symbolic {qmrparser}

Alphanumeric token.

Description

Recognises an alphanumeric symbol. By default, a sequence of alphanumeric, numeric and dash symbols, beginning with an alphabetical character.

Usage

symbolic     (charFirst=isLetter,
              charRest=function(ch) isLetter(ch) || isDigit(ch) || ch == "-",
              action = function(s) list(type="symbolic",value=s), 
              error  = function(p) list(type="symbolic",pos  =p)) 

Arguments

charFirst

Predicate of valid characters as first symbol character

charRest

Predicate of valid characters as the rest of symbol characters

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

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

# fail
stream  <- streamParserFromString("123")
( symbolic()(stream) )[c("status","node")]

# ok 
stream  <- streamParserFromString("abc123_2")
( symbolic()(stream) )[c("status","node")]