diff --git a/src/main/run_source.ml b/src/main/run_source.ml
index 1c452c91d..26a3cd87e 100644
--- a/src/main/run_source.ml
+++ b/src/main/run_source.ml
@@ -51,7 +51,7 @@ let transpile_value
   let%bind f =
     let open Transpiler in
     let (f , _) = functionalize e in
-    let%bind main = translate_main f in
+    let%bind main = translate_main f e.location in
     ok main
   in
 
diff --git a/src/main/run_typed.ml b/src/main/run_typed.ml
index a7f9fdc58..47a67469d 100644
--- a/src/main/run_typed.ml
+++ b/src/main/run_typed.ml
@@ -5,7 +5,7 @@ let transpile_value
   let%bind f =
     let open Transpiler in
     let (f , _) = functionalize e in
-    let%bind main = translate_main f in
+    let%bind main = translate_main f e.location in
     ok main
   in
 
diff --git a/src/simplify/ligodity.ml b/src/simplify/ligodity.ml
index 640a1cfb8..b217325ce 100644
--- a/src/simplify/ligodity.ml
+++ b/src/simplify/ligodity.ml
@@ -79,7 +79,7 @@ let rec simpl_type_expression : Raw.type_expr -> type_expression result = fun te
       in
       ok @@ T_function (a , b)
     )
-  | TApp x ->
+  | TApp x -> (
       let (name, tuple) = x.value in
       let lst = npseq_to_list tuple.value.inside in
       let%bind cst =
@@ -88,10 +88,11 @@ let rec simpl_type_expression : Raw.type_expr -> type_expression result = fun te
       in
       let%bind lst' = bind_map_list simpl_type_expression lst in
       ok @@ T_constant (cst , lst')
-  | TProd p ->
-      let%bind tpl = simpl_list_type_expression
-        @@ npseq_to_list p.value in
+    )
+  | TProd p -> (
+      let%bind tpl = simpl_list_type_expression  @@ npseq_to_list p.value in
       ok tpl
+    )
   | TRecord r ->
       let aux = fun (x, y) -> let%bind y = simpl_type_expression y in ok (x, y) in
       let%bind lst =
diff --git a/src/transpiler/transpiler.ml b/src/transpiler/transpiler.ml
index a146358fa..7523e08dd 100644
--- a/src/transpiler/transpiler.ml
+++ b/src/transpiler/transpiler.ml
@@ -15,7 +15,78 @@ let map_of_kv_list lst =
   let open AST.SMap in
   List.fold_left (fun prev (k, v) -> add k v prev) empty lst
 
+module Errors = struct
+  let corner_case ~loc message =
+    let title () = "corner case" in
+    let content () = "we don't have a good error message for this case. we are
+striving find ways to better report them and find the use-cases that generate
+them. please report this to the developers." in
+    let data = [
+      ("location" , fun () -> loc) ;
+      ("message" , fun () -> message) ;
+    ] in
+    error ~data title content
+
+  let unrecognized_type_constant name =
+    let title () = "unrecognized type constant" in
+    let content () = name in
+    error title content
+
+  let unsupported_pattern_matching kind location =
+    let title () = "unsupported pattern-matching" in
+    let content () = Format.asprintf "%s patterns aren't supported yet" kind in
+    let data = [
+      ("location" , fun () -> Format.asprintf "%a" Location.pp location) ;
+    ] in
+    error ~data title content
+
+  let not_functional_main location =
+    let title () = "not functional main" in
+    let content () = "main should be a function" in
+    let data = [
+      ("location" , fun () -> Format.asprintf "%a" Location.pp location) ;
+    ] in
+    error ~data title content
+
+  let missing_entry_point name =
+    let title () = "missing entry point" in
+    let content () = "no entry point with the given name" in
+    let data = [
+      ("name" , fun () -> name) ;
+    ] in
+    error ~data title content
+
+  let wrong_mini_c_value expected_type actual =
+    let title () = "illed typed intermediary value" in
+    let content () = "type of intermediary value doesn't match what was expected" in
+    let data = [
+      ("expected_type" , fun () -> expected_type) ;
+      ("actual" , fun () -> Format.asprintf "%a" Mini_c.PP.value actual ) ;
+    ] in
+    error ~data title content
+
+  let bad_untranspile bad_type value =
+    let title () = "untranspiling bad value" in
+    let content () = Format.asprintf "can not untranspile %s" bad_type in
+    let data = [
+      ("bad_type" , fun () -> bad_type) ;
+      ("value" , fun () -> Format.asprintf "%a" Mini_c.PP.value value) ;
+    ] in
+    error ~data title content
+
