FlatParse.Examples.BasicLambda.Lexer

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.

Documentation

data Expected

An expected item which is displayed in error messages.

Constructors

Msg String

An error message.

Lit String

A literal expected thing.

Instances

Eq Expected

Defined in FlatParse.Examples.BasicLambda.Lexer

Methods

(==) :: Expected -> Expected -> Bool

(/=) :: Expected -> Expected -> Bool

Ord Expected

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

Defined in FlatParse.Examples.BasicLambda.Lexer

Methods

showsPrec :: Int -> Expected -> ShowS

show :: Expected -> String

showList :: [Expected] -> ShowS

IsString Expected

Defined in FlatParse.Examples.BasicLambda.Lexer

Methods

fromString :: String -> Expected

data Error

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

Show Error

Defined in FlatParse.Examples.BasicLambda.Lexer

Methods

showsPrec :: Int -> Error -> ShowS

show :: Error -> String

showList :: [Error] -> ShowS

errorPos :: Error -> Pos

merge :: Error -> Error -> Error

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

prettyError :: ByteString -> Error -> String

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

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

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

Precise cut: we propagate at most a single error.

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

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

Run parser, print pretty error on failure.

lineComment :: Parser ()

Parse a line comment.

multilineComment :: Parser ()

Parse a potentially nested multiline comment.

ws :: Parser ()

Consume whitespace.

token :: Parser a -> Parser a

Consume whitespace after running a parser.

identStartChar :: Parser Char

Read a starting character of an identifier.

identChar :: Parser Char

Read a non-starting character of an identifier.

isKeyword :: Span -> Parser ()

Check whether a Span contains exactly a keyword. Does not change parsing state.

symbol :: String -> Q Exp

Parse a non-keyword string.

symbol' :: String -> Q Exp

Parser a non-keyword string, throw precise error on failure.

keyword :: String -> Q Exp

Parse a keyword string.

keyword' :: String -> Q Exp

Parse a keyword string, throw precise error on failure.