Fixed version for materialdesignicons with scssphp

_functions.scss

@function char($character-code) {
    @if function-exists("selector-append") {
        @return unquote("\"\\#{$character-code}\"");
    }

    @if "\\#{'x'}" == "\\x" {
        @return str-slice("\x", 1, 1) + $character-code;
    }
    @else {
        @return str-slice("\x",1,1) + $character-code;
    }
}

@function mdi($name) {
    @if map-has-key($mdi-icons, $name) == false {
        @warn "Icon #{$name} not found.";
        @return "";
    }
    @return char(map-get($mdi-icons, $name));
}