Safe Haskell	None
Language	Haskell2010

FlatParse.Examples.BasicLambda.Lexer

Description

This module contains lexer and error message primitives for a simple lambda calculus parser. It demonstrates a simple but decently informative implementation of error message propagation.

Synopsis

data Expected
- = Msg String
- | Lit String
data Error
- = Precise Pos Expected
- | Imprecise Pos [Expected]
errorPos :: Error -> Pos
merge :: Error -> Error -> Error
type Parser = Parser Error
prettyError :: ByteString -> Error -> String
cut :: Parser a -> [Expected] -> Parser a
cut' :: Parser a -> Expected -> Parser a
runParser :: Parser a -> ByteString -> Result Error a
testParser :: Show a => Parser a -> String -> IO ()
lineComment :: Parser ()
multilineComment :: Parser ()
ws :: Parser ()
token :: Parser a -> Parser a
identStartChar :: Parser Char
identChar :: Parser Char
isKeyword :: Span -> Parser ()
symbol :: String -> Q Exp
symbol' :: String -> Q Exp
keyword :: String -> Q Exp
keyword' :: String -> Q Exp

Documentation

data Expected Source #

An expected item which is displayed in error messages.

Constructors

Msg String	An error message.
Lit String	A literal expected thing.

Instances

Instances details

Eq Expected Source #
Instance details Defined in FlatParse.Examples.BasicLambda.Lexer Methods (==) :: Expected -> Expected -> Bool # (/=) :: Expected -> Expected -> Bool #
Ord Expected Source #
Instance details Defined in FlatParse.Examples.BasicLambda.Lexer Methods compare :: Expected -> Expected -> Ordering # (<) :: Expected -> Expected -> Bool # (<=) :: Expected -> Expected -> Bool # (>) :: Expected -> Expected -> Bool # (>=) :: Expected -> Expected -> Bool # max :: Expected -> Expected -> Expected # min :: Expected -> Expected -> Expected #
Show Expected Source #
Instance details Defined in FlatParse.Examples.BasicLambda.Lexer Methods showsPrec :: Int -> Expected -> ShowS # show :: Expected -> String # showList :: [Expected] -> ShowS #
IsString Expected Source #
Instance details Defined in FlatParse.Examples.BasicLambda.Lexer Methods fromString :: String -> Expected #

data Error Source #

A parsing error.

Constructors

Precise Pos Expected	A precisely known error, like leaving out "in" from "let".
Imprecise Pos [Expected]	An imprecise error, when we expect a number of different things, but parse something else.

Instances

Instances details

Show Error Source #
Instance details Defined in FlatParse.Examples.BasicLambda.Lexer Methods showsPrec :: Int -> Error -> ShowS # show :: Error -> String # showList :: [Error] -> ShowS #

errorPos :: Error -> Pos Source #

merge :: Error -> Error -> Error Source #

Merge two errors. Inner errors (which were thrown at points with more consumed inputs) are preferred. If errors are thrown at identical input positions, we prefer precise errors to imprecise ones.

The point of prioritizing inner and precise errors is to suppress the deluge of "expected" items, and instead try to point to a concrete issue to fix.

type Parser = Parser Error Source #

prettyError :: ByteString -> Error -> String Source #

Pretty print an error. The ByteString input is the source file. The offending line from the source is displayed in the output.

cut :: Parser a -> [Expected] -> Parser a Source #

Imprecise cut: we slap a list of items on inner errors.

cut' :: Parser a -> Expected -> Parser a Source #

Precise cut: we propagate at most a single error.

runParser :: Parser a -> ByteString -> Result Error a Source #

testParser :: Show a => Parser a -> String -> IO () Source #

Run parser, print pretty error on failure.

lineComment :: Parser () Source #

Parse a line comment.