feat(res-to-affine): #488 partial-port slice 2 — pipe desugaring + if/else + blocks (Refs #488) (#495)

#488 partial-port slice 2: --partial now desugars ReScript pipe-first `->` (a->f(b) => f(a, b), chained left-to-right), and translates if/else and blocks with let statements. walker gains translate_pipe / translate_if / translate_as_block / translate_block(_inner) / translate_block_let; partial_function unwraps block bodies. Array/record/object literals still become () /* TODO */ holes. Parses (no parse error); 30 walker tests. Refs #488.

Author: hyperpolymath

CHANGELOG.md

@@ -20,6 +20,7 @@ this project aims to follow [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- feat(res-to-affine): partial-port mode #488 slice 2 — `--partial` now desugars ReScript pipe-first `->` (`a->f(b)` → `f(a, b)`, chained left-to-right), and translates `if`/`else` and blocks with `let` statements (Refs #488)
 - feat(res-to-affine): partial-port mode (#488) — new `--partial` flag renders module-top-level functions as AffineScript `fn` skeletons with `switch`→`match` and best-effort expression translation (literals / idents / calls / binary ops with float-op + identity-equality normalisation / `++` / member + qualified access / ternary / variant + tuple + literal patterns); un-translatable forms become `() /* TODO */` / `_ /* TODO */` holes. Output deliberately does NOT type-check but parses (verified). Distinct model from `--translate` (Refs #488)
 - feat(res-to-affine): Phase 3 slice 3 — `--translate` now also lowers module-level `let <id> = <literal>` (int/float/string/bool) to a typed `const name: T = value;`; call / `ref(...)` / destructuring bindings are skipped (not compile-time constants); every emitted form verified compilable via `main.exe check`. `switch`→`match` and qualified-path resolution remain out of the standalone-type-check scope (Refs #57)
 - feat(res-to-affine): Phase 3 slice 2 — `--translate` now also handles record types (→ `struct`) and generics (type params `'a` → `[A]`) across aliases / sums / records; `mutable`/optional-`?` records, qualified paths, and nested generics are still skipped (never guessed); every emitted form verified compilable via `main.exe check` (Refs #57)

tools/res-to-affine/README.md

@@ -222,16 +222,22 @@ AffineScript `fn` skeleton:
 | `let area = (w, h) => w *. h` | `fn area(w: _, h: _) -> _ { w * h }` |
 | `let classify = x => switch x { \| Some(n) => n + 1 \| None => 0 }` | `fn classify(x: _) -> _ { match x { Some(n) => n + 1, None => 0, } }` |
 | `let greet = name => "hi " ++ name` | `fn greet(name: _) -> _ { "hi " ++ name }` |
+| `let piped = x => x->doStuff(1)` | `fn piped(x: _) -> _ { doStuff(x, 1) }` |
+| `let chain = x => x->f->g(2)` | `fn chain(x: _) -> _ { g(f(x), 2) }` |
+| `let clamp = x => if x > 0 { x } else { 0 }` | `fn clamp(x: _) -> _ { if x > 0 { x } else { 0 } }` |
+| `let scaled = x => { let y = x + 1; y * 2 }` | `fn scaled(x: _) -> _ { let y = x + 1; y * 2 }` |
 
 It translates literals, identifiers, calls, binary operators (normalising
 ReScript's float ops `+.`/`*.` → `+`/`*` and `===`/`!==` → `==`/`!=`), string
-concat `++`, member/qualified access, ternaries, and `switch`→`match` with
-variant/tuple/literal patterns. Anything else (pipe-first `->`, records, etc.)
-becomes a `() /* TODO */` hole. The output is a partial port to finish by
-hand: it **parses** but is not expected to type-check (verified — the
-generated skeletons reach resolution/type-checking without a parse error).
-First slice; the next steps (pipe desugaring `a->f(b)` → `f(a, b)`, `if`/block
-bodies, combining with `--translate`) continue under #488.
+concat `++`, member/qualified access, ternaries, **`if`/`else`**, **blocks
+with `let` statements**, **pipe-first `->`** (`a->f(b)` → `f(a, b)`, chained
+left-to-right), and `switch`→`match` with variant/tuple/literal patterns.
+Anything else (records, arrays, objects, …) becomes a `() /* TODO */` hole.
+The output is a partial port to finish by hand: it **parses** but is not
+expected to type-check (verified — the generated skeletons reach
+resolution/type-checking without a parse error). Continuing under #488:
+record/array/object literals, labelled args, combining `--partial` with
+`--translate`, and module-qualified-reference *resolution*.
 
