I grabbed the code from the article and annotated it with the different cases from the famous picture* switch (expr.kind) { case "number"/"string"/"var":

I grabbed the code from the article and annotated it with the different cases from the famous picture* switch (expr.kind) { case "number"/"string"/"var": ... [Var] case "call": ... [App] case "function": throw new Error("...[Abs]") case "let": ... [Let] Looks like most of the hard work's done, and probably wouldn't be too tricky to get [Abs] in there too! * https://wikimedia.org/api/rest_v1/media/math/render/svg/10d6e781d61259108db5fbfcfd84cb47daac33a6 https://wikimedia.org/api/rest_v1/media/math/render/svg/10d6...