diff --git a/src/passes/2-simplify/pascaligo.ml b/src/passes/2-simplify/pascaligo.ml
index 31e739f36..1d5f1b89b 100644
--- a/src/passes/2-simplify/pascaligo.ml
+++ b/src/passes/2-simplify/pascaligo.ml
@@ -8,7 +8,6 @@ open Combinators
 
 let nseq_to_list (hd, tl) = hd :: tl
 let npseq_to_list (hd, tl) = hd :: (List.map snd tl)
-let npseq_to_nelist (hd, tl) = hd, (List.map snd tl)
 let pseq_to_list = function
   | None -> []
   | Some lst -> npseq_to_list lst
@@ -36,16 +35,6 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let bad_bytes loc str =
-    let title () = "bad bytes string" in
-    let message () =
-      Format.asprintf "bytes string contained non-hexadecimal chars" in
-    let data = [
-      ("location", fun () -> Format.asprintf "%a" Location.pp loc) ;
-      ("bytes", fun () -> str) ;
-    ] in
-    error ~data title message
-
   let unsupported_proc_decl decl =
     let title () = "procedure declarations" in
     let message () =
@@ -88,17 +77,6 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let unsupported_arith_op expr =
-    let title () = "arithmetic expressions" in
-    let message () =
-      Format.asprintf "this arithmetic operator is not supported yet" in
-    let expr_loc = Raw.expr_to_region expr in
-    let data = [
-      ("expr_loc",
-       fun () -> Format.asprintf "%a" Location.pp_lift @@ expr_loc)
-    ] in
-    error ~data title message
-
   let unsupported_string_catenation expr =
     let title () = "string expressions" in
     let message () =
@@ -110,16 +88,6 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let unsupported_proc_calls call =
-    let title () = "procedure calls" in
-    let message () =
-      Format.asprintf "procedure calls are not supported yet" in
-    let data = [
-      ("call_loc",
-       fun () -> Format.asprintf "%a" Location.pp_lift @@ call.Region.region)
-    ] in
-    error ~data title message
-
   let unsupported_for_loops region =
     let title () = "bounded iterators" in
     let message () =
diff --git a/src/passes/2-simplify/pascaligo.mli b/src/passes/2-simplify/pascaligo.mli
new file mode 100644
index 000000000..ebce134d6
--- /dev/null
+++ b/src/passes/2-simplify/pascaligo.mli
@@ -0,0 +1,14 @@
+(** Converts PascaLIGO programs to the Simplified Abstract Syntax Tree. *)
+
+open Ast_simplified
+
+module Raw = Parser.Pascaligo.AST
+module SMap = Map.String
+
+(** Convert a concrete PascaLIGO expression AST to the simplified expression AST 
+    used by the compiler. *)
+val simpl_expression : Raw.expr -> expression Trace.result
+
+(** Convert a concrete PascaLIGO program AST to the simplified program AST used 
+    by the compiler. *)
+val simpl_program : Raw.ast -> program Trace.result