diff --git a/gitlab-pages/docs/language-basics/maps-records.md b/gitlab-pages/docs/language-basics/maps-records.md
index 93bf51fde..26b8abeb5 100644
--- a/gitlab-pages/docs/language-basics/maps-records.md
+++ b/gitlab-pages/docs/language-basics/maps-records.md
@@ -63,7 +63,7 @@ let moves: moveset = Map.literal
 <!--ReasonLIGO-->
 
 ```reasonligo
-let moves: moveset =
+let moves : moveset =
   Map.literal([
     ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address, (1, 2)),
     ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, (0, 3)),
@@ -82,19 +82,19 @@ If we want to access a move from our moveset above, we can use the `[]` operator
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-const balance: option(move) = moves[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)];
+const my_balance : option(move) = moves[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)];
 ```
 
 <!--CameLIGO-->
 
 ```cameligo
-let balance: move option = Map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
+let my_balance : move option = Map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
 ```
 
 <!--ReasonLIGO-->
 
 ```reasonligo
-let balance: option(move) =
+let my_balance : option(move) =
   Map.find_opt("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, moves);
 ```
 <!--END_DOCUSAURUS_CODE_TABS-->
@@ -106,19 +106,19 @@ Accessing a value in a map yields an option, however you can also get the value
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-const balance: move = get_force(("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), moves);
+const my_balance : move = get_force(("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), moves);
 ```
 
 <!--CameLIGO-->
 
 ```cameligo
-let balance: move = Map.find ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
+let my_balance : move = Map.find ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
 ```
 
 <!--ReasonLIGO-->
 
 ```reasonligo
-let balance: move =
+let my_balance : move =
   Map.find("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, moves);
 ```
 
@@ -134,8 +134,8 @@ The values of a PascaLIGO map can be updated using the ordinary assignment synta
 
 ```pascaligo
 
-function set_ (var m: moveset) : moveset is 
-  block { 
+function set_ (var m: moveset) : moveset is
+  block {
     m[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)] := (4,9);
   } with m
 ```
@@ -266,7 +266,7 @@ entries, potentially millions or billions. The cost of loading these entries int
 the environment each time a user executes the contract would eventually become
 too expensive were it not for big maps. Big maps are a data structure offered by
 Tezos which handles the scaling concerns for us. In LIGO, the interface for big
-maps is analogous to the one used for ordinary maps. 
+maps is analogous to the one used for ordinary maps.
 
 Here's how we define a big map:
 
@@ -341,19 +341,19 @@ If we want to access a move from our moveset above, we can use the `[]` operator
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-const balance: option(move) = moves[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)];
+const my_balance : option(move) = moves[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)];
 ```
 
 <!--CameLIGO-->
 
 ```cameligo
-let balance: move option = Big_map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
+let my_balance : move option = Big_map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
 ```
 
 <!--ReasonLIGO-->
 
 ```reasonligo
-let balance: option(move) =
+let my_balance : option(move) =
   Big_map.find_opt("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, moves);
 ```
 <!--END_DOCUSAURUS_CODE_TABS-->
@@ -365,19 +365,19 @@ Accessing a value in a map yields an option, however you can also get the value
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-const balance: move = get_force(("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), moves);
+const my_balance : move = get_force(("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), moves);
 ```
 
 <!--CameLIGO-->
 
 ```cameligo
-let balance: move = Big_map.find ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
+let my_balance : move = Big_map.find ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
 ```
 
 <!--ReasonLIGO-->
 
 ```reasonligo
-let balance: move = Big_map.find("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, moves);
+let my_balance : move = Big_map.find("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address, moves);
 ```
 
 <!--END_DOCUSAURUS_CODE_TABS-->
@@ -392,8 +392,8 @@ The values of a PascaLIGO big map can be updated using the ordinary assignment s
 
 ```pascaligo
 
-function set_ (var m: moveset) : moveset is 
-  block { 
+function set_ (var m : moveset) : moveset is
+  block {
     m[("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)] := (4,9);
   } with m
 ```
@@ -404,7 +404,7 @@ We can update a big map in CameLIGO using the `Big_map.update` built-in:
 
 ```cameligo
 
-let updated_map: moveset =
+let updated_map : moveset =
   Big_map.update ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) (Some (4,9)) moves
 ```
 
@@ -428,7 +428,7 @@ Here's how a custom record type is defined:
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-type user is record 
+type user is record
     id: nat;
     is_admin: bool;
     name: string;
@@ -479,8 +479,8 @@ let user: user = {
 <!--ReasonLIGO-->
 ```reasonligo
 let user: user = {
-  id: 1n, 
-  is_admin: true, 
+  id: 1n,
+  is_admin: true,
   name: "Alice"
 };
 ```
@@ -494,12 +494,12 @@ If we want to obtain a value from a record for a given key, we can do the follow
 <!--DOCUSAURUS_CODE_TABS-->
 <!--Pascaligo-->
 ```pascaligo
-const is_admin: bool = user.is_admin;
+const is_admin : bool = user.is_admin;
 ```
 
 <!--CameLIGO-->
 ```cameligo
-let is_admin: bool = user.is_admin
+let is_admin : bool = user.is_admin
 ```
 
 <!--ReasonLIGO-->
diff --git a/src/passes/1-parser/cameligo/LexToken.mli b/src/passes/1-parser/cameligo/LexToken.mli
index 16a8ac403..79fd2519c 100644
--- a/src/passes/1-parser/cameligo/LexToken.mli
+++ b/src/passes/1-parser/cameligo/LexToken.mli
@@ -137,12 +137,14 @@ type ident_err = Reserved_name
 type   nat_err = Invalid_natural
                | Non_canonical_zero_nat
 type   sym_err = Invalid_symbol
+type   kwd_err = Invalid_keyword
 
 val mk_int    : lexeme -> Region.t -> (token,   int_err) result
 val mk_nat    : lexeme -> Region.t -> (token,   nat_err) result
 val mk_mutez  : lexeme -> Region.t -> (token,   int_err) result
 val mk_ident  : lexeme -> Region.t -> (token, ident_err) result
 val mk_sym    : lexeme -> Region.t -> (token,   sym_err) result
+val mk_kwd    : lexeme -> Region.t -> (token,   kwd_err) result
 val mk_string : lexeme -> Region.t -> token
 val mk_bytes  : lexeme -> Region.t -> token
 val mk_constr : lexeme -> Region.t -> token
diff --git a/src/passes/1-parser/cameligo/LexToken.mll b/src/passes/1-parser/cameligo/LexToken.mll
index 0871c0d32..5c8136624 100644
--- a/src/passes/1-parser/cameligo/LexToken.mll
+++ b/src/passes/1-parser/cameligo/LexToken.mll
@@ -1,4 +1,6 @@
 {
+  (* START HEADER *)
+
 type lexeme = string
 
 let sprintf = Printf.sprintf
@@ -236,8 +238,7 @@ let to_region token = proj_token token |> fst
 
 (* Injections *)
 
-type int_err =