+  let unknown_untranspile unknown_type value =
+    let title () = "untranspiling unknown value" in
+    let content () = Format.asprintf "can not untranspile %s" unknown_type in
+    let data = [
+      ("unknown_type" , fun () -> unknown_type) ;
+      ("value" , fun () -> Format.asprintf "%a" Mini_c.PP.value value) ;
+    ] in
+    error ~data title content
+end
+open Errors
+
 let rec translate_type (t:AST.type_value) : type_value result =
+  trace (simple_info "") @@
   match t.type_value' with
   | T_constant ("bool", []) -> ok (T_base Base_bool)
   | T_constant ("int", []) -> ok (T_base Base_int)
@@ -37,12 +108,7 @@ let rec translate_type (t:AST.type_value) : type_value result =
   | T_constant ("option", [o]) ->
       let%bind o' = translate_type o in
       ok (T_option o')
-  | T_constant (name , lst) ->
-      let error =
-        let title () = "unrecognized type constant" in
-        let content () = Format.asprintf "%s (%d)" name (List.length lst) in
-        error title content in
-      fail error
+  | T_constant (name , _lst) -> fail @@ unrecognized_type_constant name
   | T_sum m ->
       let node = Append_tree.of_list @@ list_of_map m in
       let aux a b : type_value result =
@@ -163,8 +229,12 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
   let%bind tv = translate_type ae.type_annotation in
   let return ?(tv = tv) expr = ok @@ Combinators.Expression.make_tpl (expr, tv) in
   let f = translate_annotated_expression in
+  let info =
+    let title () = "translating expression" in
+    let content () = Format.asprintf "%a" Location.pp ae.location in
+    info title content in
+  trace info @@
   match ae.expression with
-    (* Optimise immediate application as a let-in *)
   | E_let_in {binder; rhs; result} ->
     let%bind rhs' = translate_annotated_expression rhs in
     let%bind result' = translate_annotated_expression result in
@@ -185,14 +255,16 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
       let%bind a = translate_annotated_expression a in
       let%bind b = translate_annotated_expression b in
       return @@ E_application (a, b)
-  | E_constructor (m, param) ->
+  | E_constructor (m, param) -> (
       let%bind param' = translate_annotated_expression param in
       let (param'_expr , param'_tv) = Combinators.Expression.(get_content param' , get_type param') in
-      let%bind node_tv = tree_of_sum ae.type_annotation in
+      let%bind node_tv =
+        trace_strong (corner_case ~loc:__LOC__ "getting lr tree") @@
+        tree_of_sum ae.type_annotation in
       let leaf (k, tv) : (expression' option * type_value) result =
         if k = m then (
           let%bind _ =
-            trace (simple_error "constructor parameter doesn't have expected type (shouldn't happen here)")
+            trace_strong (corner_case ~loc:__LOC__ "wrong type for constructor parameter")
             @@ AST.assert_type_value_eq (tv, param.type_annotation) in
           ok (Some (param'_expr), param'_tv)
         ) else (
@@ -204,16 +276,17 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
         let%bind b = b in
         match (a, b) with
         | (None, a), (None, b) -> ok (None, T_or (a, b))
-        | (Some _, _), (Some _, _) -> simple_fail "several identical constructors in the same variant (shouldn't happen here)"
+        | (Some _, _), (Some _, _) -> fail @@ corner_case ~loc:__LOC__ "multiple identical constructors in the same variant"
         | (Some v, a), (None, b) -> ok (Some (E_constant ("LEFT", [Combinators.Expression.make_tpl (v, a)])), T_or (a, b))
         | (None, a), (Some v, b) -> ok (Some (E_constant ("RIGHT", [Combinators.Expression.make_tpl (v, b)])), T_or (a, b))
       in
       let%bind (ae_opt, tv) = Append_tree.fold_ne leaf node node_tv in
       let%bind ae =
-        trace_option (simple_error "constructor doesn't exist in claimed type (shouldn't happen here)")
+        trace_option (corner_case ~loc:__LOC__ "inexistant constructor")
           ae_opt in
       return ~tv ae
-  | E_tuple lst ->
+    )
+  | E_tuple lst -> (
       let node = Append_tree.of_list lst in
       let aux (a:expression result) (b:expression result) : expression result =
         let%bind a = a in
@@ -224,11 +297,16 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
