Class: Purple::SexpVM

Inherits:
Object
  • Object
show all
Defined in:
lib/purple/sexp_vm.rb

Instance Method Summary collapse

Constructor Details

#initialize ⇒ SexpVM

Returns a new instance of SexpVM.



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# File 'lib/purple/sexp_vm.rb', line 6

def initialize
  @vars = {}
end

Instance Method Details

#evaluate(sexp) ⇒ Object 



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# File 'lib/purple/sexp_vm.rb', line 10

def evaluate(sexp)
  f, *args = *sexp
#ap "x"*80
#ap f.inspect
#ap args.inspect
  ret =case f
  when :program
   # TODO: eliminate redundant array surrounding each expr
   ret = nil
   args.each { |stmt| ret = evaluate stmt.first }
   ret
  when :assign
    raise 'huh?' unless args.length == 2
    ident, expr = args.first, args.last
    name = ident.last
    @vars[name] = evaluate expr
  when :int
    raise 'huh?' unless args.length == 1
    args.first
  when :+
    raise 'huh?' unless args.length == 2
    evaluate(args.first) + evaluate(args.last)
  when :-
    raise 'huh?' unless args.length == 2
    evaluate(args.first) - evaluate(args.last)
  when :*
    raise 'huh?' unless args.length == 2
    evaluate(args.first) * evaluate(args.last)
  when :/
    raise 'huh?' unless args.length == 2
    evaluate(args.first) / evaluate(args.last)
  when :ident
    @vars[args.first]
  else
    raise "unknown sexp op: #{f}"
  end
end