-  Non_canonical_zero
+type int_err = Non_canonical_zero
 
 (* LEXIS *)
 
@@ -258,8 +259,7 @@ let keywords = [
   (fun reg -> Then  reg);
   (fun reg -> True  reg);
   (fun reg -> Type  reg);
-  (fun reg -> With  reg)
-]
+  (fun reg -> With  reg)]
 
 let reserved =
   let open SSet in
@@ -323,8 +323,20 @@ let lexicon : lexis =
       cstr = build constructors;
       res  = reserved}
 
+(* Keywords *)
+
+type kwd_err = Invalid_keyword
+
+let mk_kwd ident region =
+  match SMap.find_opt ident lexicon.kwd with
+    Some mk_kwd -> Ok (mk_kwd region)
+  |        None -> Error Invalid_keyword
+
+(* Identifiers *)
+
 type ident_err = Reserved_name
 
+(* END OF HEADER *)
 }
 
 (* START LEXER DEFINITION *)
diff --git a/src/passes/1-parser/cameligo/ParserMain.ml b/src/passes/1-parser/cameligo/ParserMain.ml
index 855dc639e..f1b03fd25 100644
--- a/src/passes/1-parser/cameligo/ParserMain.ml
+++ b/src/passes/1-parser/cameligo/ParserMain.ml
@@ -19,9 +19,9 @@ module ExtParserLog =
     include ParserLog
   end
 
-module M = ParserUnit.Make (IO)
-                           (Lexer.Make (LexToken))
-                           (AST)
-                           (ExtParser)
-                           (ParErr)
-                           (ExtParserLog)
+module MyLexer = Lexer.Make (LexToken)
+
+module Unit =
+  ParserUnit.Make (IO)(MyLexer)(AST)(ExtParser)(ParErr)(ExtParserLog)
+
+let () = Unit.run ()
diff --git a/src/passes/1-parser/pascaligo.ml b/src/passes/1-parser/pascaligo.ml
index 26447683c..7218acfa4 100644
--- a/src/passes/1-parser/pascaligo.ml
+++ b/src/passes/1-parser/pascaligo.ml
@@ -5,8 +5,9 @@ module AST = Parser_pascaligo.AST
 module ParserLog = Parser_pascaligo.ParserLog
 module LexToken = Parser_pascaligo.LexToken
 module Lexer = Lexer.Make(LexToken)
+module SyntaxError = Parser_pascaligo.SyntaxError
 
-module Errors = struct 
+module Errors = struct
 
   let lexer_error (e: Lexer.error AST.reg) =
     let title () = "lexer error" in
@@ -18,37 +19,39 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let parser_error source (start: Lexing.position) (end_: Lexing.position) lexbuf = 
-    let title () = "parser error" in
-    let file = if source = "" then 
-        "" 
-      else 
-        Format.sprintf "In file \"%s|%s\"" start.pos_fname source
-    in
-    let str = Format.sprintf
-              "Parse error at \"%s\" from (%d, %d) to (%d, %d). %s\n"
-              (Lexing.lexeme lexbuf)
-              start.pos_lnum (start.pos_cnum - start.pos_bol)
-              end_.pos_lnum (end_.pos_cnum - end_.pos_bol)
-              file
-    in
-    let message () = str in
-    let loc = Region.make 
-      ~start:(Pos.from_byte start) 
-      ~stop:(Pos.from_byte end_) 
-    in
+  let reserved_name Region.{value; region} =
+    let title () = Printf.sprintf "reserved name \"%s\"" value in
+    let message () = "" in
     let data = [
-      ("parser_loc", 
-        fun () -> Format.asprintf "%a" Location.pp_lift @@ loc
-      )      
+      ("location",
+       fun () -> Format.asprintf "%a" Location.pp_lift @@ region)
     ] in
     error ~data title message
-  
-  let unrecognized_error source (start: Lexing.position) (end_: Lexing.position) lexbuf = 
-    let title () = "unrecognized error" in
-    let file = if source = "" then 
-        "" 
-      else 
+
+  let duplicate_parameter Region.{value; region} =
+    let title () = Printf.sprintf "duplicate parameter \"%s\"" value in
+    let message () = "" in
+    let data = [
+      ("location",
+       fun () -> Format.asprintf "%a" Location.pp_lift @@ region)
+    ] in
+    error ~data title message
+
+  let duplicate_variant Region.{value; region} =
+    let title () = Printf.sprintf "duplicate variant \"%s\" in this\
+                                   type declaration" value in
+    let message () = "" in
+    let data = [
+      ("location",
+       fun () -> Format.asprintf "%a" Location.pp_lift @@ region)
+    ] in
+    error ~data title message
+
+  let parser_error source (start: Lexing.position) (end_: Lexing.position) lexbuf =
+    let title () = "parser error" in
+    let file = if source = "" then
+        ""
+      else
         Format.sprintf "In file \"%s|%s\"" start.pos_fname source
     in
     let str = Format.sprintf
@@ -59,14 +62,40 @@ module Errors = struct
               file
     in
     let message () = str in
-    let loc = Region.make 
-      ~start:(Pos.from_byte start) 
-      ~stop:(Pos.from_byte end_) 
+    let loc = Region.make
+      ~start:(Pos.from_byte start)
+      ~stop:(Pos.from_byte end_)
     in
     let data = [
-      ("unrecognized_loc", 
+      ("parser_loc",
         fun () -> Format.asprintf "%a" Location.pp_lift @@ loc
-      )      
+      )
+    ] in
+    error ~data title message
+
+  let unrecognized_error source (start: Lexing.position) (end_: Lexing.position) lexbuf =
+    let title () = "unrecognized error" in
+    let file = if source = "" then
+        ""
+      else
+        Format.sprintf "In file \"%s|%s\"" start.pos_fname source
+    in
+    let str = Format.sprintf
+              "Parse error at \"%s\" from (%d, %d) to (%d, %d). %s\n"
+              (Lexing.lexeme lexbuf)
+              start.pos_lnum (start.pos_cnum - start.pos_bol)
+              end_.pos_lnum (end_.pos_cnum - end_.pos_bol)
+              file
+    in
+    let message () = str in
+    let loc = Region.make
+      ~start:(Pos.from_byte start)
+      ~stop:(Pos.from_byte end_)
+    in
+    let data = [
+      ("unrecognized_loc",
+        fun () -> Format.asprintf "%a" Location.pp_lift @@ loc
+      )
     ] in
     error ~data title message
 
@@ -76,19 +105,25 @@ open Errors
 
 type 'a parser = (Lexing.lexbuf -> LexToken.token) -> Lexing.lexbuf -> 'a
 
-let parse (parser: 'a parser) source lexbuf = 
+let parse (parser: 'a parser) source lexbuf =
   let Lexer.{read ; close ; _} = Lexer.open_token_stream None in
-  let result = 
+  let result =
     try
       ok (parser read lexbuf)
     with
-      | Parser.Error ->
+      SyntaxError.Error (Duplicate_parameter name) ->
+        fail @@ (duplicate_parameter name)
+    | SyntaxError.Error (Duplicate_variant name) ->
+        fail @@ (duplicate_variant name)
+    | SyntaxError.Error (Reserved_name name) ->
+        fail @@ (reserved_name name)
+    | Parser.Error ->
         let start = Lexing.lexeme_start_p lexbuf in
         let end_ = Lexing.lexeme_end_p lexbuf in
         fail @@ (parser_error source start end_ lexbuf)
-      | Lexer.Error e ->
+    | Lexer.Error e ->
         fail @@ (lexer_error e)
-      | _ ->
+    | _ ->
         let _ = Printexc.print_backtrace Pervasives.stdout in
         let start = Lexing.lexeme_start_p lexbuf in
         let end_ = Lexing.lexeme_end_p lexbuf in
diff --git a/src/passes/1-parser/pascaligo/AST.ml b/src/passes/1-parser/pascaligo/AST.ml
index 826df1c6d..9aca3eaf3 100644
--- a/src/passes/1-parser/pascaligo/AST.ml
+++ b/src/passes/1-parser/pascaligo/AST.ml
@@ -760,4 +760,49 @@ let rhs_to_region = expr_to_region
 
 let selection_to_region = function
   FieldName {region; _}
-| Component {region; _} -> region
+  | Component {region; _} -> region
+
+(* Extracting variables from patterns *)
+
+module Ord =
+  struct
+    type t = string Region.reg
+    let compare v1 v2 =
+      compare v1.value v2.value
+  end
+
