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Ace case
The CASE structure is unfortunately omitted from Jupiter Ace Forth.This is an attempt to remedy that omission.
The 2 byte operand field of OF holds the number of bytes to be skipped to the corresponding ENDOF, if the, case isfalse.
The 2 byte operand field of ENDOF contains the number of bytes to be skipped to ENDCASE afterthe words between OF and ENDOF have been executed.
The numbers 7, 8,9 together with ?PAIRS are used to ensure that the CASE statement is always properly structured, in the form:
CASE (n- -)
x OF ... ENDOF
y OF ... ENDOF
z OF ... ENDOF
OTHERWISE ...
ENDCASE
OTHERWISE may not be omitted from the CASE statement.
Words containing the CASE structure may be EDITed and REDEFINEd, and they
may also be added to an existing directory.
The six words occupy 301 bytes as written, without comments.
: ?PAIRS
= 0=
IF
." ERROR 5"
CR ABORT
THEN
;
0 COMPILER CASE
0 9
RUNS>
DROP
;
2 COMPILER OF
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9 ?PAIRS
HERE 0,
7
RUNS>
>R OVER = R> SWAP
IF
DROP DROP
ELSE
@ R> + >R
THEN
;
2 COMPILER ENDOF
7 ?PAIRS
HERE SWAP 0,
OVER OVER - SWAP !
9
RUNS>
@ R> + >R
;
0 COMPILER OTHERWISE
9 ?PAIRS 8
RUNS
DROP DROP
;
0 COMPILER ENDCASE
8 ?PAIRS
BEGIN
?DUP
WHILE
HERE OVER - 2 -
SWAP !
REPEAT
RUNS>
DROP
;
Example use:
: SILLY ( n —)
CASE
1 OF CR ." NUMBER
ONE!" CR ENDOF
6 OF CR ." NUMBER
SIX!" CR ENDOF
40 OF CR ." NUMBER
FORTY!" CR ENDOF
OTHERWISE CR ." NOT
1, NOT 6, NOT 40 !" CR
ENDCASE
." The end of a pointless word." CR
;
Stephen Renals
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