Fix minor bugs on statements

[taku0]

Problem 1: Conditions of if expressions are not type checked.

The following code should raise type error but not.

if 1 + 1 then 1 else 1

We must infer the type and unify it with Boolean type.

Problem 2: If expressions does not introduce new environment.

The following code

let x = true
if true then
  let x = 2
  1
else
  1

console.log(x + 1)

which is compiled into

var x = true;
(function() {
    if(true) {
        var x = 2;
        return 1;
    } else {
        return 1;
    }
})();
console.log((x + 1));

should raise type error, but not.

If expressions are compiled into function, so that they introduce new environments. Thus, we must also introduce new environments in the type inferer.

Problem 3: Missing \n after inits of do expression

The following code

let identityMonad = {
  return: \x -> x
  bind: \m f -> f m
}

do identityMonad
  let x = 1
  let y = 1
  z <- 1
  return 1

is compiled into

...

var __monad__ = identityMonad;
var x = 1
var y = 1return __monad__.bind(1, function(z) {

    return __monad__.return(1);
});

...

\n is missing after “var y = 1”.