patterns.sjs

var assert = require('chai').assert;

// Custom operators in `test` blocks:
//   =>= Deep equals
//   =!= Throws exception (lhs will be wrapped in a function)

describe 'Case patterns' {

  // Wildcard
  // --------
  
  it 'should match anything for wildcards' {
    function go {
      (1, 2) => 1,
      (1, *) => 2 
    }
    test 'match'    { go(1, 2) === 1 }
    test 'wildcard' { go(1, 5) === 2 }
  }

  // Literals
  // --------

  it 'should match literals' {
    function go {
      42        => 42,
      true      => true,
      'foo'     => 'foo',
      null      => null,
      undefined => undefined
    }
    test 'numbers'   { go(42) === 42 }
    test 'booleans'  { go(true) === true }
    test 'strings'   { go('foo') === 'foo' }
    test 'null'      { go(null) === null }
    test 'undefined' { go(undefined) === undefined }
  }

  // Builtins
  // --------

  it 'should match builtin types' {
    function go {
      Boolean   => 'boolean',
      NaN       => 'nan',
      Number    => 'number',
      String    => 'string',
      RegExp    => 'regexp',
      Date      => 'date',
      Array     => 'array',
      Object    => 'object',
      Function  => 'function',
      Math      => 'math'
    }
    test 'Boolean'   { go(true) === 'boolean' }
    test 'Nan'       { go(0/0) === 'nan' }
    test 'Number'    { go(42) === 'number' }
    test 'String'    { go('foo') === 'string' }
    test 'RegExp'    { go(/foo/) === 'regexp' }
    test 'Date'      { go(new Date()) === 'date' }
    test 'Array'     { go([]) === 'array' }
    test 'Object'    { go({}) === 'object' }
    test 'Function'  { go(go) === 'function' }
    test 'Math'      { go(Math) === 'math' }
  }

  // Identifiers
  // -----------

  it 'should match identifiers' {
    function go1 { x => x }
    function go2 { _x => _x }
    function go3 { $x => $x }
    test 'x'  { go1(1) === 1 }
    test '_x' { go2(2) === 2 }
    test '$x' { go3(3) === 3 }
  }

  // Binders
  // -------

  it 'should match binder patterns' {
    function go {
      x @ 1 => x,
      y @ String => y,
      z @ [1, 2, 3] => z
    }
    test 'literals' { go(1) === 1 }
    test 'types'    { go('foo') === 'foo' }
    test 'destruct' { go([1, 2, 3]) =>= [1, 2, 3] }
  }

  // Arrays
  // ------

  it 'should destructure array literals strictly' {
    function go {
      [x] => x,
      [*, x] => x,
      [*, *, x] => x
    }
    test 'length == 1' { go([1]) === 1 }
    test 'length == 2' { go([1, 2]) === 2 }
    test 'length == 3' { go([1, 2, 3]) === 3 }
    test 'no match'    { go([1, 2, 3, 4]) =!= TypeError }
  }

  it 'should collect array rest values' {
    function go1 {
      [...a, b, c] => [a, b, c]
    }
    function go2 {
      [a, ...b, c] => [a, b, c]
    }
    function go3 {
      [a, b, ...c] => [a, b, c]
    }
    test 'head' { go1([1, 2, 3, 4]) =>= [[1, 2], 3, 4] }
    test 'mid'  { go2([1, 2, 3, 4]) =>= [1, [2, 3], 4] }
    test 'tail' { go3([1, 2, 3, 4]) =>= [1, 2, [3, 4]] }
  }

  // Objects
  // -------

  it 'should destructure object literals loosely' {
    function go {
      { x: 1 }   => true,
      { 'a': 2 } => true
    }
    test 'only 1 key' { go({ x: 1 }) }
    test 'many keys'  { go({ x: 1, y: 2, z: 3 }) }
    test 'no keys'    { go({}) =!= TypeError }
    test 'string key' { go({ a: 2 }) }
  }

  it 'should bring object identifier keys into scope' {
    function go {
      { x, y, z } => x + y + z
    }
    test 'ident key' { go({ x: 'x', y: 'y', z: 'z' }) === 'xyz' }
  }

  it 'should bring object binder keys into scope' {
    function go {
      { a @ String } => a
    }
    test 'binder key' { go({ a: 'a' }) === 'a' }
    test 'binder key match error' { go({ a: 42 }) =!= TypeError }
  }

  it 'should check object for a key when using a plain key string' {
    function go {
      { 'x', y } => y
    }
    test 'key is there'   { go({ x: 1, y: 'y' }) === 'y' }
    test 'key isnt there' { go({ y: 'y' }) =!= TypeError }
  }

  it 'should box primitive values when destructuring objects' {
    function go {
      x @ { toString: Function } => x.toString()
    }
    test 'success' { go(42) === '42' }
  }