         return ~tv @@ E_constant ("PAIR", [a; b])
       in
       Append_tree.fold_ne (translate_annotated_expression) aux node
-  | E_tuple_accessor (tpl, ind) ->
+    )
+  | E_tuple_accessor (tpl, ind) -> (
       let%bind ty' = translate_type tpl.type_annotation in
-      let%bind ty_lst = get_t_tuple tpl.type_annotation in
+      let%bind ty_lst =
+        trace_strong (corner_case ~loc:__LOC__ "not a tuple") @@
+        get_t_tuple tpl.type_annotation in
       let%bind ty'_lst = bind_map_list translate_type ty_lst in
-      let%bind path = tuple_access_to_lr ty' ty'_lst ind in
+      let%bind path =
+        trace_strong (corner_case ~loc:__LOC__ "tuple access") @@
+        tuple_access_to_lr ty' ty'_lst ind in
       let aux = fun pred (ty, lr) ->
         let c = match lr with
           | `Left -> "CAR"
@@ -237,7 +315,8 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
       let%bind tpl' = translate_annotated_expression tpl in
       let expr = List.fold_left aux tpl' path in
       ok expr
-  | E_record m ->
+    )
+  | E_record m -> (
       let node = Append_tree.of_list @@ list_of_map m in
       let aux a b : expression result =
         let%bind a = a in
@@ -247,12 +326,18 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
         let tv = T_pair (a_ty , b_ty) in
         return ~tv @@ E_constant ("PAIR", [a; b])
       in
+      trace_strong (corner_case ~loc:__LOC__ "record build") @@
       Append_tree.fold_ne (translate_annotated_expression) aux node
+    )
   | E_record_accessor (record, property) ->
       let%bind ty' = translate_type (get_type_annotation record) in
-      let%bind ty_smap = get_t_record (get_type_annotation record) in
+      let%bind ty_smap =
+        trace_strong (corner_case ~loc:__LOC__ "not a record") @@
+        get_t_record (get_type_annotation record) in
       let%bind ty'_smap = bind_map_smap translate_type ty_smap in
-      let%bind path = record_access_to_lr ty' ty'_smap property in
+      let%bind path =
+        trace_strong (corner_case ~loc:__LOC__ "record access") @@
+        record_access_to_lr ty' ty'_smap property in
       let aux = fun pred (ty, lr) ->
         let c = match lr with
           | `Left -> "CAR"
@@ -261,38 +346,49 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
       let%bind record' = translate_annotated_expression record in
       let expr = List.fold_left aux record' path in
       ok expr
-  | E_constant (name, lst) ->
-      let%bind lst' = bind_list @@ List.map (translate_annotated_expression) lst in (
-        match name, lst with
-        | "NONE", [] ->
-            let%bind o = Mini_c.Combinators.get_t_option tv in
-            return @@ E_make_none o
-        | _ -> return @@ E_constant (name, lst')
-      )
+  | E_constant (name, lst) -> (
+      let%bind lst' = bind_map_list (translate_annotated_expression) lst in
+      match name, lst with
+      | "NONE", [] ->
+        let%bind o =
+          trace_strong (corner_case ~loc:__LOC__ "not an option") @@
+          Mini_c.Combinators.get_t_option tv in
+        return @@ E_make_none o
+      | _ -> return @@ E_constant (name, lst')
+    )
   | E_lambda l ->
-    let%bind env = transpile_environment ae.environment in
+    let%bind env =
+      trace_strong (corner_case ~loc:__LOC__ "environment") @@
+      transpile_environment ae.environment in
     translate_lambda env l
-  | E_list lst ->
-      let%bind t = Mini_c.Combinators.get_t_list tv in
+  | E_list lst -> (
+      let%bind t =
+        trace_strong (corner_case ~loc:__LOC__ "not a list") @@
+        Mini_c.Combinators.get_t_list tv in
       let%bind lst' = bind_map_list (translate_annotated_expression) lst in
       let aux : expression -> expression -> expression result = fun prev cur ->
         return @@ E_constant ("CONS", [cur ; prev]) in
       let%bind (init : expression) = return @@ E_make_empty_list t in
       bind_fold_list aux init lst'
-  | E_map m ->
-      let%bind (src, dst) = Mini_c.Combinators.get_t_map tv in
+    )
+  | E_map m -> (
+      let%bind (src, dst) =
+        trace_strong (corner_case ~loc:__LOC__ "not a map") @@
+        Mini_c.Combinators.get_t_map tv in
