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 }} ~~~