Fix re-declaration semantics and refine generated code (close #49)

[chengluyu]

This PR fix #49 and add rename operations to Scope. Besides, this PR simplify and improve generated code.

Fix incorrect class name shadowing

Source MLscript

class Test: { x: int }
def Test x = Test { x }
def x = Test 0
def Test a = Test (a + 1)
def y = Test 0
def f Test = Test
def f x = 0

Generated JavaScript

(() => {
function prettyPrint(value) {
  switch (typeof value) {
    case "number":
    case "boolean":
    case "function":
      return value.toString();
    case "string":
      return '"' + value + '"';
    default:
      return value.constructor.name + " " + JSON.stringify(value, undefined, 2);
  }
}
const results = [];
class Test {
  constructor(fields) {
    this.x = fields.x;
  }
}
const Test1 = (x) => new Test({ x: x });
results.push(Test1);
const x = Test1(0);
results.push(x);
const Test2 = (a) => Test1(a + 1);
results.push(Test2);
const y = Test2(0);
results.push(y);
const f = (Test) => Test;
results.push(f);
const f1 = (x) => 0;
results.push(f1);
return results.map(prettyPrint);
})()

Translate pattern matches to ?:

Source MLscript

class A: { a: int }
class B: { b: int }

foo x = case x of { _ -> 1 }
foo x = case x of {
    | A -> x.a
    | _ -> 0
  }
def foo x = case id x of
  { A -> x.a
  | B -> x.b
  | _ -> 1
  }

Generated JavaScript

(() => {
// prettyPrint omitted
const results = [];
class A {
  constructor(fields) {
    this.a = fields.a;
  }
}
class B {
  constructor(fields) {
    this.b = fields.b;
  }
}
const foo = (x) => (x, 1);
results.push(foo);
const foo1 = (x) => (x instanceof A ? x.a : 0);
results.push(foo1);
const foo2 = (x) => {
  let temp;
  return temp = id(x), temp instanceof A ? x.a : temp instanceof B ? x.b : 1;
};
results.push(foo2);
return results.map(prettyPrint);
})()

Note that we cache the result with a temporary variable if there are more than two case branches in order to prevent duplicated evaluation.

[LPTK]

You implementation has at least one small oversight:

def f: (int & 'a) -> (int & 'a) -> 'a
def f a b = if gt a b then a else b

f 1 2

f x y = x

f 1 3

yields:

val f: (int & 'a) -> (int & 'a) -> 'a = (a) => (b) => a > b ? a : b
val f: (int & 'a) -> (int & 'a) -> 'a = (x) => (y) => x
val res: 1 | 2 = 2
val f: 'a -> anything -> 'a = no value
val res: 1 = 1

[chengluyu]

You implementation has at least one small oversight:

def f: (int & 'a) -> (int & 'a) -> 'a
def f a b = if gt a b then a else b

f 1 2

f x y = x

f 1 3

yields:

val f: (int & 'a) -> (int & 'a) -> 'a = (a) => (b) => a > b ? a : b
val f: (int & 'a) -> (int & 'a) -> 'a = (x) => (y) => x
val res: 1 | 2 = 2
val f: 'a -> anything -> 'a = no value
val res: 1 = 1

The output on my side is different from yours.

val f: (int & 'a) -> (int & 'a) -> 'a = (a) => (b) => (a > b ? a : b)
val f: (int & 'a) -> (int & 'a) -> 'a = 2
val res: 1 | 2 = (x) => (y) => x
val f: 'a -> anything -> 'a = 1
val res: 1 = no value

I just pushed the fix. Type check results and execution results should be aligned now.

[LPTK]

The example input in local_testing.html crashes with:

Runtime error occurred:
SyntaxError: Identifier 'temp' has already been declared

I minimized it to:

class Left[A]: { value: A }

def testVal = Left{ value = 1 }
def res = case testVal of
  { Left -> testVal.value
  }

PS: You should be doing these basic tests on your own, not wait that I do them myself.

[chengluyu]

The example input in local_testing.html crashes with:

Runtime error occurred:
SyntaxError: Identifier 'temp' has already been declared

I minimized it to:

class Left[A]: { value: A }

def testVal = Left{ value = 1 }
def res = case testVal of
  { Left -> testVal.value
  }

PS: You should be doing these basic tests on your own, not wait that I do them myself.

Thanks for pointing it out! I did not consider this case after introducing 8d6800f. I should try to keep this PR atomic. 😅

[LPTK]

Okay, this LGTM now. I think we should merge it.