       let aux : expression result -> (AST.ae * AST.ae) -> expression result = fun prev (k, v) ->
         let%bind prev' = prev in
         let%bind (k', v') =
           let v' = e_a_some v ae.environment in
-          bind_map_pair (translate_annotated_expression) (k, v') in
+          bind_map_pair (translate_annotated_expression) (k , v') in
         return @@ E_constant ("UPDATE", [k' ; v' ; prev'])
       in
       let init = return @@ E_make_empty_map (src, dst) in
       List.fold_left aux init m
-  | E_look_up dsi ->
+    )
+  | E_look_up dsi -> (
       let%bind (ds', i') = bind_map_pair f dsi in
       return @@ E_constant ("MAP_GET", [i' ; ds'])
+    )
   | E_sequence (a , b) -> (
       let%bind a' = translate_annotated_expression a in
       let%bind b' = translate_annotated_expression b in
@@ -309,27 +405,25 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
         fun (prev, acc) cur ->
           let%bind ty' = translate_type prev in
           match cur with
-          | Access_tuple ind ->
-              let%bind ty_lst = AST.Combinators.get_t_tuple prev in
+          | Access_tuple ind -> (
+              let%bind ty_lst =
+                trace_strong (corner_case ~loc:__LOC__ "not a tuple") @@
+                AST.Combinators.get_t_tuple prev in
               let%bind ty'_lst = bind_map_list translate_type ty_lst in
               let%bind path = tuple_access_to_lr ty' ty'_lst ind in
               let path' = List.map snd path in
               ok (List.nth ty_lst ind, acc @ path')
-          | Access_record prop ->
-              let%bind ty_map =
-                let error =
-                  let title () = "accessing property on not a record" in
-                  let content () = Format.asprintf "%s on %a in %a"
-                    prop Ast_typed.PP.type_value prev Ast_typed.PP.annotated_expression expr in
-                  error title content
-                in
-                trace error @@
+            )
+          | Access_record prop -> (
+            let%bind ty_map =
+                trace_strong (corner_case ~loc:__LOC__ "not a record") @@
                 AST.Combinators.get_t_record prev in
               let%bind ty'_map = bind_map_smap translate_type ty_map in
               let%bind path = record_access_to_lr ty' ty'_map prop in
               let path' = List.map snd path in
-              ok (Map.String.find prop ty_map, acc @ path')
-          | Access_map _k -> simple_fail "no patch for map yet"
+            ok (Map.String.find prop ty_map, acc @ path')
+          )
+          | Access_map _k -> fail (corner_case ~loc:__LOC__ "no patch for map yet")
       in
       let%bind (_, path) = bind_fold_right_list aux (ty, []) path in
       let%bind expr' = translate_annotated_expression expr in
@@ -349,9 +443,11 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
             ok (tv' , s') in
           return @@ E_if_none (expr' , n , ((name , tv') , s'))
       | Match_variant (lst , variant) -> (
-          let%bind tree = tree_of_sum variant in
+          let%bind tree =
+            trace_strong (corner_case ~loc:__LOC__ "getting lr tree") @@
+            tree_of_sum variant in
           let%bind tree' = match tree with
-            | Empty -> simple_fail "match empty variant"
+            | Empty -> fail (corner_case ~loc:__LOC__ "match empty variant")
             | Full x -> ok x in
           let%bind tree'' =
             let rec aux t =
@@ -371,7 +467,7 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
             match t with
             | ((`Leaf constructor_name) , tv) -> (
                 let%bind ((_ , name) , body) =
-                  trace_option (simple_error "not supposed to happen here: missing match clause") @@
+                  trace_option (corner_case ~loc:__LOC__ "missing match clause") @@
                   List.find_opt (fun ((constructor_name' , _) , _) -> constructor_name' = constructor_name) lst in
                 let%bind body' = translate_annotated_expression body in
                 return @@ E_let_in ((name , tv) , top , body')
@@ -391,10 +487,11 @@ and translate_annotated_expression (ae:AST.annotated_expression) : expression re
                 in
                 return @@ E_if_left (top , a' , b')
           in
