A simple parser for parentheses implemented with delimited continuations using Consize

usedelco.txt

% A simple parser for parentheses implemented with delimited continuations
% using Consize, @denkspuren 2014-11-12 (Update)
%
% The implementation demonstrates parsing of brackets with delimited
% continuations. Since parentheses are already used in Consize,
% left and right parentheses are written as `((` and `))`, respectively.
%
% Take a program such as: `(( @A (( @B (( @C )) @D (( @E )) @F )) @G ))`;
% `@A `up to `@G` denote arbitrary code without any parentheses. As soon as
% word `((` is processed, `shift` starts looking for left and right
% parentheses in the code to come. Depending on the sequence of parentheses
% a corresponding stack is constructed. There are four situations reflecting
% two states of processing. On the right, the words to properly built the
% stack are shown. The following definition of `attach` comes in handy.

: attach ( [ @Stk ] #Itm -- [ @Stk #Itm ] ) ( ) cons concat ;
 
% 1. @X ( @Y (   
% 1. @X ( @Y )      attach
% 2. @X ) @Y (      concat
% 2. @X ) @Y )      concat attach 
%
% How does the parser know it's finished? We use a marker, word `!`, indicating
% when we are done.
%
% Since of no importance for demonstration purposes, the parser does not
% provide any means to pass words `((` and `))` literally on the stack.
%
% The code requires `\ delco.txt run` prior to executing this file.

: (( \ ! scan-brackets-open (( ;

: final-closing-bracket?
  over \ ! equal? [ nip top ] [ scan-brackets-closed ] if ;

: scan-brackets-open
  { \ (( [ scan-brackets-open ]
    \ )) [ attach final-closing-bracket? ]
  } shift ;

: scan-brackets-closed
  { \ (( [ concat scan-brackets-open ]
    \ )) [ concat attach final-closing-bracket? ]
  } shift ;

[     [ ]     ] [       (( ))       ] unit-test
[   [ [ ] ]   ] [    (( (( )) ))    ] unit-test
[ [ [ [ ] ] ] ] [ (( (( (( )) )) )) ] unit-test

[ [ 1     ] ] [ (( 1     )) ] unit-test
[ [ 1 2 3 ] ] [ (( 1 2 3 )) ] unit-test

[  [ [ 1 ] ]  ] [  (( (( 1 )) ))  ] unit-test
[ [ 1 [ 2 ] ] ] [ (( 1 (( 2 )) )) ] unit-test
[ [ [ 1 ] 2 ] ] [ (( (( 1 )) 2 )) ] unit-test
[ [ 1 [ 2 ] 3 ] ] [ (( 1 (( 2 )) 3 )) ] unit-test
[ [ 1 [ 2 ] [ 3 ] 4 ] ] [ (( 1 (( 2 )) (( 3 )) 4 )) ] unit-test
[ [ 1 [ 2 ] 3 [ 4 ] 5 ] ] [ (( 1 (( 2 )) 3 (( 4 )) 5 )) ] unit-test
[ [ 1 [ 2 [ [ 3 ] 4 ] ] 5 ] ] [ (( 1 (( 2 (( (( 3 )) 4 )) )) 5 )) ] unit-test

[ [ 3 2 1 ] 4 ] [ (( 1 2 3 )) reverse 4 ] unit-test