// Slices $list between $start and $end
// -------------------------------------------------------------------------------
// @documentation http://sassylists.com/documentation/#slice
// -------------------------------------------------------------------------------
// @example slice(a b c d,  2, 3) => b, c
// @example slice(a b c d,  3, 2) => error
// @example slice(a b c d,  3, 5) => error
// @example slice(a b c d, -1, 3) => error
// @example slice(a b c d,  0, 3) => error
// @example slice(a b c d,  3, 3) => c
// -------------------------------------------------------------------------------
// @param $list [List] : list
// @param $start [Number] : start index
// @param $end [Number] : end index
// -------------------------------------------------------------------------------
// @raise [Error] if $start or $end aren't integers
// @raise [Error] if $start is greater than $end
// @raise [Error] if $start or $end is strictly lesser than 1
// @raise [Error] if $start is strictly greater than length of $list
// @raise [Error] if $end is strictly greater than length of $list
// -------------------------------------------------------------------------------
// @return [List] | false

@function slice($list, $start: 1, $end: length($list)) {
    $result: false;

    @if type-of($start) != number or type-of($end) != number {
        @warn "List indexes #{$start} and #{$end} must be numbers for `slice`.";
        @return $result;
    }

    @else if $start > $end {
        @warn "Start index is #{$start} but has to be lesser than or equals to the end index (#{$end}) for `slice`.";
        @return $result;
    }

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

    @else if $start > length($list) {
        @warn "Start index is #{$start} but list is only #{length($list)} items long for `slice`.";
        @return $result;
    }

    @else if $end > length($list) {
        @warn "End index is #{$end} but list is only #{length($list)} items long for `slice`.";
        @return $result;
    }

    @else {
        $result: ();
            
        @for $i from $start through $end {
            $result: append($result, nth($list, $i));
        }
    }

    @return $result;
}