yacc {rly} | R Documentation |
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)
[Package rly version 1.7.4 Index]