+module VSet = Set.Make (Ord)
+
+let rec vars_of_pattern env = function
+  PConstr p -> vars_of_pconstr env p
+| PVar v -> VSet.add v env
+| PWild _ | PInt _ | PNat _ | PBytes _ | PString _ -> env
+| PList l -> vars_of_plist env l
+| PTuple t -> vars_of_ptuple env t.value
+
+and vars_of_pconstr env = function
+  PUnit _ | PFalse _ | PTrue _ | PNone _ -> env
+| PSomeApp {value=_, {value={inside; _};_}; _} ->
+    vars_of_pattern env inside
+| PConstrApp {value=_, Some tuple; _} ->
+    vars_of_ptuple env tuple.value
+| PConstrApp {value=_,None; _} -> env
+
+and vars_of_plist env = function
+  PListComp {value; _} ->
+    vars_of_pinj env value
+| PNil _ ->
+    env
+| PParCons {value={inside; _}; _} ->
+   let head, _, tail = inside in
+   vars_of_pattern (vars_of_pattern env head) tail
+| PCons {value; _} ->
+    Utils.nsepseq_foldl vars_of_pattern env value
+
+and vars_of_pinj env inj =
+  Utils.sepseq_foldl vars_of_pattern env inj.elements
+
+and vars_of_ptuple env {inside; _} =
+    Utils.nsepseq_foldl vars_of_pattern env inside
+
+let vars_of_pattern = vars_of_pattern VSet.empty
diff --git a/src/passes/1-parser/pascaligo/AST.mli b/src/passes/1-parser/pascaligo/AST.mli
index 5fddb96cb..70620a880 100644
--- a/src/passes/1-parser/pascaligo/AST.mli
+++ b/src/passes/1-parser/pascaligo/AST.mli
@@ -615,3 +615,9 @@ val lhs_to_region        : lhs -> Region.t
 val rhs_to_region        : rhs -> Region.t
 val if_clause_to_region  : if_clause -> Region.t
 val selection_to_region  : selection -> Region.t
+
+(* Extracting variables from patterns *)
+
+module VSet : Set.S with type elt = string Region.reg
+
+val vars_of_pattern : pattern -> VSet.t
diff --git a/src/passes/1-parser/pascaligo/LexToken.mli b/src/passes/1-parser/pascaligo/LexToken.mli
index aa906f8d8..0908eff3f 100644
--- a/src/passes/1-parser/pascaligo/LexToken.mli
+++ b/src/passes/1-parser/pascaligo/LexToken.mli
@@ -138,12 +138,14 @@ type ident_err = Reserved_name
 type   nat_err = Invalid_natural
                | Non_canonical_zero_nat
 type   sym_err = Invalid_symbol
+type   kwd_err = Invalid_keyword
 
 val mk_int    : lexeme -> Region.t -> (token,   int_err) result
 val mk_nat    : lexeme -> Region.t -> (token,   nat_err) result
 val mk_mutez  : lexeme -> Region.t -> (token,   int_err) result
 val mk_ident  : lexeme -> Region.t -> (token, ident_err) result
 val mk_sym    : lexeme -> Region.t -> (token,   sym_err) result
+val mk_kwd    : lexeme -> Region.t -> (token,   kwd_err) result
 val mk_string : lexeme -> Region.t -> token
 val mk_bytes  : lexeme -> Region.t -> token
 val mk_constr : lexeme -> Region.t -> token
diff --git a/src/passes/1-parser/pascaligo/LexToken.mll b/src/passes/1-parser/pascaligo/LexToken.mll
index 090a25825..f1d219655 100644
--- a/src/passes/1-parser/pascaligo/LexToken.mll
+++ b/src/passes/1-parser/pascaligo/LexToken.mll
@@ -389,6 +389,15 @@ let lexicon : lexis =
       cstr = build constructors;
       res  = reserved}
 
+(* Keywords *)
+
+type kwd_err = Invalid_keyword
+
+let mk_kwd ident region =
+  match SMap.find_opt ident lexicon.kwd with
+    Some mk_kwd -> Ok (mk_kwd region)
+  |        None -> Error Invalid_keyword
+
 (* Identifiers *)
 
 type ident_err = Reserved_name
diff --git a/src/passes/1-parser/pascaligo/Parser.mly b/src/passes/1-parser/pascaligo/Parser.mly
index 322198752..efff9226f 100644
--- a/src/passes/1-parser/pascaligo/Parser.mly
+++ b/src/passes/1-parser/pascaligo/Parser.mly
@@ -6,7 +6,60 @@
 open Region
 open AST
 
-(* END HEADER *)
+module SSet = Utils.String.Set
+
+let reserved =
+  let open SSet in
+  empty
+  |> add "get_force"
+  |> add "get_chain_id"
+  |> add "transaction"
+  |> add "get_contract"
+  |> add "get_entrypoint"
+  |> add "size"
+  |> add "int"
+  |> add "abs"
+  |> add "is_nat"
+  |> add "amount"
+  |> add "balance"
+  |> add "now"
+  |> add "unit"
+  |> add "source"
+  |> add "sender"
+  |> add "failwith"
+  |> add "bitwise_or"
+  |> add "bitwise_and"
+  |> add "bitwise_xor"
+  |> add "string_concat"
+  |> add "string_slice"
+  |> add "crypto_check"
+  |> add "crypto_hash_key"
+  |> add "bytes_concat"
+  |> add "bytes_slice"
+  |> add "bytes_pack"
+  |> add "bytes_unpack"
+  |> add "set_empty"
+  |> add "set_mem"
+  |> add "set_add"
+  |> add "set_remove"
+  |> add "set_iter"
+  |> add "set_fold"
+  |> add "list_iter"
+  |> add "list_fold"
+  |> add "list_map"
+  |> add "map_iter"
+  |> add "map_map"
+  |> add "map_fold"
+  |> add "map_remove"
+  |> add "map_update"
+  |> add "map_get"
+  |> add "map_mem"
+  |> add "sha_256"
+  |> add "sha_512"
+  |> add "blake2b"
+  |> add "cons"
+
+ (* END HEADER *)
 %}
 
 (* See [ParToken.mly] for the definition of tokens. *)
@@ -118,6 +171,10 @@ declaration:
 
 type_decl:
   "type" type_name "is" type_expr ";"? {
+    let () =
+      if SSet.mem $2.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $2)) in
     let stop =
       match $5 with
         Some region -> region
@@ -185,6 +242,14 @@ type_tuple:
 
 sum_type:
   "|"? nsepseq(variant,"|") {
+    let add acc {value; _} =
+      if VSet.mem value.constr acc then
+        let open! SyntaxError in
+        raise (Error (Duplicate_variant value.constr))
+      else VSet.add value.constr acc in
+    let variants =
+      Utils.nsepseq_foldl add VSet.empty $2 in
+    let () = ignore variants in
     let region = nsepseq_to_region (fun x -> x.region) $2
     in TSum {region; value=$2} }
 
@@ -225,6 +290,13 @@ fun_expr:
   "function" fun_name? parameters ":" type_expr "is"
      block
   "with" expr {
+    let () =
+      match $2 with
+        Some name ->
+          if SSet.mem name.value reserved then
+            let open! SyntaxError in
+            raise (Error (Reserved_name name))
+      | None -> () in
     let stop   = expr_to_region $9 in
     let region = cover $1 stop
     and value  = {kwd_function = $1;
@@ -237,6 +309,13 @@ fun_expr:
                   return       = $9}
     in {region; value} }
 | "function" fun_name? parameters ":" type_expr "is" expr {
+    let () =
+      match $2 with
+        Some name ->
+          if SSet.mem name.value reserved then
+            let open! SyntaxError in
+            raise (Error (Reserved_name name))
+      | None -> () in
     let stop   = expr_to_region $7 in
     let region = cover $1 stop
     and value  = {kwd_function = $1;
@@ -256,7 +335,7 @@ fun_decl:
   open_fun_decl { $1 }
 | fun_expr ";"  {
     let region = cover $1.region $2
-    and value  = {fun_expr=$1; terminator= Some $2}
+    and value  = {fun_expr=$1; terminator = Some $2}
     in {region; value} }
 
 open_fun_decl:
@@ -266,10 +345,31 @@ open_fun_decl:
     in {region; value} }
 
 parameters:
-  par(nsepseq(param_decl,";")) { $1 }
+  par(nsepseq(param_decl,";")) {
+    let open! AST in
+    let contents : (param_decl, semi) Utils.nsepseq par reg = $1 in
+    let add acc = function
+      ParamConst {value; _} ->
+        if VSet.mem value.var acc then
+          let open! SyntaxError in
+          raise (Error (Duplicate_parameter value.var))
+        else VSet.add value.var acc
+    | ParamVar {value; _} ->
+        if VSet.mem value.var acc then
+          let open! SyntaxError in
+          raise (Error (Duplicate_parameter value.var))
+        else VSet.add value.var acc in
+    let params =
+      Utils.nsepseq_foldl add VSet.empty contents.value.inside in
