interp.rb

# $ ruby interp.rb test.rb
# test.rb
# plus_count=0
# x = 1+2+3
# p(plus_count) #=> 2
# x = 1+2+3
# p(plus_count) #=> 4


require "minruby"

def evaluate(tree, env)
  # pp(tree)
  case tree[0]
  when "lit"
    tree[1]
  when "+"
    evaluate(tree[1], env) + evaluate(tree[2], env)
    env["plus_count"] = env["plus_count"] +1
  when "-"
    evaluate(tree[1], env) - evaluate(tree[2], env)
  when "*"
    evaluate(tree[1], env) * evaluate(tree[2], env)
  when "/"
    evaluate(tree[1], env) / evaluate(tree[2], env)
  when "func_call"
    p(evaluate(tree[2], env))
  when "stmts"
    i = 1
    last = nil
    while tree[i] != nil
      last = evaluate(tree[i], env)
      i = i+1
    end
    last
  when "var_assign"
    env[tree[1]] = evaluate(tree[2], env)
  when "var_ref"
    env[tree[1]]
  end
end

str = minruby_load()

tree = minruby_parse(str)

env = {}
evaluate(tree, env)