new version of parser combinators
S. Doaitse Swierstra
Sat, 23 Jun 2001 10:31:57 +0200
We have been working hard on new versions of the Parser Combinators
and AG system, with the following improvements:
even better error repairs
much faster and simpler basic parsing machine
permutation (of different types) and list combinators
extensive reporting about repairs made and what was expected
the possibility to manipulate your own state during parsing
and result construction, using classed based (like monads) interfaces
As an example of the permutation combinators we parse a permutation
of three elements:
1) a list of 'a's
2) a 'b'
3) an optional 'c'
which is described by:
permtest :: Parser Char (String, Char, Char)
permtest = permute $ (,,) ~$~ pList (pSym 'a') ~*~ pSym 'b' ~*~ pOptSym 'c'
pOptSym :: Char -> Parser Char Char
pOptSym x = pSym x <|> pSucceed '_'
which we try on several inputs resulting in:
t permtest "acb"
t permtest "cdaa"
Symbol 'd' before 'a' was deleted, because 'b' or ('a')* was expected.
Symbol 'b' was inserted at end of file, because 'a' or 'b' was expected.
t permtest "abd"
Symbol 'd' at end of file was deleted, because 'c' or eof was expected.
t permtest ""
Symbol 'b' was inserted at end of file, because 'c' or 'b' or ('a')*
The manual is still of an earlier version and will be adapted soon.
As an example of the combinators we provide a parser for bibtex
files, that returns the repairs made to the erroneous entries (as
far as we understand the bibtex format).
I hope this is useful to you,