+    let () = ignore params
+    in $1 }
 
 param_decl:
   "var" var ":" param_type {
+    let () =
+      if SSet.mem $2.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $2)) in
     let stop   = type_expr_to_region $4 in
     let region = cover $1 stop
     and value  = {kwd_var    = $1;
@@ -279,6 +379,10 @@ param_decl:
     in ParamVar {region; value}
   }
 | "const" var ":" param_type {
+    let () =
+      if SSet.mem $2.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $2)) in
     let stop   = type_expr_to_region $4 in
     let region = cover $1 stop
     and value  = {kwd_const  = $1;
@@ -346,13 +450,16 @@ open_var_decl:
 
 unqualified_decl(OP):
   var ":" type_expr OP expr {
+    let () =
+      if SSet.mem $1.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $1)) in
     let region = expr_to_region $5
     in $1, $2, $3, $4, $5, region }
 
 const_decl:
-  open_const_decl { $1 }
-| open_const_decl ";" {
-    {$1 with value = {$1.value with terminator = Some $2}} }
+  open_const_decl ";"? {
+    {$1 with value = {$1.value with terminator=$2}} }
 
 instruction:
   conditional  {        Cond $1 }
@@ -555,6 +662,14 @@ cases(rhs):
 
 case_clause(rhs):
   pattern "->" rhs {
+    let vars = AST.vars_of_pattern $1 in
+    let is_reserved elt = SSet.mem elt.value reserved in
+    let inter = VSet.filter is_reserved vars in
+    let () =
+      if not (VSet.is_empty inter) then
+        let clash = VSet.choose inter in
+        let open! SyntaxError in
+        raise (Error (Reserved_name clash)) in
     fun rhs_to_region ->
       let start  = pattern_to_region $1 in
       let region = cover start (rhs_to_region $3)
@@ -596,6 +711,10 @@ for_loop:
     in For (ForInt {region; value})
   }
 | "for" var arrow_clause? "in" collection expr block {
+    let () =
+      if SSet.mem $2.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $2)) in
     let region = cover $1 $7.region in
     let value  = {kwd_for    = $1;
                   var        = $2;
@@ -613,12 +732,21 @@ collection:
 
 var_assign:
   var ":=" expr {
+    let () =
+      if SSet.mem $1.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $1)) in
     let region = cover $1.region (expr_to_region $3)
     and value  = {name=$1; assign=$2; expr=$3}
     in {region; value} }
 
 arrow_clause:
-  "->" var { $1,$2 }
+  "->" var {
+    let () =
+      if SSet.mem $2.value reserved then
+        let open! SyntaxError in
+        raise (Error (Reserved_name $2))
+    in $1,$2 }
 
 (* Expressions *)
 
@@ -646,7 +774,7 @@ cond_expr:
 
 disj_expr:
   conj_expr { $1 }
-|  disj_expr "or" conj_expr {
+| disj_expr "or" conj_expr {
     let start  = expr_to_region $1
     and stop   = expr_to_region $3 in
     let region = cover start stop
diff --git a/src/passes/1-parser/pascaligo/ParserMain.ml b/src/passes/1-parser/pascaligo/ParserMain.ml
index 3fcae9dec..8ed914f1b 100644
--- a/src/passes/1-parser/pascaligo/ParserMain.ml
+++ b/src/passes/1-parser/pascaligo/ParserMain.ml
@@ -19,9 +19,55 @@ module ExtParserLog =
     include ParserLog
   end
 
-module M = ParserUnit.Make (IO)
-                           (Lexer.Make (LexToken))
-                           (AST)
-                           (ExtParser)
-                           (ParErr)
-                           (ExtParserLog)
+module MyLexer = Lexer.Make (LexToken)
+
+module Unit =
+  ParserUnit.Make (IO)(MyLexer)(AST)(ExtParser)(ParErr)(ExtParserLog)
+
+open! SyntaxError
+
+let () =
+  try Unit.run () with
+    (* Ad hoc errors from the parser *)
+
+    Error (Reserved_name name) ->
+      let () = Unit.close_all () in
+      let token =
+        MyLexer.Token.mk_ident name.Region.value name.Region.region in
+      (match token with
+         Stdlib.Error _ ->
+           assert false (* Should not fail if [name] is valid. *)
+       | Ok invalid ->
+           let point = "Reserved name.\nHint: Change the name.\n",
+                       None, invalid in
+           let error =
+             Unit.format_error ~offsets:IO.options#offsets
+                               IO.options#mode point
+           in Printf.eprintf "\027[31m%s\027[0m%!" error)
+
+  | Error (Duplicate_parameter name) ->
+      let () = Unit.close_all () in
+      let token =
+        MyLexer.Token.mk_ident name.Region.value name.Region.region in
+      (match token with
+         Stdlib.Error _ ->
+           assert false (* Should not fail if [name] is valid. *)
+       | Ok invalid ->
+           let point = "Duplicate parameter.\nHint: Change the name.\n",
+                       None, invalid in
+           let error =
+             Unit.format_error ~offsets:IO.options#offsets
+                               IO.options#mode point
+           in Printf.eprintf "\027[31m%s\027[0m%!" error)
+
+  | Error (Duplicate_variant name) ->
+      let () = Unit.close_all () in
+      let token =
+        MyLexer.Token.mk_constr name.Region.value name.Region.region in
+      let point = "Duplicate variant in this type declaration.\n\
+                   Hint: Change the name.\n",
+                  None, token in
+      let error =
+        Unit.format_error ~offsets:IO.options#offsets
+                          IO.options#mode point
+      in Printf.eprintf "\027[31m%s\027[0m%!" error
diff --git a/src/passes/1-parser/pascaligo/SyntaxError.ml b/src/passes/1-parser/pascaligo/SyntaxError.ml
new file mode 100644
index 000000000..4bdc77d88
--- /dev/null
+++ b/src/passes/1-parser/pascaligo/SyntaxError.ml
@@ -0,0 +1,8 @@
+type t =
+  Reserved_name of string Region.reg
+| Duplicate_parameter of string Region.reg
+| Duplicate_variant of string Region.reg
+
+type error = t
+
+exception Error of t
diff --git a/src/passes/1-parser/pascaligo/SyntaxError.mli b/src/passes/1-parser/pascaligo/SyntaxError.mli
new file mode 100644
index 000000000..4bdc77d88
--- /dev/null
+++ b/src/passes/1-parser/pascaligo/SyntaxError.mli
@@ -0,0 +1,8 @@
+type t =
+  Reserved_name of string Region.reg
+| Duplicate_parameter of string Region.reg
+| Duplicate_variant of string Region.reg
+
+type error = t
+
+exception Error of t
diff --git a/src/passes/1-parser/pascaligo/dune b/src/passes/1-parser/pascaligo/dune
index 1c12ca706..a75445932 100644
--- a/src/passes/1-parser/pascaligo/dune
+++ b/src/passes/1-parser/pascaligo/dune
@@ -8,7 +8,8 @@
 (library
  (name parser_pascaligo)
  (public_name ligo.parser.pascaligo)
- (modules AST pascaligo Parser ParserLog LexToken)
+ (modules
+    SyntaxError AST pascaligo Parser ParserLog LexToken)
  (libraries
     menhirLib
     parser_shared
diff --git a/src/passes/1-parser/reasonligo.ml b/src/passes/1-parser/reasonligo.ml
index e1cbb752a..7bb7ab0cf 100644
--- a/src/passes/1-parser/reasonligo.ml
+++ b/src/passes/1-parser/reasonligo.ml
@@ -29,11 +29,11 @@ module Errors = struct
     ] in
     error ~data title message
 
-  let parser_error source (start: Lexing.position) (end_: Lexing.position) lexbuf = 
+  let parser_error source (start: Lexing.position) (end_: Lexing.position) lexbuf =
     let title () = "parser error" in
-    let file = if source = "" then 
-        "" 
-      else 
+    let file = if source = "" then
+        ""
+      else
         Format.sprintf "In file \"%s|%s\"" start.pos_fname source
     in
     let str = Format.sprintf
@@ -44,22 +44,22 @@ module Errors = struct
