whitespace: White sequence token.

In qmrparser: Parser Combinator in R

White sequence token.

Description

Recognises a white character sequence (this sequence may be empty).

Usage

  whitespace(action = function(s) list(type="white",value=s), 
             error  = function(p) list(type="white",pos  =p) ) 

Arguments

action	Function to be executed if recognition succeeds. Character stream making up the token is passed as parameter to this function
error	Function to be executed if recognition does not succeed. Position of streamParser obtained with streamParserPosition is passed as parameter to this function

Details

A character is considered a white character when function isWhitespace returns TRUE

Value

Anonymous function, returning a list.

function(stream) –> list(status,node,stream)

From input parameters, an anonymous function is defined. This function admits just one parameter, stream, with type streamParser, and returns a three-field list:

• status

  "ok" or "fail"

• node

  With action or error function output, depending on the case

• stream

  With information about the input, after success or failure in recognition

Examples

# ok
stream  <- streamParserFromString("Hello world")
( whitespace()(stream) )[c("status","node")]

# ok
stream  <- streamParserFromString(" Hello world")
( whitespace()(stream) )[c("status","node")]

# ok 
stream  <- streamParserFromString("")
(  whitespace()(stream) )[c("status","node")]

qmrparser documentation built on April 24, 2022, 1:05 a.m.