vidarh / writing-a-compiler-in-ruby

Code from my series on writing a Ruby compiler in Ruby

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writing-a-compiler-in-ruby / sexp.rb
100644 31 lines (24 sloc) 0.486 kb
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require 'parserbase'
 
# Simple Recursive-Descent s-expression parser
class SEXParser < ParserBase
 
  def initialize(scanner)
    super(scanner)
  end
 
  def parse
    expect("%s") or return
    parse_sexp or expected("s-expression")
  end
 
  def parse_sexp
    expect("(") or return
    ws
    exprs = zero_or_more(:exp)
    expect(")") or expected("')'")
    return exprs
  end
 
  def parse_exp
    ws
    ret = expect(Atom, Int, Quoted) || parse_sexp
    ws
    return ret
  end
end