Copyright | (c) Daan Leijen 1999-2001 (c) Paolo Martini 2007 |
---|---|
License | BSD-style (see the file libraries/parsec/LICENSE) |
Maintainer | derek.a.elkins@gmail.com |
Stability | provisional |
Portability | non-portable (uses existentially quantified data constructors) |
Safe Haskell | Safe |
Language | Haskell2010 |
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.
From the abstract:
A permutation phrase is a sequence of elements (possibly of different types) in which each element occurs exactly once and the order is irrelevant. Some of the permutable elements may be optional.
Synopsis
- 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
- (<$$>) :: Stream s Identity tok => (a -> b) -> Parsec s st a -> StreamPermParser s st b
- (<|?>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
- (<$?>) :: Stream s Identity tok => (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b
Documentation
type PermParser tok st a = StreamPermParser String st a Source #
Provided for backwards compatibility. The tok type is ignored.
data StreamPermParser s st a Source #
The type StreamPermParser s st a
denotes a permutation parser that,
when converted by the permute
function, parses
s
streams with user state st
and returns a value of
type a
on success.
Normally, a permutation parser is first build with special operators
like (<||>
) and than transformed into a normal parser
using permute
.
permute :: Stream s Identity tok => StreamPermParser s st a -> Parsec s st a Source #
The parser permute perm
parses a permutation of parser described
by perm
. For example, suppose we want to parse a permutation of:
an optional string of a
's, the character b
and an optional c
.
This can be described by:
test = permute (tuple <$?> ("",many1 (char 'a')) <||> char 'b' <|?> ('_',char 'c')) where tuple a b c = (a,b,c)
(<||>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> Parsec s st a -> StreamPermParser s st b infixl 1 Source #
The expression perm <||> p
adds parser p
to the permutation
parser perm
. The parser p
is not allowed to accept empty input -
use the optional combinator (<|?>
) instead. Returns a
new permutation parser that includes p
.
(<$$>) :: Stream s Identity tok => (a -> b) -> Parsec s st a -> StreamPermParser s st b infixl 2 Source #
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 (<$?>
) instead.
If the function f
takes more than one parameter, the type variable
b
is instantiated to a functional type which combines nicely with
the adds parser p
to the (<||>
) combinator. This
results in stylized code where a permutation parser starts with a
combining function f
followed by the parsers. The function f
gets its parameters in the order in which the parsers are specified,
but actual input can be in any order.
(<|?>) :: Stream s Identity tok => StreamPermParser s st (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b infixl 1 Source #
The expression perm <||> (x,p)
adds parser p
to the
permutation parser perm
. The parser p
is optional - if it can
not be applied, the default value x
will be used instead. Returns
a new permutation parser that includes the optional parser p
.
(<$?>) :: Stream s Identity tok => (a -> b) -> (a, Parsec s st a) -> StreamPermParser s st b infixl 2 Source #
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.