Extraction: avoid using ignore around a unit expression

src/mlw/compile.ml

@@ -266,7 +266,7 @@ module Translate = struct
     | Elet (LDvar (pv, e1), e2)
       when pv.pv_ghost || not (Mpv.mem pv e2.e_effect.eff_reads) ->
         if eff_pure e1.e_effect then expr info svar mask e2
-        else let e1 = ML.e_ignore (expr info svar MaskGhost e1) in
+        else let e1 = ML.e_ignore e1.e_ity (expr info svar MaskGhost e1) in
           ML.e_seq e1 (expr info svar mask e2) (ML.I e.e_ity) mask eff lbl
     | Elet (LDvar (pv, e1), e2) ->
         Debug.dprintf debug_compile "compiling local definition of %s@."

src/mlw/mltree.ml

@@ -308,11 +308,10 @@ let e_app rs pvl =
 
 let e_fun args e = mk_expr (Efun (args, e))
 
-let e_ignore e =
+let e_ignore e_ity e =
   (* TODO : avoid ignore around a unit type expresson *)
-  (* if is_unit e.e_ity then begin Format.eprintf "hit!@."; e end
-   * else *)
-  mk_expr (Eignore e) ity_unit MaskVisible e.e_effect e.e_label
+  if ity_equal e_ity Ity.ity_unit then e
+  else mk_expr (Eignore e) ity_unit MaskVisible e.e_effect e.e_label
 
 let e_if e1 e2 e3 =
   mk_expr (Eif (e1, e2, e3)) e2.e_ity