Source file type_expr.ml

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     This file is part of Merlin, an helper for ocaml editors

     Copyright (C) 2013 - 2024  Xavier Van de Woestyne <xaviervdw(_)gmail.com>
                                Arthur Wendling <arthur(_)tarides.com>


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type t =
  | Arrow of t * t
  | Tycon of string * t list
  | Tuple of t list
  | Tyvar of int
  | Wildcard
  | Unhandled

let rec equal a b =
  match (a, b) with
  | Unhandled, Unhandled | Wildcard, Wildcard -> true
  | Tyvar a, Tyvar b -> Int.equal a b
  | Tuple a, Tuple b -> List.equal equal a b
  | Tycon (ka, a), Tycon (kb, b) -> String.equal ka kb && List.equal equal a b
  | Arrow (ia, oa), Arrow (ib, ob) -> equal ia ib && equal oa ob
  | Arrow (_, _), _
  | Tycon (_, _), _
  | Tuple _, _
  | Tyvar _, _
  | Wildcard, _
  | Unhandled, _ -> false

let parens x = "(" ^ x ^ ")"

let tyvar_to_string x =
  let rec aux acc i =
    let c = Char.code 'a' + (i mod 26) |> Char.chr in
    let acc = acc ^ String.make 1 c in
    if i < 26 then acc else aux acc (i - 26)
  in
  aux "'" x

let unhandled = "?"

let rec to_string = function
  | Unhandled -> unhandled
  | Wildcard -> "_"
  | Tyvar i -> tyvar_to_string i
  | Tycon (constr, []) -> constr
  | Tycon (constr, [ x ]) -> with_parens x ^ " " ^ constr
  | Tycon (constr, xs) -> (xs |> as_list "" |> parens) ^ " " ^ constr
  | Tuple xs -> as_tuple "" xs
  | Arrow (a, b) -> with_parens a ^ " -> " ^ to_string b

and with_parens = function
  | (Arrow _ | Tuple _) as t -> t |> to_string |> parens
  | t -> to_string t

and as_list acc = function
  | [] -> acc ^ unhandled
  | [ x ] -> acc ^ to_string x
  | x :: xs ->
    let acc = acc ^ to_string x ^ ", " in
    as_list acc xs

and as_tuple acc = function
  | [] -> acc ^ unhandled
  | [ x ] -> acc ^ with_parens x
  | x :: xs ->
    let acc = acc ^ with_parens x ^ " * " in
    as_tuple acc xs

module SMap = Map.Make (String)

let map_with_state f i map list =
  let i, map, r =
    list
    |> List.fold_left
         (fun (i, map, acc) x ->
           let i, map, elt = f i map x in
           (i, map, elt :: acc))
         (i, map, [])
  in
  (i, map, List.rev r)

let normalize_type_parameters ty =
  let rec aux i map = function
    | Type_parsed.Unhandled -> (i, map, Unhandled)
    | Type_parsed.Wildcard -> (i, map, Wildcard)
    | Type_parsed.Arrow (a, b) ->
      let i, map, a = aux i map a in
      let i, map, b = aux i map b in
      (i, map, Arrow (a, b))
    | Type_parsed.Tycon (s, r) ->
      let i, map, r = map_with_state aux i map r in
      (i, map, Tycon (s, r))
    | Type_parsed.Tuple r ->
      let i, map, r = map_with_state aux i map r in
      (i, map, Tuple r)
    | Type_parsed.Tyvar var ->
      let i, map, value =
        match SMap.find_opt var map with
        | Some value -> (i, map, value)
        | None ->
          let i = succ i in
          let map = SMap.add var i map in
          (i, map, i)
      in
      (i, map, Tyvar value)
  in
  let _, _, normalized = aux ~-1 SMap.empty ty in
  normalized

let from_string str =
  try
    str |> Lexing.from_string
    |> Type_parser.main Type_lexer.token
    |> normalize_type_parameters |> Option.some
  with _ -> None