 ## Corpus run
 

tools/res-to-affine/test/fixtures/partial1.res

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: MIT
 // #488 partial-port fixture: module-top-level functions -> `fn` skeletons
-// with switch->match and best-effort expression translation. Output is NOT
-// expected to type-check; it must parse, with un-translatable forms as
-// `() /* TODO */` holes.
+// with switch->match, pipe desugaring, if/else, blocks, and best-effort
+// expression translation. Output is NOT expected to type-check; it must
+// parse, with un-translatable forms (e.g. an array literal) as TODO holes.
 
 let classify = x => switch x {
 | Some(n) => n + 1
@@ -15,5 +15,17 @@ let greet = name => "hi " ++ name
 
 let log2 = msg => Js.log(msg)
 
-// pipe-first has no AffineScript equivalent -> must become a TODO hole.
+// pipe-first desugars: x->doStuff(1)  ->  doStuff(x, 1)
 let piped = x => x->doStuff(1)
+
+// pipe chain desugars left-to-right: x->f->g(2)  ->  g(f(x), 2)
+let chain = x => x->f->g(2)
+
+// if/else
+let clamp = x => if x > 0 { x } else { 0 }
+
+// block with a let statement
+let scaled = x => { let y = x + 1; y * 2 }
+
+// array literal has no handler yet -> must become a TODO hole.
+let pair = x => [x, x]

tools/res-to-affine/test/test_walker.ml

@@ -401,8 +401,26 @@ let partial1_blob () =
 let test_partial_count () =
   skip_unless_ready ();
   Alcotest.(check int)
-    "five module-top-level functions -> fn skeletons"
-    5 (List.length (translate_partial1 ()))
+    "nine module-top-level functions -> fn skeletons"
+    9 (List.length (translate_partial1 ()))
+
+let test_partial_pipe () =
+  skip_unless_ready ();
+  let blob = partial1_blob () in
+  (* x->doStuff(1) -> doStuff(x, 1); chain x->f->g(2) -> g(f(x), 2) *)
+  Alcotest.(check bool) "pipe-first desugars, including left-nested chains"
+    true (contains blob "doStuff(x, 1)" && contains blob "g(f(x), 2)")
+
+let test_partial_if () =
+  skip_unless_ready ();
+  Alcotest.(check bool) "if/else translated"
+    true (contains (partial1_blob ()) "if x > 0 { x } else { 0 }")
+
+let test_partial_block () =
+  skip_unless_ready ();
+  let blob = partial1_blob () in
+  Alcotest.(check bool) "block body with a let statement translated"
+    true (contains blob "let y = x + 1" && contains blob "y * 2")
 
 let test_partial_switch_to_match () =
   skip_unless_ready ();
@@ -503,7 +521,7 @@ let () =
         ] );
       ( "walker-488-partial",
         [
-          Alcotest.test_case "five functions -> fn skeletons"
+          Alcotest.test_case "nine functions -> fn skeletons"
             `Quick test_partial_count;
           Alcotest.test_case "switch -> match + patterns + arm bodies"
             `Quick test_partial_switch_to_match;
@@ -513,5 +531,11 @@ let () =
             `Quick test_partial_concat_and_call;
           Alcotest.test_case "untranslatable form -> TODO hole"
             `Quick test_partial_todo_hole;
+          Alcotest.test_case "pipe-first desugars (incl. chains)"
+            `Quick test_partial_pipe;
+          Alcotest.test_case "if/else translated"
+            `Quick test_partial_if;
+          Alcotest.test_case "block with let statement translated"
+            `Quick test_partial_block;
         ] );
     ]

tools/res-to-affine/walker.ml

@@ -994,13 +994,14 @@ let rec translate_expr ~source n =
       match List.filter (fun c -> c.ntype <> "comment") n.children with
       | [ inner ] -> Printf.sprintf "(%s)" (translate_expr ~source inner)
       | _ -> todo_expr ~source n)
-  | "sequence_expression" | "block" -> (
+  | "pipe_expression" -> translate_pipe ~source n
+  | "if_expression" -> translate_if ~source n
+  | "block" -> translate_block ~source n
+  | "sequence_expression" -> (
       match List.filter (fun c -> c.ntype <> "comment") n.children with
       | [] -> "()"
       | [ single ] -> translate_expr ~source single
-      | many ->
-          Printf.sprintf "{ %s }"
-            (String.concat "; " (List.map (translate_expr ~source) many)))
+      | _ -> translate_block ~source n)
   | "ternary_expression" -> (
       match
         ( child_with_field "condition" n,
@@ -1089,6 +1090,91 @@ and translate_switch ~source sw =
   in
   Printf.sprintf "match %s {\n%s\n}" scrutinee (String.concat "\n" arms)
 
