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Make left recursion in pegs a failed parse 

Eventually left recursion will work fine, but this is prevents an infinite loop for now.
db4
Chris Double 2008-03-27 18:07:30 +13:00
parent 4c50daed22
commit 4e29081e93
2 changed files with 5 additions and 3 deletions
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4
extra/peg/peg-tests.factor
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@ -175,6 +175,8 @@ IN: peg.tests
[ "1" token , "+" token , "1" token , ] seq* , [ "1" token , "+" token , "1" token , ] seq* ,
] choice* ] choice*
"1-1" over parse parse-result-ast swap "1-1" over parse parse-result-ast swap
"1+1" swap parse parse-result-ast
] with-packrat ] with-packrat
[
"1+1" swap parse parse-result-ast
] with-packrat
] unit-test ] unit-test

4
extra/peg/peg.factor
View File

@ -34,12 +34,12 @@ GENERIC: (compile) ( parser -- quot )
#! that maps the input string position to the parser result. #! that maps the input string position to the parser result.
[ drop H{ } clone ] cache ; [ drop H{ } clone ] cache ;
: cached-result ( n input-cache input quot -- result ) :: cached-result ( n input-cache input quot -- result )
#! Get the cached result for input position n #! Get the cached result for input position n
#! from the input cache. If the item is not in the cache, #! from the input cache. If the item is not in the cache,
#! call 'quot' with 'input' on the stack to get the result #! call 'quot' with 'input' on the stack to get the result
#! and store that in the cache and return it. #! and store that in the cache and return it.
[ nip ] swap compose curry cache ; inline n input-cache [ drop input quot call ] cache ; inline
:: run-packrat-parser ( input quot c -- result ) :: run-packrat-parser ( input quot c -- result )
input input-from input input-from