lex: Build a lexer

In systemincloud/rly: Tools to Create Formal Language Parser

Build a lexer

Description

Build all of the regular expression rules from definitions in the supplied module

Usage

lex(module = NA, args = list(), debug = FALSE, debuglog = NA,
  errorlog = NA)

Arguments

module	R6 class containing lex rules
args	list of arguments that should be passed to constructor
debug	on and off debug mode
debuglog	custom logger for debug messages
errorlog	custom logger for error messages

Value

Lexer ready to use

Examples

TOKENS = c('NAME', 'NUMBER')
LITERALS = c('=','+','-','*','/', '(',')')

Lexer <- R6::R6Class("Lexer",
  public = list(
    tokens = TOKENS,
    literals = LITERALS,
    t_NAME = '[a-zA-Z_][a-zA-Z0-9_]*',
    t_NUMBER = function(re='\\d+', t) {
      t$value <- strtoi(t$value)
      return(t)
    },
    t_ignore = " \t",
    t_newline = function(re='\\n+', t) {
       t$lexer$lineno <- t$lexer$lineno + nchar(t$value)
       return(NULL)
    },
    t_error = function(t) {
      cat(sprintf("Illegal character '%s'", t$value[1]))
      t$lexer$skip(1)
      return(t)
    }
  )
)

lexer  <- rly::lex(Lexer)
lexer$input("5 + 3")
print(lexer$token()$value)
# [1] 5
print(lexer$token()$value)
# [1] "+"
print(lexer$token()$value)
# [1] 3

systemincloud/rly documentation built on May 11, 2022, 11:13 a.m.