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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/String-prepend/Forth/string-prepend.fth Normal file
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\ the following functions are commonly native to a Forth system. Shown for completeness
: C+! ( n addr -- ) dup c@ rot + swap c! ; \ primitive: increment a byte at addr by n
: +PLACE ( addr1 length addr2 -- ) \ Append addr1 length to addr2
2dup 2>r count + swap move 2r> c+! ;
: PLACE ( addr1 len addr2 -- ) \ addr1 and length, placed at addr2 as counted string
2dup 2>r 1+ swap move 2r> c! ;
\ Example begins here
: PREPEND ( addr len addr2 -- addr2)
>R \ push addr2 to return stack
PAD PLACE \ place the 1st string in PAD
R@ count PAD +PLACE \ append PAD with addr2 string
PAD count R@ PLACE \ move the whole thing back into addr2
R> ; \ leave a copy of addr2 on the data stack
: writeln ( addr -- ) cr count type ; \ syntax sugar for testing