yacc: Build a parser

In rly: Tools to Create Formal Language Parser

Build a parser

Description

This function is entry point to the library

Usage

yacc(module = NA, args = list(), method = "LALR", debug = FALSE,
  start = NA, check_recursion = TRUE, debugfile = "parser.out",
  outputdir = NA, debuglog = NA, errorlog = NA)

Arguments

module	R6 class containing rules
args	list of arguments that should be passed to constructor
method	type of algorithm
debug	on and off debug mode
start	provide custom start method
check_recursion	should yacc look for recursions in rules
debugfile	the name of the custom debug output logs
outputdir	the dierectory of custom debug logs
debuglog	custom logger for debug messages
errorlog	custom logger for error messages

Value

Parser ready to use

Examples

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

Parser <- R6::R6Class("Parser",
  public = list(
    tokens = TOKENS,
    literals = LITERALS,
    # Parsing rules
    precedence = list(c('left','+','-'),
                      c('left','*','/'),
                      c('right','UMINUS')),
    # dictionary of names
    names = new.env(hash=TRUE),
    p_statement_assign = function(doc='statement : NAME "=" expression', p) {
      self$names[[as.character(p$get(2))]] <- p$get(4)
    },
    p_statement_expr = function(doc='statement : expression', p) {
      cat(p$get(2))
      cat('\n')
    },
    p_expression_binop = function(doc="expression : expression '+' expression
                                                  | expression '-' expression
                                                  | expression '*' expression
                                                  | expression '/' expression", p) {
      if(p$get(3) == '+') p$set(1, p$get(2) + p$get(4))
      else if(p$get(3) == '-') p$set(1, p$get(2) - p$get(4))
      else if(p$get(3) == '*') p$set(1, p$get(2) * p$get(4))
      else if(p$get(3) == '/') p$set(1, p$get(2) / p$get(4))
    },
    p_expression_uminus = function(doc="expression : '-' expression %prec UMINUS", p) {
      p$set(1, -p$get(3))
    },
    p_expression_group = function(doc="expression : '(' expression ')'", p) {
      p$set(1, p$get(3))
    },
    p_expression_number = function(doc='expression : NUMBER', p) {
      p$set(1, p$get(2))
    },
    p_expression_name = function(doc='expression : NAME', p) {
      p$set(1, self$names[[as.character(p$get(2))]])
    },
    p_error = function(p) {
      if(is.null(p)) cat("Syntax error at EOF")
      else           cat(sprintf("Syntax error at '%s'", p$value))
    }
  )
)

parser <- rly::yacc(Parser)

rly documentation built on May 8, 2022, 5:05 p.m.