parsers-0.12.11: 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 | Safe-Inferred
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

Instances details

Data Assoc # |

Instance details

Defined in Text.Parser.Expression

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 :: forall r r'. (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

Bounded Assoc # |
Instance details Defined in Text.Parser.Expression Methods minBound :: Assoc maxBound :: Assoc
Enum Assoc # |
Instance details Defined in Text.Parser.Expression 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]
Ix Assoc # |
Instance details Defined in Text.Parser.Expression 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
Read Assoc # |
Instance details Defined in Text.Parser.Expression Methods readsPrec :: Int -> ReadS Assoc readList :: ReadS [Assoc] readPrec :: ReadPrec Assoc readListPrec :: ReadPrec [Assoc]
Show Assoc # |
Instance details Defined in Text.Parser.Expression Methods showsPrec :: Int -> Assoc -> ShowS show :: Assoc -> String showList :: [Assoc] -> ShowS
Eq Assoc # |
Instance details Defined in Text.Parser.Expression Methods (==) :: Assoc -> Assoc -> Bool (/=) :: Assoc -> Assoc -> Bool
Ord Assoc # |
Instance details Defined in Text.Parser.Expression 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

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