               file
     in
     let message () = str in
-    let loc = Region.make 
-      ~start:(Pos.from_byte start) 
-      ~stop:(Pos.from_byte end_) 
+    let loc = Region.make
+      ~start:(Pos.from_byte start)
+      ~stop:(Pos.from_byte end_)
     in
     let data = [
       ("location",
         fun () -> Format.asprintf "%a" Location.pp_lift @@ loc
-      )      
+      )
     ] in
     error ~data title message
-  
-  let unrecognized_error source (start: Lexing.position) (end_: Lexing.position) lexbuf = 
+
+  let unrecognized_error source (start: Lexing.position) (end_: Lexing.position) lexbuf =
     let title () = "unrecognized error" in
-    let file = if source = "" then 
-        "" 
-      else 
+    let file = if source = "" then
+        ""
+      else
         Format.sprintf "In file \"%s|%s\"" start.pos_fname source
     in
     let str = Format.sprintf
@@ -70,14 +70,14 @@ module Errors = struct
               file
     in
     let message () = str in
-    let loc = Region.make 
-      ~start:(Pos.from_byte start) 
-      ~stop:(Pos.from_byte end_) 
+    let loc = Region.make
+      ~start:(Pos.from_byte start)
+      ~stop:(Pos.from_byte end_)
     in
     let data = [
       ("location",
         fun () -> Format.asprintf "%a" Location.pp_lift @@ loc
-      )      
+      )
     ] in
     error ~data title message
 
@@ -87,13 +87,13 @@ open Errors
 
 type 'a parser = (Lexing.lexbuf -> LexToken.token) -> Lexing.lexbuf -> 'a
 
-let parse (parser: 'a parser) source lexbuf = 
+let parse (parser: 'a parser) source lexbuf =
   let Lexer.{read ; close ; _} = Lexer.open_token_stream None in
-  let result = 
+  let result =
     try
       ok (parser read lexbuf)
-    with 
-      | SyntaxError.Error (WrongFunctionArguments e) -> 
+    with
+      | SyntaxError.Error (WrongFunctionArguments e) ->
         fail @@ (wrong_function_arguments e)
       | Parser.Error ->
         let start = Lexing.lexeme_start_p lexbuf in
@@ -110,7 +110,7 @@ let parse (parser: 'a parser) source lexbuf =
   close ();
   result
 
-let parse_file (source: string) : AST.t result =  
+let parse_file (source: string) : AST.t result =
   let pp_input =
     let prefix = Filename.(source |> basename |> remove_extension)
     and suffix = ".pp.religo"
@@ -131,5 +131,5 @@ let parse_string (s:string) : AST.t result =
   parse (Parser.contract) "" lexbuf
 
 let parse_expression (s:string) : AST.expr result =
-  let lexbuf = Lexing.from_string s in  
+  let lexbuf = Lexing.from_string s in
   parse (Parser.interactive_expr) "" lexbuf
diff --git a/src/passes/1-parser/reasonligo/LexToken.mli b/src/passes/1-parser/reasonligo/LexToken.mli
index b5fc9e74d..47f012427 100644
--- a/src/passes/1-parser/reasonligo/LexToken.mli
+++ b/src/passes/1-parser/reasonligo/LexToken.mli
@@ -135,15 +135,17 @@ type ident_err = Reserved_name
 type   nat_err = Invalid_natural
                | Non_canonical_zero_nat
 type   sym_err = Invalid_symbol
+type   kwd_err = Invalid_keyword
 
-val mk_string : lexeme -> Region.t -> token
-val mk_bytes  : lexeme -> Region.t -> token
 val mk_int    : lexeme -> Region.t -> (token,   int_err) result
 val mk_nat    : lexeme -> Region.t -> (token,   nat_err) result
 val mk_mutez  : lexeme -> Region.t -> (token,   int_err) result
 val mk_ident  : lexeme -> Region.t -> (token, ident_err) result
-val mk_constr : lexeme -> Region.t -> token
 val mk_sym    : lexeme -> Region.t -> (token,   sym_err) result
+val mk_kwd    : lexeme -> Region.t -> (token,   kwd_err) result
+val mk_string : lexeme -> Region.t -> token
+val mk_bytes  : lexeme -> Region.t -> token
+val mk_constr : lexeme -> Region.t -> token
 val eof       : Region.t -> token
 
 (* Predicates *)
diff --git a/src/passes/1-parser/reasonligo/LexToken.mll b/src/passes/1-parser/reasonligo/LexToken.mll
index 8525bfce4..4bf6bd8d6 100644
--- a/src/passes/1-parser/reasonligo/LexToken.mll
+++ b/src/passes/1-parser/reasonligo/LexToken.mll
@@ -1,4 +1,6 @@
 {
+(* START OF HEADER *)
+
 type lexeme = string
 
 let sprintf = Printf.sprintf
@@ -91,116 +93,117 @@ type t =
 
 | EOF of Region.t (* End of file *)
 
+
 type token = t
 
 let proj_token = function
-  | CAT region -> region, "CAT"
-  | MINUS region -> region, "MINUS"
-  | PLUS region -> region, "PLUS"
-  | SLASH region -> region, "SLASH"
-  | TIMES region -> region, "TIMES"
-  | LPAR region -> region, "LPAR"
-  | RPAR region -> region, "RPAR"
-  | LBRACKET region -> region, "LBRACKET"
-  | RBRACKET region -> region, "RBRACKET"
-  | LBRACE region -> region, "LBRACE"
-  | RBRACE region -> region, "RBRACE"
-  | COMMA region -> region, "COMMA"
-  | SEMI region -> region, "SEMI"
-  | VBAR region -> region, "VBAR"
-  | COLON region -> region, "COLON"
-  | DOT region -> region, "DOT"
-  | ELLIPSIS region -> region, "ELLIPSIS"
-  | WILD region -> region, "WILD"
-  | EQ region -> region, "EQ"
-  | EQEQ region -> region, "EQEQ"
-  | NE region -> region, "NE"
-  | LT region -> region, "LT"
-  | GT region -> region, "GT"
-  | LE region -> region, "LE"
-  | GE region -> region, "GE"
-  | ARROW region -> region, "ARROW"
-  | BOOL_OR region -> region, "BOOL_OR"
-  | BOOL_AND region -> region, "BOOL_AND"
-  | Ident Region.{region; value} ->
+  CAT region -> region, "CAT"
+| MINUS region -> region, "MINUS"
+| PLUS region -> region, "PLUS"
+| SLASH region -> region, "SLASH"
+| TIMES region -> region, "TIMES"
+| LPAR region -> region, "LPAR"
+| RPAR region -> region, "RPAR"
+| LBRACKET region -> region, "LBRACKET"
+| RBRACKET region -> region, "RBRACKET"
+| LBRACE region -> region, "LBRACE"
+| RBRACE region -> region, "RBRACE"
+| COMMA region -> region, "COMMA"
+| SEMI region -> region, "SEMI"
+| VBAR region -> region, "VBAR"
+| COLON region -> region, "COLON"
+| DOT region -> region, "DOT"
+| ELLIPSIS region -> region, "ELLIPSIS"
+| WILD region -> region, "WILD"
+| EQ region -> region, "EQ"
+| EQEQ region -> region, "EQEQ"
+| NE region -> region, "NE"
+| LT region -> region, "LT"
+| GT region -> region, "GT"
+| LE region -> region, "LE"
+| GE region -> region, "GE"
+| ARROW region -> region, "ARROW"
+| BOOL_OR region -> region, "BOOL_OR"
+| BOOL_AND region -> region, "BOOL_AND"
+| Ident Region.{region; value} ->
     region, sprintf "Ident %s" value
-  | Constr Region.{region; value} ->
+| Constr Region.{region; value} ->
     region, sprintf "Constr %s" value
-  | Int Region.{region; value = s,n} ->
+| Int Region.{region; value = s,n} ->
     region, sprintf "Int (\"%s\", %s)" s (Z.to_string n)
-  | Nat Region.{region; value = s,n} ->
+| Nat Region.{region; value = s,n} ->
     region, sprintf "Nat (\"%s\", %s)" s (Z.to_string n)
-  | Mutez Region.{region; value = s,n} ->
+| Mutez Region.{region; value = s,n} ->
     region, sprintf "Mutez (\"%s\", %s)" s (Z.to_string n)
-  | String Region.{region; value} ->
+| String Region.{region; value} ->
     region, sprintf "String %s" value
-  | Bytes Region.{region; value = s,b} ->
+| Bytes Region.{region; value = s,b} ->
     region,
     sprintf "Bytes (\"%s\", \"0x%s\")"
       s (Hex.to_string b)
-  | Else region -> region, "Else"
-  | False region -> region, "False"
-  | If region -> region, "If"
-  | Let region -> region, "Let"
-  | Switch region -> region, "Switch"
-  | Mod region -> region, "Mod"
-  | NOT region -> region, "!"