+          trace_strong (corner_case ~loc:__LOC__ "building constructor") @@
           aux expr' tree''
         )
-      | AST.Match_list _ | AST.Match_tuple (_, _) ->
-          simple_fail "only match bool, option and variants are translated yet"
+      | AST.Match_list _ -> fail @@ unsupported_pattern_matching "list" ae.location
+      | AST.Match_tuple _ -> fail @@ unsupported_pattern_matching "tuple" ae.location
     )
 
 and translate_lambda_deep : Mini_c.Environment.t -> AST.lambda -> Mini_c.expression result = fun env l ->
@@ -433,7 +530,6 @@ and translate_lambda env l =
     | [] -> (
         let%bind result' = translate_annotated_expression result in
         let result' = ez_e_return result' in
-        trace (simple_error "translate quote") @@
         let%bind input = translate_type input_type in
         let%bind output = translate_type output_type in
         let tv = Combinators.t_function input output in
@@ -441,7 +537,6 @@ and translate_lambda env l =
         ok @@ Combinators.Expression.make_tpl (E_literal content, tv)
       )
     | _ -> (
-        trace (simple_error "translate lambda deep") @@
         translate_lambda_deep env l
       ) in
   ok result
@@ -463,11 +558,11 @@ let translate_program (lst:AST.program) : program result =
   let%bind (statements, _) = List.fold_left aux (ok ([], Environment.empty)) (temp_unwrap_loc_list lst) in
   ok statements
 
-let translate_main (l:AST.lambda) : anon_function result =
+let translate_main (l:AST.lambda) loc : anon_function result =
   let%bind expr = translate_lambda Environment.empty l in
   match Combinators.Expression.get_content expr with
   | E_literal (D_function f) -> ok f
-  | _ -> simple_fail "main is not a function"
+  | _ -> fail @@ not_functional_main loc
 
 (* From an expression [expr], build the expression [fun () -> expr] *)
 let functionalize (e:AST.annotated_expression) : AST.lambda * AST.type_value =
@@ -484,7 +579,7 @@ let translate_entry (lst:AST.program) (name:string) : anon_function result =
   let rec aux acc (lst:AST.program) =
     let%bind acc = acc in
     match lst with
-    | [] -> simple_fail "no entry point with given name"
+    | [] -> fail @@ missing_entry_point name
     | hd :: tl -> (
         let (AST.Declaration_constant (an , (pre_env , _))) = temp_unwrap_loc hd in
         match an.name = name with
@@ -498,11 +593,11 @@ let translate_entry (lst:AST.program) (name:string) : anon_function result =
             match an.annotated_expression.expression with
             | E_lambda l ->
               let l' = { l with result = acc l.result } in
-              translate_main l'
+              translate_main l' an.annotated_expression.location
             | _ ->
               let (l , _) = functionalize an.annotated_expression in
               let l' = { l with result = acc l.result } in
-              translate_main l'
+              translate_main l' an.annotated_expression.location
           )
       )
   in
@@ -553,36 +648,62 @@ let rec untranspile (v : value) (t : AST.type_value) : AST.annotated_expression
   let open! AST in
   let return e = ok (make_a_e_empty e t) in
   match t.type_value' with
-  | T_constant ("unit", []) ->
-      let%bind () = get_unit v in
+  | T_constant ("unit", []) -> (
+      let%bind () =
+        trace_strong (wrong_mini_c_value "unit" v) @@
+        get_unit v in
       return (E_literal Literal_unit)
-  | T_constant ("bool", []) ->
-      let%bind b = get_bool v in
+    )
+  | T_constant ("bool", []) -> (
+      let%bind b =
+        trace_strong (wrong_mini_c_value "bool" v) @@
+        get_bool v in
       return (E_literal (Literal_bool b))
-  | T_constant ("int", []) ->
-      let%bind n = get_int v in
+    )
+  | T_constant ("int", []) -> (
+      let%bind n =
+        trace_strong (wrong_mini_c_value "int" v) @@
+        get_int v in
       return (E_literal (Literal_int n))
-  | T_constant ("nat", []) ->
-      let%bind n = get_nat v in
+    )
+  | T_constant ("nat", []) -> (
+      let%bind n =
+        trace_strong (wrong_mini_c_value "nat" v) @@
+        get_nat v in      
       return (E_literal (Literal_nat n))
-  | T_constant ("tez", []) ->
-      let%bind n = get_nat v in
+    )
+  | T_constant ("tez", []) -> (
+      let%bind n =
