ." Sunday"

2 OF ." Monday"

ENDOF

3 OF ." Tuesday" ENDOF

4 OF ." Wednesday" ENDOF

5 OF ." Thursday" ENDOF

6 OF ." Friday" ENDOF

7 OF ." Saturday" ENDOF

ENDCASE ;

With @minus you can negate a number on the stack, so subtractions are possible too.

Multiplications can also be performed by using @mul. Divisions are supported by the

@divrm function, which leaves the division and modulo on the stack. If you want to evaluate the result of an arithmetic expression, you can use @sign. @sign returns -1 when the top of the string stack is negative, 1 when it is positive and else zero. It closely resembles the [SIGN] directive of 4tH.

@cell will leave a true flag on the stack if the top of the stack can be converted to a number. Some stack instructions are provided as well, like @drop, @dup, @nip and

@over . They work exactly like their 4tH counterparts. @cr simply issues a newline.

The most elusive function may be @eval. If the top of the string stack contains the name of a user-defined macro, it will be executed. If it doesn’t, the top of the stack is simply printed. You can use this function to interpret a string of user-defined macro’s or simply print the top of the stack.

You can check the existence of a user-defined macro with @exist, which leaves a nonzero value if the top of the string stack is the name of a user-defined macro. Finally,

@match will compare the two topmost items on the string stack and leave a zero value if they match.