gistfile1.rb

require 'parslet'

class Butter < Parslet::Parser

	rule(:op_equals)  { str('=') >> space? }	
	rule(:let)        { str("let") >> space? }

	rule(:space)      { match('\s').repeat(1) }
	rule(:space?)     { space.maybe }
	
	rule(:integer)    { match('[0-9]').repeat(1).as(:int) >> space? }
	rule(:identifier) { (match['a-z'].repeat(1,1) >> match['a-zA-Z0-9_'].repeat).as(:id) }
		
	rule(:letexpr)	  { let >> identifier >> op_equals >> integer }

	root :letexpr
end

b = Butter.new
b.parse("let a1 = 1")
    


#C:/Ruby192/lib/ruby/gems/1.9.1/gems/parslet-1.2.3/lib/parslet/atoms/base.rb:257:in `parse_failed': Failed to match sequence (LET IDENTIFIER OP_EQUALS INTEGER) at line 1 char 6. (Parslet::ParseFailed)
#	from C:/Ruby192/lib/ruby/gems/1.9.1/gems/parslet-1.2.3/lib/parslet/atoms/base.rb:39:in `parse'
#	from C:/src/butterexample.rb:20:in `<main>'