-  | Or region -> region, "Or"
-  | True region -> region, "True"
-  | Type region -> region, "Type"
-  | C_None  region -> region, "C_None"
-  | C_Some  region -> region, "C_Some"
-  | EOF region -> region, "EOF"
+| Else region -> region, "Else"
+| False region -> region, "False"
+| If region -> region, "If"
+| Let region -> region, "Let"
+| Switch region -> region, "Switch"
+| Mod region -> region, "Mod"
+| NOT region -> region, "!"
+| Or region -> region, "Or"
+| True region -> region, "True"
+| Type region -> region, "Type"
+| C_None  region -> region, "C_None"
+| C_Some  region -> region, "C_Some"
+| EOF region -> region, "EOF"
 
 let to_lexeme = function
-  | CAT _ -> "++"
-  | MINUS _ -> "-"
-  | PLUS _ -> "+"
-  | SLASH _ -> "/"
-  | TIMES _ -> "*"
-  | LPAR _ -> "("
-  | RPAR _ -> ")"
-  | LBRACKET _ -> "["
-  | RBRACKET _ -> "]"
-  | LBRACE _ -> "{"
-  | RBRACE _ -> "}"
-  | COMMA _ -> ","
-  | SEMI _ -> ";"
-  | VBAR _ -> "|"
-  | COLON _ -> ":"
-  | DOT _ -> "."
-  | ELLIPSIS _ -> "..."
-  | WILD _ -> "_"
-  | EQ _ -> "="
-  | EQEQ _ -> "=="
-  | NE _ -> "!="
-  | LT _ -> "<"
-  | GT _ -> ">"
-  | LE _ -> "<="
-  | GE _ -> ">="
-  | ARROW _ -> "=>"
-  | BOOL_OR _ -> "||"
-  | BOOL_AND _ -> "&&"
-  | Ident id -> id.Region.value
-  | Constr id -> id.Region.value
-  | Int i
-  | Nat i
-  | Mutez i -> fst i.Region.value
-  | String s -> s.Region.value
-  | Bytes b -> fst b.Region.value
-  | Else _ -> "else"
-  | False _ -> "false"
-  | If _ -> "if"
-  | Let _ -> "let"
-  | Mod _ -> "mod"
-  | NOT _ -> "!"
-  | Or _ -> "or"
-  | Switch _ -> "switch"
-  | True _ -> "true"
-  | Type _ -> "type"
-  | C_None  _ -> "None"
-  | C_Some  _ -> "Some"
-  | EOF _ -> ""
+  CAT _ -> "++"
+| MINUS _ -> "-"
+| PLUS _ -> "+"
+| SLASH _ -> "/"
+| TIMES _ -> "*"
+| LPAR _ -> "("
+| RPAR _ -> ")"
+| LBRACKET _ -> "["
+| RBRACKET _ -> "]"
+| LBRACE _ -> "{"
+| RBRACE _ -> "}"
+| COMMA _ -> ","
+| SEMI _ -> ";"
+| VBAR _ -> "|"
+| COLON _ -> ":"
+| DOT _ -> "."
+| ELLIPSIS _ -> "..."
+| WILD _ -> "_"
+| EQ _ -> "="
+| EQEQ _ -> "=="
+| NE _ -> "!="
+| LT _ -> "<"
+| GT _ -> ">"
+| LE _ -> "<="
+| GE _ -> ">="
+| ARROW _ -> "=>"
+| BOOL_OR _ -> "||"
+| BOOL_AND _ -> "&&"
+| Ident id -> id.Region.value
+| Constr id -> id.Region.value
+| Int i
+| Nat i
+| Mutez i -> fst i.Region.value
+| String s -> s.Region.value
+| Bytes b -> fst b.Region.value
+| Else _ -> "else"
+| False _ -> "false"
+| If _ -> "if"
+| Let _ -> "let"
+| Mod _ -> "mod"
+| NOT _ -> "!"
+| Or _ -> "or"
+| Switch _ -> "switch"
+| True _ -> "true"
+| Type _ -> "type"
+| C_None  _ -> "None"
+| C_Some  _ -> "Some"
+| EOF _ -> ""
 
 let to_string token ?(offsets=true) mode =
   let region, val_str = proj_token token in
@@ -216,20 +219,20 @@ type ident_err = Reserved_name
 type   nat_err = Invalid_natural
                | Non_canonical_zero_nat
 type   sym_err = Invalid_symbol
+type   kwd_err = Invalid_keyword
 
 (* LEXIS *)
 
 let keywords = [
-  (fun reg -> Else  reg);
-  (fun reg -> False reg);
-  (fun reg -> If    reg);
-  (fun reg -> Let   reg);
+  (fun reg -> Else   reg);
+  (fun reg -> False  reg);
+  (fun reg -> If     reg);
+  (fun reg -> Let    reg);
   (fun reg -> Switch reg);
-  (fun reg -> Mod   reg);
-  (fun reg -> Or    reg);
-  (fun reg -> True  reg);
-  (fun reg -> Type  reg);
-]
+  (fun reg -> Mod    reg);
+  (fun reg -> Or     reg);
+  (fun reg -> True   reg);
+  (fun reg -> Type   reg)]
 
 (* See: http://caml.inria.fr/pub/docs/manual-ocaml/lex.html#sec86 and
    https://github.com/facebook/reason/blob/master/src/reason-parser/reason_parser.mly *)
@@ -305,6 +308,14 @@ let lexicon : lexis =
       cstr = build constructors;
       res  = reserved}
 
+(* Keywords *)
+
+let mk_kwd ident region =
+  match SMap.find_opt ident lexicon.kwd with
+    Some mk_kwd -> Ok (mk_kwd region)
+  |        None -> Error Invalid_keyword
+
+(* END OF HEADER *)
 }
 
 (* START LEXER DEFINITION *)
@@ -380,40 +391,47 @@ let mk_mutez lexeme region =
 
 let eof region = EOF region
 
+(* Making symbols *)
+
 let mk_sym lexeme region =
   match lexeme with
-    "-"   ->    Ok (MINUS     region)
-  | "+"   ->    Ok (PLUS      region)
-  | "/"   ->    Ok (SLASH     region)
-  | "*"   ->    Ok (TIMES     region)
-  | "["   ->    Ok (LBRACKET  region)
-  | "]"   ->    Ok (RBRACKET  region)
-  | "{"   ->    Ok (LBRACE    region)
-  | "}"  ->     Ok (RBRACE    region)
-  | ","  ->     Ok (COMMA     region)
-  | ";"   ->    Ok (SEMI      region)
-  | "|"   ->    Ok (VBAR      region)
-  | ":"   ->    Ok (COLON     region)
-  | "."  ->     Ok (DOT       region)
-  | "_"   ->    Ok (WILD      region)
-  | "="  ->     Ok (EQ        region)
-  | "!=" ->     Ok (NE        region)
-  | "<"   ->    Ok (LT        region)
-  | ">"   ->    Ok (GT        region)
-  | "<="   ->   Ok (LE        region)
-  | ">="   ->   Ok (GE        region)
-  | "||"   ->   Ok (BOOL_OR   region)
-  | "&&"   ->   Ok (BOOL_AND  region)
-  | "("    ->   Ok (LPAR      region)
-  | ")"    ->   Ok (RPAR      region)
+    "-"  -> Ok (MINUS     region)
+  | "+"  -> Ok (PLUS      region)
+  | "/"  -> Ok (SLASH     region)
+  | "*"  -> Ok (TIMES     region)
+  | "["  -> Ok (LBRACKET  region)
+  | "]"  -> Ok (RBRACKET  region)
+  | "{"  -> Ok (LBRACE    region)
+  | "}"  -> Ok (RBRACE    region)
+  | ","  -> Ok (COMMA     region)
+  | ";"  -> Ok (SEMI      region)
+  | "|"  -> Ok (VBAR      region)
+  | ":"  -> Ok (COLON     region)
+  | "."  -> Ok (DOT       region)
+  | "_"  -> Ok (WILD      region)
+  | "="  -> Ok (EQ        region)
+  | "!=" -> Ok (NE        region)
+  | "<"  -> Ok (LT        region)
+  | ">"  -> Ok (GT        region)
+  | "<=" -> Ok (LE        region)
+  | ">=" -> Ok (GE        region)
+  | "||" -> Ok (BOOL_OR   region)
+  | "&&" -> Ok (BOOL_AND  region)
+  | "("  -> Ok (LPAR      region)
+  | ")"  -> Ok (RPAR      region)
 
   (* Symbols specific to ReasonLIGO *)
-  | "..."->     Ok (ELLIPSIS region)
-  | "=>"    ->  Ok (ARROW     region)
-  | "=="  ->    Ok (EQEQ      region)
-  | "!"    ->   Ok (NOT       region)
-  | "++"   ->   Ok (CAT       region)
-  |  _  ->  Error Invalid_symbol
+
+  | "..." ->  Ok (ELLIPSIS  region)
+  | "=>"  ->  Ok (ARROW     region)
+  | "=="  ->  Ok (EQEQ      region)
+  | "!"   ->  Ok (NOT       region)
+  | "++"  ->  Ok (CAT       region)
+
+  (* Invalid symbols *)
+