  // Extractors
  // ----------

  var Digits = {
    hasInstance: function {
      a @ Number if a < 1000 => true,
      * => false
    },
    unapply: function(x) {
      if (Digits.hasInstance(x)) {
        return Math.floor(x).toString().split('').map(parseFloat);
      }
    },
    unapplyObject: function(x) {
      var ds = Digits.unapply(x);
      if (ds) {
        return {
          hundreds: ds[0],
          tens: ds[1],
          ones: ds[2]
        };
      }
    }
  };

  var deep = {
    namespace: {
      Digits: Digits
    }
  };

  function Foo() {}


  it 'should call hasInstance for bare extractors' {
    function go {
      Digits => true,
      *      => false
    }
    test 'success' { go(100) }
    test 'failure' { !go(1001) }
  }

  it 'should fallback to instanceof for bare extractors' {
    function go {
      Foo => true,
      *   => false
    }
    test 'success' { go(new Foo()) }
    test 'failure' { !go(12) }
  }

  it 'should call unapply for array-like destructuring' {
    function go {
      Digits(h, t, o) => [h, t, o]
    }
    test 'success' { go(345) =>= [3, 4, 5] }
    test 'failure' { go(1001) =!= TypeError }
  }

  it 'should call unapplyObject for object-like destructuring' {
    function go {
      Digits{ hundreds: h, tens: t, ones: o } => [h, t, o]
    }
    test 'success' { go(345) =>= [3, 4, 5] }
    test 'failure' { go(1001) =!= TypeError }
  }

  it 'should call extractors within a deep namespace' {
    function go {
      deep.namespace.Digits => true
    }
    test 'success' { go(345) }
  }

  // Arguments
  // ---------

  it 'should allow multiple arguments' {
    function go {
      (x, y, z) => x + y + z
    }
    test 'success' { go('x', 'y', 'z') === 'xyz' }
  }

  it 'should match argument length loosely' {
    function go {
      (x, y, z) => x + y + z
    }
    test 'success' { go('x', 'y') === 'xyundefined' }
  }

  it 'should match unit strictly' {
    function go {
      () => true
    }
    test 'success' { go() }
    test 'failure' { go(1) =!= TypeError }
  }

  it 'should match on the first successful case when ambiguous' {
    function go {
      (a)    => 1,
      (a, b) => 2
    }
    test 'success' { go(1) === 1 }
  }

  it 'should collect rest argument values' {
    function go {
      (a, b, ...c) => [a, b, c]
    }
    test 'success' { go(1, 2, 3, 4) =>= [1, 2, [3, 4]] }
    test 'empty'   { go(1, 2) =>= [1, 2, []] }
  }

  // Rest Patterns
  // -------------

  it 'should map patterns when combined with rest' {
    function go {
      [...Number] => true,
      *           => false
    }
    test 'success' { go([1, 2, 3]) }
    test 'failure' { !go([1, 2, '3']) }
  }

  it 'should allow and collect nested rest patterns' {
    function go {
      [...[heads, ...tails]] => [heads, tails]
    }
    test 'success' {
      go([
        [1, 2, 3],
        [4, 5, 6],
        [7, 8, 9],
      ]) =>= [
        [1, 4, 7],
        [
          [2, 3],
          [5, 6],
          [8, 9],
        ]
      ]
    }
  }

  // Match keyword
  // -------------

  it 'should support match expressions' {
    function go(test) {
      return match test {
        x @ Number => x.toString(),
        * => null
      }
    }

    test 'success' { go(42) === '42' && go(true) === null }
  }

  it 'should preserve the lexical `this` context with match expressions' {
    var foo = {
      y: 42,
      go: function(x) {
        return match x {
          * => this.y
        }
      }
    };

    test 'success' { foo.go(1) === 42 }
  }

  it 'should support match statements' {
    function go(test) {
      var a;
      match test {
        case x @ Number: a = test;
        default:         a = null;
      }
      return a;
    }

    test 'success' { go(42) === 42 }
  }

  it 'should support early return in match statements' {
    function go(test) {
      match test {
        case x @ Number: return x;
        default:         null;
      }
      return 'foo';
    }

    test 'success' { go(42) === 42 && go('bar') === 'foo' }
  }

  it 'should support break/continue in match statements' {
    function go(test) {
      while (test < 10) {
        match test {
          case 1:
            test += 1;
            continue;
          case 2:
            test += 1;
            break;
        }
      }
      return test;
    }

    test 'success' { go(1) === 3 }
  }

  it 'should support the default keyword' {
    function go1 {
      1       => 2,
      default => 42,
    }

    function go2(x) {
      return match x {
        1       => 2,
        default => 42
      }
    }

    function go3(x) {
      match x {
        case 1:  return 2;
        default: return 42;
      }
    }

    test 'success 1' { go1(1) === 2 && go1(2) === 42 }
    test 'success 2' { go2(1) === 2 && go2(2) === 42 }
    test 'success 3' { go3(1) === 2 && go3(2) === 42 }
  }

