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Archive-name: ForthFaq/CASE_ENDCASE
Last-modified: 30.Jan.93
Version: 1.1
[This is a message that I thought deserved to be preserved. -dwp]
From: eaker@ukulele.crd.ge.com (Chuck Eaker)
Subject: Re: Wanted .. CASE,OF,ENDOF,ENDCASE
Message-ID: <1992Nov25.164255.23225@crd.ge.com>
Date: 25 Nov 92 16:42:55 GMT
In article <jax.722669998@well.sf.ca.us>,
jax@well.sf.ca.us (Jack J. Woehr) writes:
|> In <1992Nov24.101857.84@wronz.org.nz> mentink@wronz.org.nz writes:
|>
|>
|>
|> > Can anyone help with source ( masm/forth) to the CASE statement
|> > word set. I.E .... CASE OF ENDOF ENDCASE ....
|>
|> Baden's CASE is in FORTH Dimensions VIII/5.
|>
|> Eaker, who wrote and enduring CASE construct, checks into
|> this newsgroup once and a while. Charles?
|>
|> =jax=
|> --
|> # jax@well.{UUCP,sf.ca.us} # # Member # # Vice President, #
|> # du!isis!koscej!jax # # X3J14 TC # # Forth Interest Group #
|> # JAX on GEnie # # for ANS # # P.O. Box 8231 #
|> # SYSOP RCFB (303) 278-0364 # # Forth # # San Jose CA 95155 #
1. FIG-Forth
Here is the source for FIG-Forth published with the original article
(Forth Dimensions, Vol. II, No. 3, pp. 37-40.). The ?PAIRS word was
FIG-Forth's way of implementing a small amount of syntax checking.
: CASE ?COMP CSP @ !CSP 4 ; IMMEDIATE
: OF 4 ?PAIRS COMPILE OVER COMPILE = COMPILE OBRANCH
HERE 0 , COMPILE DROP 5 ; IMMEDIATE
: ENDOF 5 ?PAIRS COMPILE BRANCH HERE 0 ,
SWAP 2 [COMPILE] ENDIF 4 ; IMMEDIATE
: ENDCASE 4 ?PAIRS COMPILE DROP
BEGIN SP@ CSP @ = 0=
WHILE 2 [COMPILE ENDIF REPEAT
CSP ! ; IMMEDIATE
1a. Here is additional source for FIG-Forth published in Forth
Dimensions, Vol. III, No. 6, pp. 187-188 in an article by Alfred J.
Monroe. He adds a primitive compiled by OF which reduces the amount
of code compiled by OF. Use the definitions of CASE, ENDOF, and
ENDCASE given above.
: (OF) OVER = IF DROP 1 ELSE 0 ENDIF ;
: OF 4 ?PAIRS COMPILE (OF) COMPILE 0BRANCH
HERE 0 , 5 ; IMMEDIATE
Mr. Monroe also gave code for some interesting variants:
: (<OF) OVER > IF DROP 1 ELSE 0 ENDIF ;
: <OF 4 ?PAIRS COMPILE (<OF) COMPILE 0BRANCH
HERE 0 , 5 ; IMMEDIATE
: (>OF) OVER > IF DROP 1 ELSE 0 ENDIF ;
: >OF 4 ?PAIRS COMPILE (>OF) COMPILE 0BRANCH
HERE 0 , 5 ; IMMEDIATE
: RANGE >R OVER DUP R> 1+ < IF SWAP 1- > IF DROP 1 ELSE 0
ENDIF ELSE DROP DROP 0 ENDIF ;
: RNG-OF 4 ?PAIRS COMPILE RANGE COMPILE 0BRANCH
HERE 0 , 5 ; IMMEDIATE
1b. It is quite common to define (OF) as a CODE word and have
it combine the functions of the run-time (OF) and the compile-time
0BRANCH in the previous definitions. This reduces the amount of
compiled code even more.
CODE (OF) ( 1. Remove the top element of the stack and call it A.
2. If A equals the new top element of the stack,
remove the new top element of the stack,
skip over the branch vector, and execute
the code which follows it.
Else
continue execution at the location indicated
by the branch vector.
) END-CODE
: OF 4 ?PAIRS COMPILE (OF) HERE 0 , 5 ; IMMEDIATE
2. dpANS-3
dpANS-3 contains the following definitions (p. 133) to illustrate
control structure extension. Note that it would be quite easy to
optimize OF along the lines suggested above. Note also that there is no
syntax checking. These words may appear anywhere and not necessarily
combined with each other. In fact, ENDOF may be dispensed with entirely
and replaced with ELSE. Compile-time monitoring of the syntax of
control structure words is a perennial Forth problem.
0 CONSTANT CASE IMMEDIATE ( init count of OFs )
: OF ( #of -- orig #of+1 / x -- )
1+ ( count OFs )
>R ( move off the stack in case the control-flow )
( stack is the data stack. )
POSTPONE OVER POSTPONE = ( copy and test case value )
POSTPONE IF ( add orig to control flow stack )
POSTPONE DROP ( discards case value if = )
R> ; ( we can bring count back now )
IMMEDIATE
: ENDOF ( orig1 #of -- orig2 #of )
>R ( move off the stack in case the control-flow )
( stack is the data stack. )
POSTPONE ELSE
R> ; ( we can bring count back now )
IMMEDIATE
: ENDCASE ( orig 1..orign #of -- )
POSTPONE DROP ( discard case value )
0 ?DO
POSTPONE THEN
LOOP ;
IMMEDIATE
--
Chuck Eaker / P.O. Box 8, K-1 3C12 / Schenectady, NY 12301 USA
eaker@crd.ge.com eaker@crdgw1.UUCP (518) 387-5964
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