| Portability | non-portable (uses existentially quantified data constructors) |
|---|---|
| Stability | provisional |
| Maintainer | derek.a.elkins@gmail.com |
| Safe Haskell | Safe-Inferred |
Text.Parsec.Perm
Description
This module implements permutation parsers. The algorithm used is fairly complex since we push the type system to its limits :-) The algorithm is described in:
Parsing Permutation Phrases, by Arthur Baars, Andres Loh and Doaitse Swierstra. Published as a functional pearl at the Haskell Workshop 2001.
- type PermParser tok st a = StreamPermParser String st a
- data StreamPermParser s st a
- permute :: Stream s Identity tok => StreamPermParser s st a -> Parsec s st a
- (<||>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> Parsec s st a -> StreamPermParser s st b
- (<$$>) :: Stream s Identity tok => (a -> b) -> Parsec s st a -> StreamPermParser s st b
- (<|?>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
- (<$?>) :: Stream s Identity tok => (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
Documentation
type PermParser tok st a = StreamPermParser String st aSource
Provided for backwards compatibility. The tok type is ignored.
data StreamPermParser s st a Source
The type StreamPermParser s st a denotes a permutation parser that,
when converted by the permute function, parses
s streams with user state st and returns a value of
type a on success.
Normally, a permutation parser is first build with special operators
like (<||>) and than transformed into a normal parser
using permute.
permute :: Stream s Identity tok => StreamPermParser s st a -> Parsec s st aSource
The parser permute perm parses a permutation of parser described
by perm. For example, suppose we want to parse a permutation of:
an optional string of a's, the character b and an optional c.
This can be described by:
test = permute (tuple <$?> ("",many1 (char 'a'))
<||> char 'b'
<|?> ('_',char 'c'))
where
tuple a b c = (a,b,c)
(<||>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> Parsec s st a -> StreamPermParser s st bSource
The expression perm <||> p adds parser p to the permutation
parser perm. The parser p is not allowed to accept empty input -
use the optional combinator (<|?>) instead. Returns a
new permutation parser that includes p.
(<$$>) :: Stream s Identity tok => (a -> b) -> Parsec s st a -> StreamPermParser s st bSource
The expression f <$$> p creates a fresh permutation parser
consisting of parser p. The the final result of the permutation
parser is the function f applied to the return value of p. The
parser p is not allowed to accept empty input - use the optional
combinator (<$?>) instead.
If the function f takes more than one parameter, the type variable
b is instantiated to a functional type which combines nicely with
the adds parser p to the (<||>) combinator. This
results in stylized code where a permutation parser starts with a
combining function f followed by the parsers. The function f
gets its parameters in the order in which the parsers are specified,
but actual input can be in any order.
(<|?>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st bSource
The expression perm <||> (x,p) adds parser p to the
permutation parser perm. The parser p is optional - if it can
not be applied, the default value x will be used instead. Returns
a new permutation parser that includes the optional parser p.
(<$?>) :: Stream s Identity tok => (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st bSource
The expression f <$?> (x,p) creates a fresh permutation parser
consisting of parser p. The the final result of the permutation
parser is the function f applied to the return value of p. The
parser p is optional - if it can not be applied, the default value
x will be used instead.