apply_rule: Applies the rule to the specified text

In mslegrand/pegr: PEG PARSER

Description

That is invoke the parser to parse a given input text using the specified rule as the root.

Usage

apply_rule(parser, rule.id, input.text, exe = NULL, record = NULL)

Arguments

parser,	a peg parser produced by new.parser
rule.id,	a character string naming the rule
arg,	a character string to be parsed
exe,	(optional, default=FALSE) a flag indicate whether actions should be performed. when FALSE, no actions will be executed
record,	(optional, default=FALSE) a flag which when set produces tree of snapshots of all nodes visited during a successful parse.

Value

A PEGResult, a container containing the status of the parsing attempt, a record of the characters parsed, and a list of one or more values computed during the parse. If exe not set (FALSE) or no actions have been attached to the rules, then the values will simply be a list of all literals (characters, or strings) that appeared in the input text.

Examples

# The simplest example: a parser that only accepts a single character 'a'
peg<-new.parser()
peg<-add_rule(peg, "A<-'a'")
res<-apply_rule(peg, 'A', "a")
res # the results

# A more complex example:
# A number parser: Extracts number
peg<-new.parser()
peg<-add_rule(peg, "NUM<-[0-9]+ ('.' [0-9]*)?)", act = "paste1(v)", des = "numbers")
apply_rule(peg, "NUM", "12.3", exe=T)
peg<-new.parser()
# rule set to convert distances to meters
peg<-add_rule(peg, "NUM<-[0-9]+ ('.' [0-9]*)?)", act = "list(  num=as.numeric(paste(v,collapse=''))  )", des = "numbers")
peg<-add_rule(peg, "IN<- NUM ' '* 'in' ", act="list( num=0.0254*v$num)", des="inches; ins 2 meters")
peg<-add_rule(peg, "FT<- NUM ' '* 'ft' ", act="list( num=0.3048*v$num)", des="feet; ft 2 meters")
peg<-add_rule(peg, "CM<- NUM ' '* 'cm' ", act="list( num=.01*v$num)", des="centimeters; cm 2 meters")
peg<-add_rule(peg, "M<- NUM ' '* 'm' ",  act="list(num=v$num)", des="meters; extract the num")
peg<-add_rule(peg, "SP<-(' ')", act="list()", des="spaces; eats spaces")
peg<-add_rule(peg, "GP<- (IN / FT / CM / M)", des="added for group t")
peg<-add_rule(peg, "LEN<-(GP SP+ LEN) / GP ", act="list(sum(unlist(v)))",  des="length; sum all the units" )

#first test the components
apply_rule(peg, "NUM", "3", exe=T)
apply_rule(peg, "IN", "1.0 in", exe=T)
apply_rule(peg, "FT", "2 ft", exe=T)
apply_rule(peg, "CM", "100 cm", exe=T)
apply_rule(peg, "M", "1 m", exe=T)
#now test together
apply_rule(peg, "LEN", "3 ft 3.3701 in", exe=T)
apply_rule(peg, "LEN", "3 m 4.8 cm", exe=T)
apply_rule(peg, "LEN",  "10 ft",exe=T)

mslegrand/pegr documentation built on May 23, 2019, 7:53 a.m.