+  |     _ ->  Error Invalid_symbol
+
 
 (* Identifiers *)
 
@@ -448,26 +466,26 @@ let is_ident = function
 |       _ -> false
 
 let is_kwd = function
-  | Else _
-  | False _
-  | If _
-  | Let _
-  | Switch _
-  | Mod _
-  | Or _
-  | True _
-  | Type _
-  | _ -> false
+  Else _
+| False _
+| If _
+| Let _
+| Switch _
+| Mod _
+| Or _
+| True _
+| Type _ -> true
+| _ -> false
 
 let is_constr = function
-| Constr  _
+  Constr _
 | Ident _
 | False _
-| True _    -> true
-| _         -> false
+| True _ -> true
+| _ -> false
 
 let is_sym = function
-| CAT _
+  CAT _
 | MINUS _
 | PLUS _
 | SLASH _
diff --git a/src/passes/1-parser/reasonligo/Parser.mly b/src/passes/1-parser/reasonligo/Parser.mly
index 223d35c65..14936a7ff 100644
--- a/src/passes/1-parser/reasonligo/Parser.mly
+++ b/src/passes/1-parser/reasonligo/Parser.mly
@@ -370,7 +370,7 @@ ptuple:
     in PTuple {value=$1; region} }
 
 unit:
-  "(" ")" { {region = cover $1 $2; value = ghost, ghost} }
+  "(" ")" { {region = cover $1 $2; value = $1, $2} }
 
 (* Expressions *)
 
@@ -790,7 +790,7 @@ sequence_or_record_in:
 
 sequence_or_record:
   "{" sequence_or_record_in "}" {
-    let compound = Braces($1, $3) in
+    let compound = Braces ($1,$3) in
     let region   = cover $1 $3 in
     match $2 with
       PaSequence s ->
diff --git a/src/passes/1-parser/reasonligo/ParserMain.ml b/src/passes/1-parser/reasonligo/ParserMain.ml
index ee7d562de..94f437f9d 100644
--- a/src/passes/1-parser/reasonligo/ParserMain.ml
+++ b/src/passes/1-parser/reasonligo/ParserMain.ml
@@ -19,9 +19,26 @@ module ExtParserLog =
     include ParserLog
   end
 
-module M = ParserUnit.Make (IO)
-                           (Lexer.Make (LexToken))
-                           (AST)
-                           (ExtParser)
-                           (ParErr)
-                           (ExtParserLog)
+module MyLexer = Lexer.Make (LexToken)
+
+module Unit =
+  ParserUnit.Make (IO)(MyLexer)(AST)(ExtParser)(ParErr)(ExtParserLog)
+
+(* Main *)
+
+let () =
+  try Unit.run () with
+    (* Ad hoc errors from the parsers *)
+
+    SyntaxError.Error (SyntaxError.WrongFunctionArguments expr) ->
+      let () = Unit.close_all () in
+      let msg = "It looks like you are defining a function, \
+                 however we do not\n\
+                 understand the parameters declaration.\n\
+                 Examples of valid functions:\n\
+                 let x = (a: string, b: int) : int => 3;\n\
+                 let x = (a: string) : string => \"Hello, \" ++ a;\n"
+      and reg = AST.expr_to_region expr in
+      let error = Unit.short_error ~offsets:IO.options#offsets
+                                   IO.options#mode msg reg
+      in Printf.eprintf "\027[31m%s\027[0m%!" error
diff --git a/src/passes/1-parser/reasonligo/SyntaxError.mli b/src/passes/1-parser/reasonligo/SyntaxError.mli
index befbb27c2..f0cc1ca6e 100644
--- a/src/passes/1-parser/reasonligo/SyntaxError.mli
+++ b/src/passes/1-parser/reasonligo/SyntaxError.mli
@@ -1,4 +1,4 @@
-type error = 
+type error =
   | WrongFunctionArguments of AST.expr
 
-exception Error of error
\ No newline at end of file
+exception Error of error
diff --git a/src/passes/1-parser/shared/ParserAPI.ml b/src/passes/1-parser/shared/ParserAPI.ml
index e24be2b48..f8d1520f8 100644
--- a/src/passes/1-parser/shared/ParserAPI.ml
+++ b/src/passes/1-parser/shared/ParserAPI.ml
@@ -1,5 +1,7 @@
 (* Generic parser for LIGO *)
 
+module Region = Simple_utils.Region
+
 module type PARSER =
   sig
     (* The type of tokens, abstract syntax trees and expressions *)
@@ -104,17 +106,22 @@ module Make (Lexer: Lexer.S)
       let trailer =
         match valid_opt with
           None ->
-            if Lexer.Token.is_eof invalid then ""
-            else let invalid_lexeme = Lexer.Token.to_lexeme invalid in
-                 Printf.sprintf ", before \"%s\"" invalid_lexeme
+          if Lexer.Token.is_eof invalid then ""
+          else let invalid_lexeme = Lexer.Token.to_lexeme invalid in
+               Printf.sprintf ", before \"%s\"" invalid_lexeme
         | Some valid ->
-            let valid_lexeme = Lexer.Token.to_lexeme valid in
-            let s = Printf.sprintf ", after \"%s\"" valid_lexeme in
-            if Lexer.Token.is_eof invalid then s
-            else
-              let invalid_lexeme = Lexer.Token.to_lexeme invalid in
-              Printf.sprintf "%s and before \"%s\"" s invalid_lexeme in
+           let valid_lexeme = Lexer.Token.to_lexeme valid in
+           let s = Printf.sprintf ", after \"%s\"" valid_lexeme in
+           if Lexer.Token.is_eof invalid then s
+           else
+             let invalid_lexeme = Lexer.Token.to_lexeme invalid in
+             Printf.sprintf "%s and before \"%s\"" s invalid_lexeme in
       let header = header ^ trailer in
       header ^ (if msg = "" then ".\n" else ":\n" ^ msg)
 
+    let short_error ?(offsets=true) mode msg (invalid_region: Region.t) =
+      let () = assert (not (invalid_region#is_ghost)) in
+      let header =
+        "Parse error " ^ invalid_region#to_string ~offsets mode in
+      header ^ (if msg = "" then ".\n" else ":\n" ^ msg)
   end
diff --git a/src/passes/1-parser/shared/ParserAPI.mli b/src/passes/1-parser/shared/ParserAPI.mli
index 79ca137c4..2c9da70cd 100644
--- a/src/passes/1-parser/shared/ParserAPI.mli
+++ b/src/passes/1-parser/shared/ParserAPI.mli
@@ -1,5 +1,7 @@
 (* Generic parser API for LIGO *)
 
+module Region = Simple_utils.Region
+
 module type PARSER =
   sig
     (* The type of tokens. *)
@@ -56,5 +58,9 @@ module Make (Lexer: Lexer.S)
 
     exception Point of error
 
-    val format_error : ?offsets:bool -> [`Byte | `Point] -> error -> string
+    val format_error :
+      ?offsets:bool -> [`Byte | `Point] -> error -> string
+
+    val short_error :
+      ?offsets:bool -> [`Byte | `Point] -> message -> Region.t -> string
   end
diff --git a/src/passes/1-parser/shared/ParserUnit.ml b/src/passes/1-parser/shared/ParserUnit.ml
index fe1af9559..23e36f494 100644
--- a/src/passes/1-parser/shared/ParserUnit.ml
+++ b/src/passes/1-parser/shared/ParserUnit.ml
@@ -14,7 +14,8 @@ module type Pretty =
       state -> ast -> unit
     val mk_state :
       offsets:bool -> mode:[`Point|`Byte] -> buffer:Buffer.t -> state
-    val print_tokens : state -> ast -> unit
+    val print_tokens :
