sass using variable as mixin data

Question

I'm using grid from csswizardry and wanting to create breakpoints as variables... If defined as standard "strings":

$breakpoints: (
    'palm' '(max-width: 480px)'
)!default;

But when I change it to:

$palmmaxwidth: 480px;
$breakpoints: (
    'palm' '(max-width: $palmmaxwidth)'
)!default;

it will not compile correctly within the mixin:

@mixin grid-media-query($media-query){
    $breakpoint-found: false;

    @each $breakpoint in $breakpoints{
        $name: nth($breakpoint, 1);
        $declaration: nth($breakpoint, 2);

        @if $media-query == $name and $declaration{
            $breakpoint-found: true;

            @media only screen and #{$declaration}{
                @content;
            }
        }
    }

    @if $breakpoint-found == false{
        @warn "Breakpoint ‘#{$media-query}’ does not exist"
    }
}

The error is Invalid CSS after "...nd (max-width: ": expected expression (e.g. 1px, bold), was "$palmmaxwidth)"

What am I missing?

Answer 1

The solution is quite simple after trying every possible combination:

$breakpoints: (
    'palm' '(max-width: '+$palmmaxwidth+')'
)!default;