fmt_test.ml

type bin_op = Plus | Minus

type value = Int of int
           | Unit

type exp =
  | Val of value
  | Out of value
  | BinOp of bin_op*value*value


let value_fmt : value Fmt.t = fun pp v ->
  match v with
  | Int i -> Fmt.int pp i
  | Unit -> Fmt.string pp "()"

let bin_op_fmt : bin_op Fmt.t = fun pp op ->
  match op with
  | Plus -> Fmt.char pp '+'
  | Minus -> Fmt.char pp '-'

let exp_fmt : exp Fmt.t = fun pp e ->
  match e with
  | Val v -> value_fmt pp v
  | Out v ->
     let f = Fmt.(prefix (const string "out") (parens value_fmt)) in
     f pp v
  | BinOp (op, v1, v2) ->
     let f = Fmt.(pair value_fmt (pair bin_op_fmt value_fmt)) in
     f pp (v1, (op, v2))

let test = BinOp (Plus, Int 1, Int 10)
let () =
  Fmt.pr "%a" (Fmt.hbox exp_fmt) test

(* ocamlfind ocamlc -package fmt -linkpkg fmt_test.ml   *)