+(* ReScript pipe-first: `a -> f(b)` desugars to `f(a, b)`, `a -> f` to `f(a)`.
+   Pipes are left-nested so chains fall out of the recursion on [left]. *)
+and translate_pipe ~source n =
+  match List.filter (fun c -> c.ntype <> "comment") n.children with
+  | [ left; right ] -> (
+      let lhs = translate_expr ~source left in
+      match right.ntype with
+      | "call_expression" ->
+          let fn =
+            match child_with_field "function" right with
+            | Some f -> translate_expr ~source f
+            | None -> "todo_fn"
+          in
+          let rest =
+            match child_with_field "arguments" right with
+            | None -> []
+            | Some a ->
+                List.filter_map
+                  (fun c ->
+                    match c.ntype with
+                    | "type_annotation" -> None
+                    | "labeled_argument" ->
+                        Some (translate_labeled_arg ~source c)
+                    | _ -> Some (translate_expr ~source c))
+                  a.children
+          in
+          Printf.sprintf "%s(%s)" fn (String.concat ", " (lhs :: rest))
+      | _ -> Printf.sprintf "%s(%s)" (translate_expr ~source right) lhs)
+  | _ -> todo_expr ~source n
+
+and translate_if ~source n =
+  (* positional children: condition, then-block, optional else_clause. *)
+  match List.filter (fun c -> c.ntype <> "comment") n.children with
+  | cond :: then_blk :: rest ->
+      let else_part =
+        match rest with
+        | ec :: _ when ec.ntype = "else_clause" -> (
+            match List.filter (fun c -> c.ntype <> "comment") ec.children with
+            | [ b ] -> " else " ^ translate_as_block ~source b
+            | _ -> "")
+        | _ -> ""
+      in
+      Printf.sprintf "if %s %s%s" (translate_expr ~source cond)
+        (translate_as_block ~source then_blk) else_part
+  | _ -> todo_expr ~source n
+
+(* Render a node as an AffineScript braced block (if/else branches require it). *)
+and translate_as_block ~source n =
+  match n.ntype with
+  | "block" -> translate_block ~source n
+  | "if_expression" -> translate_if ~source n (* else-if chain *)
+  | _ -> Printf.sprintf "{ %s }" (translate_expr ~source n)
+
+and translate_block ~source n =
+  Printf.sprintf "{ %s }" (translate_block_inner ~source n)
+
+(* The statements of a block, `;`-joined, WITHOUT the surrounding braces (so a
+   function body can place them directly inside the `fn { … }`). *)
+and translate_block_inner ~source n =
+  String.concat "; "
+    (List.filter_map
+       (fun c ->
+         match c.ntype with
+         | "comment" -> None
+         | "let_declaration" -> Some (translate_block_let ~source c)
+         | _ -> Some (translate_expr ~source c))
+       n.children)
+
+and translate_block_let ~source ld =
+  let one lb =
+    let name =
+      match child_with_field "pattern" lb with
+      | Some p -> translate_pattern ~source p
+      | None -> "_"
+    in
+    let v =
+      match child_with_field "body" lb with
+      | Some b -> translate_expr ~source b
+      | None -> "()"
+    in
+    Printf.sprintf "let %s = %s" name v
+  in
+  String.concat "; "
+    (List.map one (List.filter (fun c -> c.ntype = "let_binding") ld.children))
+
 let translate_param ~source p =
   match p.ntype with
   | "value_identifier" -> node_text ~source p ^ ": _"
@@ -1119,6 +1205,8 @@ let partial_function ~source ~name fn =
   in
   let body =
     match child_with_field "body" fn with
+    (* a block body's statements go directly inside the fn braces (no nesting) *)
+    | Some b when b.ntype = "block" -> translate_block_inner ~source b
     | Some b -> translate_expr ~source b
     | None -> "()"
   in