empty: Empty token

In qmrparser: Parser Combinator in R

Empty token

Description

Recognises a null token. This parser always succeeds.

Usage

  
  empty(action = function(s) list(type="empty",value=s), 
        error  = function(p) list(type="empty",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

action s parameter is always "". Error parameters exists for the sake of homogeneity with the rest of functions. It is not used.

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")
( empty()(stream) )[c("status","node")]

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

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