Desugar: Do not stumble over a function of type Non

src/construct.ml

@@ -509,3 +509,7 @@ let forE pat exp1 exp2 =
       )
     )
   )
+
+let unreachableE =
+  (* Do we want UnreachableE in the AST *)
+  loopE unitE

src/construct.mli

@@ -73,6 +73,8 @@ val declare_idE : id -> typ -> exp -> exp
 val define_idE : id -> mut -> exp -> exp
 val newObjE : obj_sort -> Ir.field list -> typ -> exp
 
+val unreachableE : exp
+
 (* Declarations *)
 
 val letP : pat -> exp -> dec

src/desugar.ml

@@ -72,9 +72,13 @@ and exp' at note = function
     let args, wrap = to_args cc p in
     I.FuncE (name, cc, typ_binds tbs, args, Type.as_seq ty.note, wrap (exp e))
   | S.CallE (e1, inst, e2) ->
-    let cc = Value.call_conv_of_typ e1.Source.note.S.note_typ in
-    let inst = List.map (fun t -> t.Source.note) inst in
-    I.CallE (cc, exp e1, inst, exp e2)
+    let t = e1.Source.note.S.note_typ in
+    if Type.is_non t
+    then unreachableE.it
+    else
+      let cc = Value.call_conv_of_typ t in
+      let inst = List.map (fun t -> t.Source.note) inst in
+      I.CallE (cc, exp e1, inst, exp e2)
   | S.BlockE [] -> I.TupE []
   | S.BlockE [{it = S.ExpD e; _}] -> (exp e).it
   | S.BlockE ds -> I.BlockE (block (Type.is_unit note.S.note_typ) ds)

src/type.ml

@@ -294,6 +294,7 @@ let rec promote = function
 
 (* Projections *)
 
+let is_non = function Non -> true | _ -> false
 let is_prim p = function Prim p' -> p = p' | _ -> false
 let is_obj = function Obj _ -> true | _ -> false
 let is_variant = function Variant _ -> true | _ -> false

src/type.mli

@@ -65,6 +65,7 @@ val prim : string -> prim
 
 (* Projection *)
 
+val is_non : typ -> bool
 val is_prim : prim -> typ -> bool
 val is_obj : typ -> bool
 val is_variant : typ -> bool