Portability | non-portable (uses existentially quantified data constructors) |
---|---|
Stability | stable |
Maintainer | athas@sigkill.dk |
This module implements permutation parsers, and is a generalisation
of Text.Parsec.Perm
that will work with any parser combinator
library. The algorithm is described in:
Parsing Permutation Phrases, by Arthur Baars, Andres Loh and Doaitse Swierstra.
- data PermParser p a
- permute :: (Alternative p, Monad p) => PermParser p a -> p a
- (<||>) :: PermParser p (a -> b) -> p a -> PermParser p b
- (<$$>) :: (a -> b) -> p a -> PermParser p b
- (<|?>) :: PermParser p (a -> b) -> (a, p a) -> PermParser p b
- (<$?>) :: (a -> b) -> (a, p a) -> PermParser p b
Documentation
data PermParser p a Source
The type PermParser p a
denotes a permutation parser that,
when converted by the permute
function, parses
s
streams with user state st
and returns a value of
type a
on success.
Normally, a permutation parser is first build with special operators
like (<||>
) and than transformed into a normal parser
using permute
.
permute :: (Alternative p, Monad p) => PermParser p a -> p aSource
The parser permute perm
parses a permutation of parser described
by perm
. For example, suppose we want to parse a permutation of:
an optional string of a
's, the character b
and an optional c
.
This can be described by:
test = permute (tuple <$?> ("",many1 (char 'a')) <||> char 'b' <|?> ('_',char 'c')) where tuple a b c = (a,b,c)
(<||>) :: PermParser p (a -> b) -> p a -> PermParser p bSource
The expression perm <||> p
adds parser p
to the permutation
parser perm
. The parser p
is not allowed to accept empty input -
use the optional combinator (<|?>
) instead. Returns a
new permutation parser that includes p
.
(<$$>) :: (a -> b) -> p a -> PermParser p 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 (<$?>
) instead.
If the function f
takes more than one parameter, the type variable
b
is instantiated to a functional type which combines nicely with
the adds parser p
to the (<||>
) combinator. This
results in stylized code where a permutation parser starts with a
combining function f
followed by the parsers. The function f
gets its parameters in the order in which the parsers are specified,
but actual input can be in any order.
(<|?>) :: PermParser p (a -> b) -> (a, p a) -> PermParser p bSource
The expression perm <||> (x,p)
adds parser p
to the
permutation parser perm
. The parser p
is optional - if it can
not be applied, the default value x
will be used instead. Returns
a new permutation parser that includes the optional parser p
.
(<$?>) :: (a -> b) -> (a, p a) -> PermParser p 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.