Special functions in Sass

spfun.sass

$roboto-font-path: "../fonts/roboto"

@font-face
    // This is parsed as a normal function call that takes a quoted string.
    src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2")

    font-family: "Roboto"
    font-weight: 100


@font-face
    // This is parsed as a normal function call that takes an arithmetic
    // expression.
    src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2")

    font-family: "Roboto"
    font-weight: 300


@font-face
    // This is parsed as an interpolated special function.
    src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2")

    font-family: "Roboto"
    font-weight: 400