refactor(wpcarro/compiler): Modularize debug fns

Define `debug.ml` and `prettify.ml` to clean-up some code.

Change-Id: Iee2e1ed666f2ccb5e56cc50054ca85b8ba513f3b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7078
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>

users/wpcarro/scratch/compiler/debug.ml

@@ -0,0 +1,66 @@
+open Types
+
+(* Print x prefixed with tag and return x unchanged. *)
+let print (f : 'a -> string) (tag : string) (x : 'a) : 'a =
+  Printf.printf "%s: %s\n" tag (f x);
+  x
+
+let rec ast (tree : Types.value) : string =
+  match tree with
+  | ValueLiteral (LiteralBool x) ->
+     Printf.sprintf "ValueLiteral (LiteralBool %s)" (string_of_bool x)
+  | ValueLiteral (LiteralInt x) ->
+     Printf.sprintf "ValueLiteral (LiteralInt %s)" (string_of_int x)
+  | ValueVariable x ->
+     Printf.sprintf "ValueVariable %s" x
+  | ValueFunction (x, body) ->
+     Printf.sprintf "ValueFunction (%s, %s)" x (ast body)
+  | ValueApplication (f, x) ->
+     Printf.sprintf "ValueApplication (%s, %s)" (ast f) (ast x)
+  | ValueVarApplication (f, x) ->
+     Printf.sprintf "ValueVarApplication (%s, %s)" f (ast x)
+  | ValueBinder (k, v, x) ->
+      Printf.sprintf "ValueBinder (%s, %s, %s)" k (ast v) (ast x)
+
+let rec value (x : value) : string =
+  match x with
+  | ValueLiteral (LiteralInt x) ->
+     Printf.sprintf "Int %d" x
+  | ValueLiteral (LiteralBool x) ->
+     Printf.sprintf "Bool %b" x
+  | ValueVariable x ->
+     Printf.sprintf "Var %s" x
+  | ValueFunction (name, x) ->
+     Printf.sprintf "Fn %s %s" name (value x)
+  | ValueApplication (f, x) ->
+     Printf.sprintf "App %s %s" (value f) (value x)
+  | ValueVarApplication (name, x) ->
+     Printf.sprintf "App %s %s" name (value x)
+  | ValueBinder (name, x, body) ->
+     Printf.sprintf "Bind %s %s %s" name (value x) (value body)
+
+let rec type' (t : _type) : string =
+  match t with
+  | TypeInt -> "Integer"
+  | TypeBool -> "Boolean"
+  | TypeVariable k -> Printf.sprintf "%s" k
+  | TypeArrow (a, b) -> Printf.sprintf "%s -> %s" (type' a) (type' b)
+
+let quantified_type (q : quantified_type) : string =
+  let QuantifiedType (vars, t) = q in
+  if List.length vars == 0 then
+    Printf.sprintf "%s" (type' t)
+  else
+    Printf.sprintf "forall %s. %s" (String.concat "," vars) (type' t)
+
+let substitution (s : substitution) : string =
+  FromString.fold (fun k v acc -> Printf.sprintf "%s\"%s\" |-> %s;" acc k (type' v)) s ""
+  |> Printf.sprintf "{ %s }"
+
+let env (s : env) : string =
+  FromString.fold (fun k v acc -> Printf.sprintf "%s\"%s\" |-> %s;" acc k (quantified_type v)) s ""
+  |> Printf.sprintf "{ %s }"
+
+let inference (Inference (s, t)) =
+  Printf.sprintf "type: %s; sub: %s" (type' t) (substitution s)
+