I followed the online docs pretty closely and got hit by the fact that the
parser does not seem to always eat whitespace. If you run the following code,
you will see that the intergers have no whitespace, but the + does, which
causes the transform to fail. Any ideas of what I am doing wrong?
Thanks,
-Zach
---
require 'parslet'
class MiniP < Parslet::Parser
# Single character rules
rule(:lparen) { str('(') >> space? }
rule(:rparen) { str(')') >> space? }
rule(:comma) { str(',') >> space? }
rule(:space) { match('\s').repeat(1) }
rule(:space?) { space.maybe }
# Things
rule(:integer) { match('[0-9]').repeat(1).as(:int) >> space? }
rule(:identifier) { match['a-z'].repeat(1) }
rule(:operator) { match('[+]') >> space? }
# Grammar parts
rule(:sum) { integer.as(:left) >> operator.as(:op) >> expression.as(:right) }
rule(:arglist) { expression.as(:arg) >> (comma >> expression.as(:arg)).repeat
}
rule(:funcall) { identifier.as(:funcall) >> lparen >> arglist.as(:arglist) >>
rparen }
rule(:expression) { funcall | sum | integer }
root :expression
end
class MiniT < Parslet::Transform
rule(:int => simple(:x) ) { Integer(x) }
rule(:op => '+', :left => simple(:l), :right => simple(:r)) { l + r }
end
def parse(str)
mini = MiniP.new
tree = mini.parse(str)
print "Parsing #{str}: -> #{tree}\n"
result = MiniT.new.apply( tree )
print "Transform -> #{result}\n\n"
rescue Parslet::ParseFailed => error
puts error, mini.root.error_tree
end
parse "1 + 2"
#Parsing 1 + 2: -> {:left=>{:int=>"1"@0}, :op=>"+ "@2, :right=>{:int=>"2"@4}}
#Transform -> {:left=>1, :op=>"+ "@2, :right=>2}
parse "1+2"
#Parsing 1+2: -> {:left=>{:int=>"1"@0}, :op=>"+"@1, :right=>{:int=>"2"@2}}
#Transform -> 3
Zachary Drummond
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