`Gulp watch` yields errors related to code between `/*` and `*/` in my `scss` file, although I've read that this is a regular way of commenting in `SASS`. Any idea why I have this problem?

[EDIT] 
Error:

```
Error: Undefined variable: "$sm-breakpoint".
        on line 42 of assets/styles/core/_media-queries.scss
>> /*
   ^
[23:30:48] Finished 'styles' after 14 ms

```

Content of my `scss` file:

```
$screen: "only screen";
$landscape: "#{$screen} and (orientation: landscape)";
$portrait: "#{$screen} and (orientation: portrait)";

/* Breakpoints */
$mq_600: "#{$screen} and (max-width: 600px)";
$mq_768: "#{$screen} and (max-width: 768px)";
$mq_1000: "#{$screen} and (max-width: 1000px)";
$mq_1024: "#{$screen} and (max-width: 1023px)";
$mq_1200: "#{$screen} and (max-width: 1200px)";
$mq_1300: "#{$screen} and (max-width: 1300px)";
$mq_1400: "#{$screen} and (max-width: 1400px)";
$mq_1500: "#{$screen} and (max-width: 1500px)";
$mq_1460: "#{$screen} and (max-width: 1460px)";

@mixin mq_600 {
  @media #{$mq_600} {@content}
}
@mixin mq_768 {
  @media #{$mq_768} {@content}
}
@mixin mq_1000 {
  @media #{$mq_1000} {@content}
}
@mixin mq_1024 {
  @media #{$mq_1024} {@content}
}
@mixin mq_1200 {
  @media #{$mq_1200} {@content}
}
@mixin mq_1300 {
  @media #{$mq_1300} {@content}
}
@mixin mq_1400 {
  @media #{$mq_1400} {@content}
}
@mixin mq_1500 {
  @media #{$mq_1500} {@content}
}

/* Up - mobile fist approach */
/*
$sm-up: "#{$screen} and (min-width: #{$sm-breakpoint + 1})";  
$md-up: "#{$screen} and (min-width: #{$md-breakpoint + 1})";  
$lg-up: "#{$screen} and (min-width: #{$lg-breakpoint + 1})";  
$xlg-up: "#{$screen} and (min-width: #{$xlg-breakpoint + 1})"; 

@mixin sm-up {
  @media #{$sm-up} {@content}
}
@mixin md-up {
  @media #{$md-up} {@content}
}
@mixin lg-up {
  @media #{$lg-up} {@content}
}
@mixin xlg-up {
  @media #{$xlg-up} {@content}
}
*/

```