Safe Haskell	Safe-Inferred
Language	Haskell2010

Agda.Syntax.Parser.LookAhead

Contents

The LookAhead monad
Operations

Description

When lexing by hand (for instance string literals) we need to do some looking ahead. The LookAhead monad keeps track of the position we are currently looking at, and provides facilities to synchronise the look-ahead position with the actual position of the Parser monad (see sync and rollback).

Synopsis

data LookAhead a
runLookAhead :: (forall b. String -> LookAhead b) -> LookAhead a -> Parser a
lookAheadError :: String -> LookAhead a
getInput :: LookAhead AlexInput
setInput :: AlexInput -> LookAhead ()
liftP :: Parser a -> LookAhead a
nextChar :: LookAhead Char
eatNextChar :: LookAhead Char
sync :: LookAhead ()
rollback :: LookAhead ()
match :: [(String, LookAhead a)] -> LookAhead a -> LookAhead a
match' :: Char -> [(String, LookAhead a)] -> LookAhead a -> LookAhead a

The LookAhead monad

data LookAhead a Source #

The LookAhead monad is basically a state monad keeping with an extra AlexInput, wrapped around the Parser monad.

Instances

Instances details

Applicative LookAhead Source #
Instance details Defined in Agda.Syntax.Parser.LookAhead Methods pure :: a -> LookAhead a # (<>) :: LookAhead (a -> b) -> LookAhead a -> LookAhead b # liftA2 :: (a -> b -> c) -> LookAhead a -> LookAhead b -> LookAhead c # (>) :: LookAhead a -> LookAhead b -> LookAhead b # (<*) :: LookAhead a -> LookAhead b -> LookAhead a #
Functor LookAhead Source #
Instance details Defined in Agda.Syntax.Parser.LookAhead Methods fmap :: (a -> b) -> LookAhead a -> LookAhead b # (<$) :: a -> LookAhead b -> LookAhead a #
Monad LookAhead Source #
Instance details Defined in Agda.Syntax.Parser.LookAhead Methods (>>=) :: LookAhead a -> (a -> LookAhead b) -> LookAhead b # (>>) :: LookAhead a -> LookAhead b -> LookAhead b # return :: a -> LookAhead a #

runLookAhead :: (forall b. String -> LookAhead b) -> LookAhead a -> Parser a Source #

Run a LookAhead computation. The first argument is the error function.

Operations

lookAheadError :: String -> LookAhead a Source #

Throw an error message according to the supplied method.

getInput :: LookAhead AlexInput Source #

Get the current look-ahead position.

setInput :: AlexInput -> LookAhead () Source #

Set the look-ahead position.

liftP :: Parser a -> LookAhead a Source #

Lift a computation in the Parser monad to the LookAhead monad.

nextChar :: LookAhead Char Source #

Look at the next character. Fails if there are no more characters.

eatNextChar :: LookAhead Char Source #

Consume the next character. Does nextChar followed by sync.

sync :: LookAhead () Source #

Consume all the characters up to the current look-ahead position.

rollback :: LookAhead () Source #

Undo look-ahead. Restores the input from the ParseState.

match :: [(String, LookAhead a)] -> LookAhead a -> LookAhead a Source #

Do a case on the current input string. If any of the given strings match we move past it and execute the corresponding action. If no string matches, we execute a default action, advancing the input one character. This function only affects the look-ahead position.

match' :: Char -> [(String, LookAhead a)] -> LookAhead a -> LookAhead a Source #

Same as match but takes the initial character from the first argument instead of reading it from the input. Consequently, in the default case the input is not advanced.