Returns the current source position. See also SourcePos.

Returns the current input

Returns the current user state.

putState st set the user state to st.

modifyState f applies function f to the user state. Suppose that we want to count identifiers in a source, we could use the user state as:

 expr  = do{ x <- identifier
           ; modifyState (+1)
           ; return (Id x)
           }

A synonym for <?>, but as a function instead of an operator.

choice ps tries to apply the parsers in the list ps in order, until one of them succeeds. Returns the value of the succeeding parser.

many1 p applies the parser p one or more times. Returns a list of the returned values of p.

 word  = many1 letter

skipMany1 p applies the parser p one or more times, skipping its result.

count n p parses n occurrences of p. If n is smaller or equal to zero, the parser equals to return []. Returns a list of n values returned by p.

between open close p parses open, followed by p and close. Returns the value returned by p.

 braces  = between (symbol "{") (symbol "}")

option x p tries to apply parser p. If p fails without consuming input, it returns the value x, otherwise the value returned by p.

 priority  = option 0 (do{ d <- digit
                         ; return (digitToInt d) 
                         })

optionMaybe p tries to apply parser p. If p fails without consuming input, it return Nothing, otherwise it returns Just the value returned by p.

optional p tries to apply parser p. It will parse p or nothing. It only fails if p fails after consuming input. It discards the result of p.

sepBy p sep parses zero or more occurrences of p, separated by sep. Returns a list of values returned by p.

 commaSep p  = p `sepBy` (symbol ",")

sepBy1 p sep parses one or more occurrences of p, separated by sep. Returns a list of values returned by p.

endBy p sep parses zero or more occurrences of p, separated and ended by sep. Returns a list of values returned by p.

  cStatements  = cStatement `endBy` semi

endBy1 p sep parses one or more occurrences of p, separated and ended by sep. Returns a list of values returned by p.

sepEndBy p sep parses zero or more occurrences of p, separated and optionally ended by sep, ie. haskell style statements. Returns a list of values returned by p.

 haskellStatements  = haskellStatement `sepEndBy` semi

sepEndBy1 p sep parses one or more occurrences of p, separated and optionally ended by sep. Returns a list of values returned by p.

chainl p op x parses zero or more occurrences of p, separated by op. Returns a value obtained by a left associative application of all functions returned by op to the values returned by p. If there are zero occurrences of p, the value x is returned.

chainl1 p op x parses one or more occurrences of p, separated by op Returns a value obtained by a left associative application of all functions returned by op to the values returned by p. . This parser can for example be used to eliminate left recursion which typically occurs in expression grammars.

 expr    = term   `chainl1` addop
 term    = factor `chainl1` mulop
 factor  = parens expr <|> integer

 mulop   =   do{ symbol "*"; return (*)   }
         <|> do{ symbol "/"; return (div) }

 addop   =   do{ symbol "+"; return (+) }
         <|> do{ symbol "-"; return (-) }

chainr p op x parses zero or more occurrences of p, separated by op Returns a value obtained by a right associative application of all functions returned by op to the values returned by p. If there are no occurrences of p, the value x is returned.

chainr1 p op x parses one or more occurrences of |p|, separated by op Returns a value obtained by a right associative application of all functions returned by op to the values returned by p.

This parser only succeeds at the end of the input. This is not a primitive parser but it is defined using notFollowedBy.

 eof  = notFollowedBy anyToken <?> "end of input"

notFollowedBy p only succeeds when parser p fails. This parser does not consume any input. This parser can be used to implement the 'longest match' rule. For example, when recognizing keywords (for example let), we want to make sure that a keyword is not followed by a legal identifier character, in which case the keyword is actually an identifier (for example lets). We can program this behaviour as follows:

 keywordLet  = try (do{ string "let"
                      ; notFollowedBy alphaNum
                      })

manyTill p end applies parser p zero or more times until parser end succeeds. Returns the list of values returned by p. This parser can be used to scan comments:

 simpleComment   = do{ string "<!--"
                     ; manyTill anyChar (try (string "-->"))
                     }

Note the overlapping parsers anyChar and string "-->", and therefore the use of the try combinator.

The parser anyToken accepts any kind of token. It is for example used to implement eof. Returns the accepted token.

The abstract data type ParseError represents parse errors. It provides the source position (SourcePos) of the error and a list of error messages (Message). A ParseError can be returned by the function parse. ParseError is an instance of the Show and Eq classes.

Extracts the source position from the parse error

The abstract data type SourcePos represents source positions. It contains the name of the source (i.e. file name), a line number and a column number. SourcePos is an instance of the Show, Eq and Ord class.

Extracts the name of the source from a source position.

Extracts the line number from a source position.

Extracts the column number from a source position.

Increments the line number of a source position.

Increments the column number of a source position.

Set the line number of a source position.

Set the column number of a source position.

Set the name of the source.

Returns the full parser state as a State record.

setParserState st set the full parser state to st.

updateParserState f applies function f to the parser state.

An instance of Stream has stream type s, underlying monad m and token type t determined by the stream

Some rough guidelines for a "correct" instance of Stream:

• unfoldM uncons gives the [t] corresponding to the stream
• A Stream instance is responsible for maintaining the "position within the stream" in the stream state s. This is trivial unless you are using the monad in a non-trivial way.

Low-level creation of the ParsecT type. You really shouldn't have to do this.

setPosition pos sets the current source position to pos.

setInput input continues parsing with input. The getInput and setInput functions can for example be used to deal with #include files.

An alias for putState for backwards compatibility.

An alias for modifyState for backwards compatibility.