A warmup exercise for a class

homework-0-calc.js

C.evalAST = function (ast) {
  var environment = {}

  function ev(ast) {
    return !Array.isArray(ast) ? ast : ops[ast[0]].apply(undefined, ast.slice(1))
  }

  var ops = {
    id  : function(x) {return environment.hasOwnProperty(x) ? environment[x] : 0},
    set : function(id, exp) {return environment[id] = ev(exp)},
    '+' : function(x, y) {return ev(x) + ev(y)},
    '-' : function(x, y) {return ev(x) - ev(y)},
    '*' : function(x, y) {return ev(x) * ev(y)},
    '/' : function(x, y) {return ev(x) / ev(y)},
    '^' : function(x, y) {return Math.pow(ev(x), ev(y))},
    seq : function(e1, e2) {ev(e1); return ev(e2)}
  }

  return ev(ast)
}