  // Backtracking
  // ------------

  function Counter(c) {
    return {
      count: 0,
      unapply: function(x) {
        this.count += 1;
        var arr = [], i = c;
        while (i--) arr.unshift(i + 1);
        return arr;
      }
    }
  }

  it 'should backtrack in match expressions' {
    var C2 = Counter(2);
    var m = match null {
      C2(C2(1, 3), *) => 1,
      C2(C2(1, 2), *) => 2
    }

    test 'success' { C2.count === 2 && m === 2 }
  }

  it 'should backtrack in match statements' {
    var C2 = Counter(2);
    var m;

    match null {
      case C2(C2(1, 3), *): m = 1;
      case C2(C2(1, 2), *): m = 2;
    }

    test 'success' { C2.count === 2 && m === 2 }
  }

  it 'should work with complex patterns in match expressions' {
    function go(test) {
      return match test {
        ['black', ['red', ['red', a, x, b], y, c], z, d] => [1, a, x, b, y, c, z, d],
        ['black', ['red', a, x, ['red', b, y, c]], z, d] => [2, a, x, b, y, c, z, d],
        ['black', a, x, ['red', ['red', b, y, c], z, d]] => [3, a, x, b, y, c, z, d],
        ['black', a, x, ['red', b, y, ['red', c, z, d]]] => [4, a, x, b, y, c, z, d]
      }
    }

    test 'success 1' {
      go(['black', ['red', ['red', 1, 2, 3], 4, 5], 6, 7]) =>= [1, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 2' {
      go(['black', ['red', 1, 2, ['red', 3, 4, 5]], 6, 7]) =>= [2, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 3' {
      go(['black', 1, 2, ['red', ['red', 3, 4, 5], 6, 7]]) =>= [3, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 4' {
      go(['black', 1, 2, ['red', 3, 4, ['red', 5, 6, 7]]]) =>= [4, 1, 2, 3, 4, 5, 6, 7]
    }
  }

  it 'should work with complex patterns in match statements' {
    function go(test) {
      var r;
      match test {
        case ['black', ['red', ['red', a, x, b], y, c], z, d]: r = [1, a, x, b, y, c, z, d];
        case ['black', ['red', a, x, ['red', b, y, c]], z, d]: r = [2, a, x, b, y, c, z, d];
        case ['black', a, x, ['red', ['red', b, y, c], z, d]]: r = [3, a, x, b, y, c, z, d];
        case ['black', a, x, ['red', b, y, ['red', c, z, d]]]: r = [4, a, x, b, y, c, z, d];
      }
      return r;
    }

    test 'success 1' {
      go(['black', ['red', ['red', 1, 2, 3], 4, 5], 6, 7]) =>= [1, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 2' {
      go(['black', ['red', 1, 2, ['red', 3, 4, 5]], 6, 7]) =>= [2, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 3' {
      go(['black', 1, 2, ['red', ['red', 3, 4, 5], 6, 7]]) =>= [3, 1, 2, 3, 4, 5, 6, 7]
    }
    test 'success 4' {
      go(['black', 1, 2, ['red', 3, 4, ['red', 5, 6, 7]]]) =>= [4, 1, 2, 3, 4, 5, 6, 7]
    }
  }

  // Regressions
  // -----------

  it 'should preserve case order in lieu of grafting' {
    function go {
      (*,     false, true ) => 1,
      (false, true,  *    ) => 2,
      (*,     *,     false) => 3,
      (*,     *,     true ) => 4
    }
    test 'success' { go(false, true, false) === 2 }
  }

  it 'should concat backtrack nodes correctly' {
    function go(x, y) {
      match (x, y) {
        case (Foo, *): return 1;
        case (*, Foo): return 2;
      }
    }
    test 'success' { go(new Foo(), 1) === 1 && go(1, new Foo()) === 2 }
  }

  it 'should correctly clone syntax in guards' {
    function id(x) { return x }
    function go {
      x if x === id(x) => true,
      *                => false
    }
    test 'success' { go(1) === true }
  }

  it 'should match empty arrays' {
    function go {
      [] => true,
      *  => false
    }
    test 'success' { go([]) }
  }
}