Text.Parser.Expression

parsers-0.12.4: Parsing combinators

Copyright | (c) Edward Kmett 2011-2012 (c) Paolo Martini 2007 (c) Daan Leijen 1999-2001,
License | BSD-style (see the LICENSE file)
Maintainer | ekmett@gmail.com
Stability | experimental
Portability | non-portable
Safe Haskell | None
Language | Haskell2010

Text.Parser.Expression

Description

A helper module to parse "expressions". Builds a parser given a table of operators and associativities.

Synopsis

- data Assoc
  - = AssocNone
  - | AssocLeft
  - | AssocRight
- data Operator m a
  - = Infix (m (a -> a -> a)) Assoc
  - | Prefix (m (a -> a))
  - | Postfix (m (a -> a))
- type OperatorTable m a = [[Operator m a]]
- buildExpressionParser :: forall m a. (Parsing m, Applicative m) => OperatorTable m a -> m a -> m a

# Documentation

data Assoc #

This data type specifies the associativity of operators: left, right or none.

Constructors

AssocNone |
AssocLeft |
AssocRight |

Instances

Bounded Assoc # |
Methods minBound :: Assoc # maxBound :: Assoc #
Enum Assoc # |
Methods succ :: Assoc -> Assoc # pred :: Assoc -> Assoc # toEnum :: Int -> Assoc # fromEnum :: Assoc -> Int # enumFrom :: Assoc -> [Assoc] # enumFromThen :: Assoc -> Assoc -> [Assoc] # enumFromTo :: Assoc -> Assoc -> [Assoc] # enumFromThenTo :: Assoc -> Assoc -> Assoc -> [Assoc] #
Eq Assoc # |
Methods (==) :: Assoc -> Assoc -> Bool # (/=) :: Assoc -> Assoc -> Bool #
Data Assoc # |
Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Assoc -> c Assoc # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Assoc # toConstr :: Assoc -> Constr # dataTypeOf :: Assoc -> DataType # dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c Assoc) # dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Assoc) # gmapT :: (forall b. Data b => b -> b) -> Assoc -> Assoc # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Assoc -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Assoc -> r # gmapQ :: (forall d. Data d => d -> u) -> Assoc -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Assoc -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Assoc -> m Assoc # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Assoc -> m Assoc # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Assoc -> m Assoc #
Ord Assoc # |
Methods compare :: Assoc -> Assoc -> Ordering # (<) :: Assoc -> Assoc -> Bool # (<=) :: Assoc -> Assoc -> Bool # (>) :: Assoc -> Assoc -> Bool # (>=) :: Assoc -> Assoc -> Bool # max :: Assoc -> Assoc -> Assoc # min :: Assoc -> Assoc -> Assoc #
Read Assoc # |
Methods readsPrec :: Int -> ReadS Assoc # readList :: ReadS [Assoc] # readPrec :: ReadPrec Assoc # readListPrec :: ReadPrec [Assoc] #
Show Assoc # |
Methods showsPrec :: Int -> Assoc -> ShowS # show :: Assoc -> String # showList :: [Assoc] -> ShowS #
Ix Assoc # |
Methods range :: (Assoc, Assoc) -> [Assoc] # index :: (Assoc, Assoc) -> Assoc -> Int # unsafeIndex :: (Assoc, Assoc) -> Assoc -> Int inRange :: (Assoc, Assoc) -> Assoc -> Bool # rangeSize :: (Assoc, Assoc) -> Int # unsafeRangeSize :: (Assoc, Assoc) -> Int

data Operator m a #

This data type specifies operators that work on values of type `a`. An operator is either binary infix or unary prefix or postfix. A binary operator has also an associated associativity.

Constructors

Infix (m (a -> a -> a)) Assoc |
Prefix (m (a -> a)) |
Postfix (m (a -> a)) |

type OperatorTable m a = [[Operator m a]] #

An `OperatorTable m a` is a list of `Operator m a` lists. The list is ordered in descending precedence. All operators in one list have the same precedence (but may have a different associativity).

buildExpressionParser :: forall m a. (Parsing m, Applicative m) => OperatorTable m a -> m a -> m a #

`buildExpressionParser table term` builds an expression parser for terms `term` with operators from `table`, taking the associativity and precedence specified in `table` into account. Prefix and postfix operators of the same precedence can only occur once (i.e. `--2` is not allowed if `-` is prefix negate). Prefix and postfix operators of the same precedence associate to the left (i.e. if `++` is postfix increment, than `-2++` equals `-1`, not `-3`).

The `buildExpressionParser` takes care of all the complexity involved in building expression parser. Here is an example of an expression parser that handles prefix signs, postfix increment and basic arithmetic.

     import Control.Applicative ((<|>))
     import Text.Parser.Combinators ((<?>))
     import Text.Parser.Expression
     import Text.Parser.Token (TokenParsing, natural, parens, reserve)
     import Text.Parser.Token.Style (emptyOps)

     expr   :: (Monad m, TokenParsing m) => m Integer
     expr    = buildExpressionParser table term
             <?> "expression"

     term   :: (Monad m, TokenParsing m) => m Integer
     term    =  parens expr
             <|> natural
             <?> "simple expression"

     table  :: (Monad m, TokenParsing m) => [[Operator m Integer]]
     table   = [ [prefix "-" negate, prefix "+" id ]
               , [postfix "++" (+1)]
               , [binary "*" (*) AssocLeft, binary "/" (div) AssocLeft ]
               , [binary "+" (+) AssocLeft, binary "-" (-)   AssocLeft ]
               ]

     binary  name fun assoc = Infix (fun <$ reservedOp name) assoc
     prefix  name fun       = Prefix (fun <$ reservedOp name)
     postfix name fun       = Postfix (fun <$ reservedOp name)

     reservedOp name = reserve emptyOps name