+        trace_strong (wrong_mini_c_value "tez" v) @@
+        get_nat v in
       return (E_literal (Literal_tez n))
-  | T_constant ("string", []) ->
-      let%bind n = get_string v in
+    )
+  | T_constant ("string", []) -> (
+      let%bind n =
+        trace_strong (wrong_mini_c_value "string" v) @@
+        get_string v in
       return (E_literal (Literal_string n))
-  | T_constant ("address", []) ->
-      let%bind n = get_string v in
+    )
+  | T_constant ("address", []) -> (
+      let%bind n =
+        trace_strong (wrong_mini_c_value "address" v) @@
+        get_string v in
       return (E_literal (Literal_address n))
+    )
   | T_constant ("option", [o]) -> (
-      match%bind get_option v with
+      let%bind opt =
+        trace_strong (wrong_mini_c_value "option" v) @@
+        get_option v in
+      match opt with
       | None -> ok (e_a_empty_none o)
       | Some s ->
           let%bind s' = untranspile s o in
           ok (e_a_empty_some s')
     )
   | T_constant ("map", [k_ty;v_ty]) -> (
-      let%bind lst = get_map v in
+      let%bind lst =
+        trace_strong (wrong_mini_c_value "map" v) @@
+        get_map v in
       let%bind lst' =
         let aux = fun (k, v) ->
           let%bind k' = untranspile k k_ty in
@@ -592,48 +713,55 @@ let rec untranspile (v : value) (t : AST.type_value) : AST.annotated_expression
       return (E_map lst')
     )
   | T_constant ("list", [ty]) -> (
-      let%bind lst = get_list v in
+      let%bind lst =
+        trace_strong (wrong_mini_c_value "list" v) @@
+        get_list v in
       let%bind lst' =
         let aux = fun e -> untranspile e ty in
         bind_map_list aux lst in
       return (E_list lst')
     )
   | T_constant ("contract" , [_ty]) ->
-      simple_fail "can't untranspile contract"
-  | T_constant ("operation" , []) ->
-      let%bind op = get_operation v in
+    fail @@ bad_untranspile "contract" v
+  | T_constant ("operation" , []) -> (
+      let%bind op =
+        trace_strong (wrong_mini_c_value "operation" v) @@
+        get_operation v in
       return (E_literal (Literal_operation op))
-  | T_constant (name , lst) ->
-      let error =
-        let title () = "unknown type_constant" in
-        let content () = Format.asprintf "%s (%d)" name (List.length lst) in
-        error title content in
-      fail error
+    )
+  | T_constant (name , _lst) ->
+    fail @@ unknown_untranspile name v
   | T_sum m ->
       let lst = kv_list_of_map m in
       let%bind node = match Append_tree.of_list lst with
-        | Empty -> simple_fail "empty sum type"
+        | Empty -> fail @@ corner_case ~loc:__LOC__ "empty sum type"
         | Full t -> ok t
       in
-      let%bind (name, v, tv) = extract_constructor v node in
+      let%bind (name, v, tv) =
+        trace_strong (corner_case ~loc:__LOC__ "sum extract constructor") @@
+        extract_constructor v node in
       let%bind sub = untranspile v tv in
       return (E_constructor (name, sub))
   | T_tuple lst ->
       let%bind node = match Append_tree.of_list lst with
-        | Empty -> simple_fail "empty tuple"
+        | Empty -> fail @@ corner_case ~loc:__LOC__ "empty tuple"
         | Full t -> ok t in
-      let%bind tpl = extract_tuple v node in
+      let%bind tpl =
+        trace_strong (corner_case ~loc:__LOC__ "tuple extract") @@
+        extract_tuple v node in
       let%bind tpl' = bind_list
         @@ List.map (fun (x, y) -> untranspile x y) tpl in
       return (E_tuple tpl')
   | T_record m ->
       let lst = kv_list_of_map m in
       let%bind node = match Append_tree.of_list lst with
-        | Empty -> simple_fail "empty record"
+        | Empty -> fail @@ corner_case ~loc:__LOC__ "empty record"
         | Full t -> ok t in
-      let%bind lst = extract_record v node in
+      let%bind lst =
+        trace_strong (corner_case ~loc:__LOC__ "record extract") @@
+        extract_record v node in
       let%bind lst = bind_list
         @@ List.map (fun (x, (y, z)) -> let%bind yz = untranspile y z in ok (x, yz)) lst in
       let m' = map_of_kv_list lst in
       return (E_record m')
-  | T_function _ -> simple_fail "no untranspilation for functions yet"
+  | T_function _ -> fail @@ bad_untranspile "function" v