Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

// Our project defines some themes
$themes: (
  foo: (
    foreground: #5b5b5b,
    background: #f3f3f3
  )
);

// Our library also defines some themes
$libraryThemes: (
  foo: (
    foreground: #ccc,
    background: #3b3b3b
  ),
  bar: (
    foreground: #ccc,
    background: #3b3b3b
  ),
);

// Our library checks to see if there any priority themes to use
@if (variable-exists(themes)) {
  // if some exist, merge with the library giving the project themes priority
  $themes: map-merge($libraryThemes, $themes);
} @else {
  // if there aren't, just use the library themes
  $themes: $libraryThemes;
}

@function get-theme($name) {
  @return map-get($themes, $name);
}

@function add-theme($theme, $name) {
  @return map-merge($themes, ( $name : $theme));
}

@function requires($theme, $props) {
  @each $key in $props {
    @if (not map-has-key($theme, $key)) {
      @warn "To use this theme requires #{$key} to be set in the map";
      @return false;
    } 
  }

  @return true;
}

.debug{
  themes: inspect($themes);
  valid: requires(get-theme(foo), foreground background);
  valid: requires(get-theme(foo), foreground background border);
}

@if (requires(get-theme(foo), foreground background)) {
  /* Include mixin here, we know that all requirements are satisfied */
} @else {
  /* Don't include mixin as we know that a required property is missing */
}

@if (requires(get-theme(foo), foreground background border)) {
  /* Include mixin here, we know that all requirements are satisfied */
} @else {
  /* Don't include mixin as we know that a required property is missing */
}

$themes: add-theme((
  foreground: blue,
  background: white
), baz);

/*
Now our $themes looks like this:
#{inspect($themes)}
*/

SassMeister-output.css

.debug {
  themes: (foo: (foreground: #5b5b5b, background: #f3f3f3), bar: (foreground: #ccc, background: #3b3b3b));
  valid: true;
  valid: false;
}

/* Include mixin here, we know that all requirements are satisfied */
/* Don't include mixin as we know that a required property is missing */
/*
Now our $themes looks like this:
(foo: (foreground: #5b5b5b, background: #f3f3f3), bar: (foreground: #ccc, background: #3b3b3b), baz: (foreground: blue, background: white))
*/