JLambda/environments.js

/*
 * An environment is just an object that maps identifiers to JLambda expressions
 * with a few built-in (a standard Prelude environment)
 */

// returns the new environment after mutating it
// values = [(identifier, JLambda expression)]

var errors = require("./errors.js");
var rep = require("./representation.js");


function extend(env, values) {
  var new_env = {};
  var env_keys = Object.keys(env);
  for (var i = 0; i < env_keys.length; i++) {
    new_env[env_keys[i]] = env[env_keys[i]];
  }
  for (i = 0; i < values.length; i++) {
    new_env[values[i][0].val] = values[i][1];
  }
  return new_env;
}

// creates a new environment initialized with the pairs in values
function makeEnv(name, values) {
  var env = {};
  env.name = name;
  for (var i = 0; i < values.length; i++) {
    name = values[i][0].val;
    var val = values[i][1];
    env[name] = val;
  }
  return env;
}

function lookup(name, env) {
  var value = env[name];
  if (!value) {
    throw errors.UnboundError(name, env.name);
  }
  return value;
}

var prelude = makeEnv("prelude", [[new rep.Name("e"), new rep.FloatT(Math.E)],
                                  [new rep.Name("pi"), new rep.FloatT(Math.PI)]]);

var prelude_types = makeEnv("prelude_types",
                            [[new rep.Name("e"), new rep.TypeOp("Float", [], false)],
                            [new rep.Name("pi"), new rep.TypeOp("Float", [], false)]]);

module.exports = { prelude : prelude,
                   prelude_types : prelude_types,
                   lookup : lookup,
                   extend : extend };