Type record projections and collection operators

src/infer.ml

@@ -227,6 +227,13 @@ let rec infer env syntax =
       Typed.make (Typed.TBinop (Syntax.Sub, Typed.make (Typed.TInt 0) Types.TInt span, operand)) Types.TInt span
   | Resolve.RTuple items ->
       let items = List.map (infer env) items in
+      List.iter
+        (fun item ->
+          if contains_collection item.Typed.ty then
+            Diagnostic.error item.Typed.tspan
+              "collections may not appear inside tuples, but this component has type %s"
+              (Types.pp item.Typed.ty))
+        items;
       Typed.make (Typed.TTuple items) (Types.TTuple (List.map (fun item -> item.Typed.ty) items)) span
   | Resolve.RRecord fields -> infer_record env span fields
   | Resolve.RField (record, label) ->
@@ -234,15 +241,32 @@ let rec infer env syntax =
       (match Util.assoc_opt label env.ctx.Types.labels with
       | None -> Diagnostic.error span "no record type declares a field named `%s`" label
       | Some (name, field_ty) ->
-          Types.unify span record.Typed.ty (Types.TRecord name);
+          (match Types.repr record.Typed.ty with
+          | Types.TRecord actual when actual = name -> ()
+          | Types.TVar _ -> Types.unify span record.Typed.ty (Types.TRecord name)
+          | other ->
+              Diagnostic.error span "cannot project field `%s` from a value of type %s" label
+                (Types.pp other));
           Typed.make (Typed.TField (record, label)) field_ty span)
 
+and infer_function env element argument =
+  match argument.Resolve.r with
+  | Resolve.RLambda (ident, body) ->
+      let body = infer (bind env ident (scheme_of element)) body in
+      Typed.make (Typed.TLambda (ident, body)) (Types.TArrow (element, body.Typed.ty))
+        argument.Resolve.rspan
+  | _ ->
+      let fn = infer env argument in
+      let result = Types.fresh_var () in
+      Types.unify argument.Resolve.rspan fn.Typed.ty (Types.TArrow (element, result));
+      fn
+
 and infer_filter env span predicate collection =
   let collection = infer env collection in
   let element = Types.fresh_var () in
   Types.unify collection.Typed.tspan collection.Typed.ty (Types.TCollection element);
   check_element collection.Typed.tspan "filter element" element;
-  let predicate = infer env predicate in
+  let predicate = infer_function env element predicate in
   Types.unify predicate.Typed.tspan predicate.Typed.ty (Types.TArrow (element, Types.TBool));
   Typed.make (Typed.TFilter (collection, predicate)) collection.Typed.ty span
 
@@ -251,7 +275,7 @@ and infer_map env span projection collection =
   let element = Types.fresh_var () in
   Types.unify collection.Typed.tspan collection.Typed.ty (Types.TCollection element);
   check_element collection.Typed.tspan "map element" element;
-  let projection = infer env projection in
+  let projection = infer_function env element projection in
   let result = Types.fresh_var () in
   Types.unify projection.Typed.tspan projection.Typed.ty (Types.TArrow (element, result));
   check_element projection.Typed.tspan "mapped element" result;