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SassMeister-input.scss

// ----
// Sass (v3.4.5)
// Compass (v1.0.1)
// ----

// Sass BDD syntax proposal
// ========================
// - based on [Jasmine](http://jasmine.github.io/2.0/introduction.html)
// - comparitor may be easier to parse with dashes e.g. "not-to-be"
// - simplest parsing would use commas as well e.g. "expect($foo, to equal, 1)"
// - describe/it/expect seems parallel to TDD module/test/assert
// - if so, True could impliment both syntaxes over the same logic


// Pseudo Code!
// ------------

@function list-slice($list, $start: 1, $end: length($list), $sep:'comma') {
  $result: null;
  @if type-of($start) != number or type-of($end) != number {
    @warn "Either $start or $end are not a number for `slice`.";
  }
  @else if $start > $end {
    @warn "The start index has to be lesser than or equals to the end index for `slice`.";
  }

  @else if $start < 1 or $end < 1 {
    @warn "List indexes must be non-zero integers for `slice`.";
  }

  @else if $start > length($list) {
    @warn "List index is #{$start} but list is only #{length($list)} item long for `slice`.";
  }
  @else if $end > length($list) {
    @warn "List index is #{$end} but list is only #{length($list)} item long for `slice`.";
  }
  @else {
    $result: ();
    @for $i from $start through $end {
      $result: append($result, nth($list, $i), $sep);
    }
  }

  @return $result;
}

@function be-matcher($list) {
  /* be-matcher - #{$list} */
  @return "be-matcher";
}

@function equal-matcher($list) {
  /* equal-matcher - #{$list} */
  @return "equal-matcher";
}

@function look-ahead($list, $current-index, $places-ahead) {
  $index : $current-index - $places-ahead;
  @if $index <= 0 { $index : 1; }
  @return nth($list, $index);
}

@function scan-expects($list) {
  @each $value in $list {
   @if $value eq 'to' {
     $index : index($list, $value);
     $matcher : look-ahead($list, $index, 1);
     @if function_exists("#{$matcher}-matcher") {
       $remaining-args : list-slice($list, $index);
       $foo : call("#{$matcher}-matcher", $list);
       @return $foo;
     }
   }
 }
 @return "no matcher";
}

@mixin describe($desc){ 
  /* 
  /* #{$desc} */
  @content
}

@mixin it($desc){
  /* - #{$desc} */
  @content 
}

@mixin expect($test){
  /* -- EXPECT: #{$test} */
  $foo : scan-expects($test);
  /* --Matcher: #{$foo} */
  @content 
}


// USAGE
// -----

@include describe("A suite") {
  @include it("contains spec with an expectation") {
    @include expect(true to be true);
  }
}

@include describe("The 'toBe' matcher compares with ===") {
  @include it("and has a positive case") {
    @include expect(true to be true);
  }

  @include it("and can have a negative case") {
    @include expect(false not to be true);
  }
}

@include describe("A spec") {
  @include it("is just a function, so it can contain any code") {
    $foo: 0;
    $foo: $foo + 1;

    @include expect($foo to equal 1);
  }

  @include it("can have more than one expectation") {
    $foo: 0;
    $foo: $foo + 1;

    @include expect($foo to equal 1);
    @include expect(true to equal true);
    @include expect(12 to be gte 9);
    @include expect(12 to be '>=' 9);
  }
}

SassMeister-output.css

/* 
/* A suite */
/* - contains spec with an expectation */
/* -- EXPECT: true to be true */
/* --Matcher: no matcher */
/* 
/* The 'toBe' matcher compares with === */
/* - and has a positive case */
/* -- EXPECT: true to be true */
/* --Matcher: no matcher */
/* - and can have a negative case */
/* -- EXPECT: false false be true */
/* --Matcher: be-matcher */
/* 
/* A spec */
/* - is just a function, so it can contain any code */
/* -- EXPECT: 1 to equal 1 */
/* --Matcher: no matcher */
/* - can have more than one expectation */
/* -- EXPECT: 1 to equal 1 */
/* --Matcher: no matcher */
/* -- EXPECT: true to equal true */
/* --Matcher: no matcher */
/* -- EXPECT: 12 to be gte 9 */
/* --Matcher: be-matcher */
/* -- EXPECT: 12 to be >= 9 */
/* --Matcher: be-matcher */