Agda-2.3.2: A dependently typed functional programming language and proof assistant

Safe Haskell | None

Agda.Syntax.Parser.LexActions

Contents

- Main function
- Lex actions
  - General actions
  - Specialized actions
- Lex predicates

Description

This module contains the building blocks used to construct the lexer.

Synopsis

- lexToken :: Parser Token
- token :: (String -> Parser tok) -> LexAction tok
- withInterval :: ((Interval, String) -> tok) -> LexAction tok
- withInterval' :: (String -> a) -> ((Interval, a) -> tok) -> LexAction tok
- withInterval_ :: (Interval -> r) -> LexAction r
- withLayout :: LexAction r -> LexAction r
- begin :: LexState -> LexAction Token
- end :: LexAction Token
- endWith :: LexAction a -> LexAction a
- begin_ :: LexState -> LexAction Token
- end_ :: LexAction Token
- lexError :: String -> Parser a
- keyword :: Keyword -> LexAction Token
- symbol :: Symbol -> LexAction Token
- identifier :: LexAction Token
- literal :: Read a => (Range -> a -> Literal) -> LexAction Token
- followedBy :: Char -> LexPredicate
- eof :: LexPredicate
- inState :: LexState -> LexPredicate

# Main function

lexToken :: Parser Token

Scan the input to find the next token. Calls `alexScanUser`. This is the main lexing function where all the work happens. The function `lexer`, used by the parser is the continuation version of this function.

# Lex actions

## General actions

token :: (String -> Parser tok) -> LexAction tok

The most general way of parsing a token.

withInterval :: ((Interval, String) -> tok) -> LexAction tok

Parse a token from an `Interval` and the lexed string.

withInterval' :: (String -> a) -> ((Interval, a) -> tok) -> LexAction tok

Like `withInterval`, but applies a function to the string.

withInterval_ :: (Interval -> r) -> LexAction r

Return a token without looking at the lexed string.

withLayout :: LexAction r -> LexAction r

Executed for layout keywords. Enters the `layout` state and performs the given action.

begin :: LexState -> LexAction Token

Enter a new state without consuming any input.

end :: LexAction Token

Exit the current state without consuming any input

endWith :: LexAction a -> LexAction a

Exit the current state and perform the given action.

begin_ :: LexState -> LexAction Token

Enter a new state throwing away the current lexeme.

end_ :: LexAction Token

Exit the current state throwing away the current lexeme.

lexError :: String -> Parser a

For lexical errors we want to report the current position as the site of the error, whereas for parse errors the previous position is the one we're interested in (since this will be the position of the token we just lexed). This function does `parseErrorAt` the current position.

## Specialized actions

keyword :: Keyword -> LexAction Token

Parse a `Keyword` token, triggers layout for `layoutKeywords`.

symbol :: Symbol -> LexAction Token

Parse a `Symbol` token.

identifier :: LexAction Token

Parse an identifier. Identifiers can be qualified (see `Name`). Example: `Foo.Bar.f`

literal :: Read a => (Range -> a -> Literal) -> LexAction Token

Parse a literal.

# Lex predicates

followedBy :: Char -> LexPredicate

True when the given character is the next character of the input string.

eof :: LexPredicate

True if we are at the end of the file.

inState :: LexState -> LexPredicate

True if the given state appears somewhere on the state stack