retroforth/example/numbers-without-prefix.retro
crc 6a4aaf8eac prefix: namespace is now sigil:, rename words, update examples, update docs
FossilOrigin-Name: 25cf19660ab7728d7bfee2722ea826a8a438faf92b2504b28d922d2958906aed
2021-03-30 11:58:25 +00:00

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Forth

Numbers without the # Sigil
RETRO requires a # sigil to identify numbers. But since new
sigils can be defined, it's possible to define sigils for
the number starting with 0-9.
This is actually easy (at least for positive numbers). Just
define a sigil handler that prepends the initial value back
on the string (since the string sans the sigil is passed to
the handler) and pass it to `s:to-number` and `class:data`.
~~~
{{
:process-with-sigil (s-n)
s:prepend s:to-number class:data ;
---reveal---
:sigil:1 (s-n) '1 process-with-sigil ; immediate
:sigil:2 (s-n) '2 process-with-sigil ; immediate
:sigil:3 (s-n) '3 process-with-sigil ; immediate
:sigil:4 (s-n) '4 process-with-sigil ; immediate
:sigil:5 (s-n) '5 process-with-sigil ; immediate
:sigil:6 (s-n) '6 process-with-sigil ; immediate
:sigil:7 (s-n) '7 process-with-sigil ; immediate
:sigil:8 (s-n) '8 process-with-sigil ; immediate
:sigil:9 (s-n) '9 process-with-sigil ; immediate
~~~
`0` is a special case. Since RETRO has `0;` as a control
flow word, the `0` sigil would prevent using it. So the
handler for this checks to see if the part following the
sigil is a `;`. If so, it'll fall back to `0;`, otherwise
it treats the token as a number.
~~~
:sigil:0 (s-n)
dup '; s:eq?
[ drop &0; call ]
[ '0 process-with-sigil ] choose ; immediate
}}
~~~
For single digits, define each digit as a word. (Sigils
are not processed for tokens with nothing other than the
sigil character, so this takes care of the issue).
~~~
:0 (-n) #0 ;
:1 (-n) #1 ;
:2 (-n) #2 ;
:3 (-n) #3 ;
:4 (-n) #4 ;
:5 (-n) #5 ;
:6 (-n) #6 ;
:7 (-n) #7 ;
:8 (-n) #8 ;
:9 (-n) #9 ;
~~~
Handling negative numbers is a bigger headache though. By
convention, RETRO uses - to imply "not" (as in `-eq?`). So
to handle the `-` sigil for numbers, it needs to fall back
to a dictionary search if the token isn't actually a number.
~~~
{{
:numeric? (s-sf)
dup fetch c:digit? ;
:in-dictionary? (s-df)
'- s:prepend d:lookup dup n:zero? ;
:report-error (d-)
drop err:notfound ;
:call-with-class (d-)
[ d:xt fetch ] [ d:class fetch ] bi call ;
---reveal---
:sigil:- (s-)
numeric?
[ s:to-number n:negate class:data ]
[ in-dictionary? &report-error &call-with-class choose ] choose ; immediate
}}
~~~