+      state -> ast -> unit
   end
 
 module Make (IO: S)
@@ -85,6 +86,9 @@ module Make (IO: S)
 
     module ParserFront = ParserAPI.Make (Lexer) (Parser) (ParErr)
 
+    let format_error = ParserFront.format_error
+    let short_error = ParserFront.short_error
+
     let lexer_inst = Lexer.open_token_stream (Some pp_input)
     let Lexer.{read; buffer; get_win; get_pos; get_last; close} = lexer_inst
 
@@ -103,7 +107,7 @@ module Make (IO: S)
 
     (* Main *)
 
-    let () =
+    let run () =
       try
         let ast =
           if   IO.options#mono
@@ -131,37 +135,41 @@ module Make (IO: S)
              end
       with
         (* Lexing errors *)
+
         Lexer.Error err ->
-        close_all ();
-        let msg =
-          Lexer.format_error ~offsets:IO.options#offsets
-                             IO.options#mode err ~file
-        in prerr_string msg
+          close_all ();
+          let msg =
+            Lexer.format_error ~offsets:IO.options#offsets
+                               IO.options#mode err ~file
+          in prerr_string msg
 
       (* Incremental API of Menhir *)
+
       | ParserFront.Point point ->
-         let () = close_all () in
-         let error =
-           ParserFront.format_error ~offsets:IO.options#offsets
-                                    IO.options#mode point
-         in eprintf "\027[31m%s\027[0m%!" error
+          let () = close_all () in
+          let error =
+            ParserFront.format_error ~offsets:IO.options#offsets
+                                     IO.options#mode point
+          in eprintf "\027[31m%s\027[0m%!" error
 
       (* Monolithic API of Menhir *)
+
       | Parser.Error ->
-         let () = close_all () in
-         let invalid, valid_opt =
+          let () = close_all () in
+          let invalid, valid_opt =
            match get_win () with
              Lexer.Nil ->
              assert false (* Safe: There is always at least EOF. *)
            | Lexer.One invalid -> invalid, None
            | Lexer.Two (invalid, valid) -> invalid, Some valid in
-         let point = "", valid_opt, invalid in
-         let error =
-           ParserFront.format_error ~offsets:IO.options#offsets
+          let point = "", valid_opt, invalid in
+          let error =
+            ParserFront.format_error ~offsets:IO.options#offsets
                                     IO.options#mode point
-         in eprintf "\027[31m%s\027[0m%!" error
+          in eprintf "\027[31m%s\027[0m%!" error
 
       (* I/O errors *)
+
       | Sys_error msg -> Utils.highlight msg
 
   end
diff --git a/src/test/contracts/chain_id.ligo b/src/test/contracts/chain_id.ligo
index e7283adf2..7372d8ecc 100644
--- a/src/test/contracts/chain_id.ligo
+++ b/src/test/contracts/chain_id.ligo
@@ -1,5 +1,5 @@
 
-function get_chain_id (const tt : chain_id) : chain_id is
+function chain_id (const tt : chain_id) : chain_id is
   block {
     var toto : chain_id := get_chain_id ;
   } with ( toto )
\ No newline at end of file
diff --git a/src/test/integration_tests.ml b/src/test/integration_tests.ml
index caa4c7c01..9ad2d5026 100644
--- a/src/test/integration_tests.ml
+++ b/src/test/integration_tests.ml
@@ -870,7 +870,7 @@ let map_ type_f path : unit result =
     let make_expected = fun _ -> e_some @@ e_int 4 in
     expect_eq_n program "get_" make_input make_expected
   in
-  let%bind () = 
+  let%bind () =
     let input_map = ez [(23, 10) ; (42, 4)] in
     expect_eq program "mem" (e_tuple [(e_int 23) ; input_map]) (e_bool true)
   in
@@ -1057,27 +1057,27 @@ let loop () : unit result =
     let make_input = e_nat in
     let make_expected = fun n -> e_nat (n * (n + 1) / 2) in
     expect_eq_n_pos_mid program "while_sum" make_input make_expected in
-  let%bind () = 
+  let%bind () =
     let make_input = e_nat in
     let make_expected = fun n -> e_int (n * (n + 1) / 2) in
     expect_eq_n_pos_mid program "for_sum" make_input make_expected in
   let input = e_unit () in
-  let%bind () = 
+  let%bind () =
     let expected = e_pair (e_int 3) (e_string "totototo") in
     expect_eq program "for_collection_list" input expected in
-  let%bind () = 
+  let%bind () =
     let expected = e_pair (e_int 6) (e_string "totototo") in
     expect_eq program "for_collection_set" input expected in
-  let%bind () = 
+  let%bind () =
     let expected = e_pair (e_int 6) (e_string "123") in
     expect_eq program "for_collection_map_kv" input expected in
-  let%bind () = 
+  let%bind () =
     let expected = (e_string "123") in
     expect_eq program "for_collection_map_k" input expected in
-  let%bind () = 
+  let%bind () =
     let expected = (e_int 0) in
     expect_eq program "for_collection_empty" input expected in
-  let%bind () = 
+  let%bind () =
     let expected = (e_int 13) in
     expect_eq program "for_collection_if_and_local_var" input expected in
   let%bind () =
@@ -1680,12 +1680,12 @@ let implicit_account_religo () : unit result =
   ok ()
 
 let tuples_sequences_functions_religo () : unit result =
-  let%bind _ = retype_file "./contracts/tuples_sequences_functions.religo" in    
+  let%bind _ = retype_file "./contracts/tuples_sequences_functions.religo" in
   ok ()
 
 let is_nat () : unit result =
   let%bind program = type_file "./contracts/isnat.ligo" in
-  let%bind () = 
+  let%bind () =
     let input = e_int 10 in
     let expected = e_some (e_nat 10) in
     expect_eq program "main" input expected
@@ -1698,7 +1698,7 @@ let is_nat () : unit result =
 
 let is_nat_mligo () : unit result =
   let%bind program = mtype_file "./contracts/isnat.mligo" in
-  let%bind () = 
+  let%bind () =
     let input = e_int 10 in
     let expected = e_some (e_nat 10) in
     expect_eq program "main" input expected
@@ -1711,7 +1711,7 @@ let is_nat_mligo () : unit result =
 
 let is_nat_religo () : unit result =
   let%bind program = retype_file "./contracts/isnat.religo" in
-  let%bind () = 
+  let%bind () =
     let input = e_int 10 in
     let expected = e_some (e_nat 10) in
     expect_eq program "main" input expected
@@ -1745,7 +1745,7 @@ let deep_access_ligo () : unit result =
     let make_expected = e_string "one" in
     expect_eq program "nested_record" make_input make_expected in
   ok ()
-  
+
 
 let entrypoints_ligo () : unit result =
   let%bind _program = type_file "./contracts/entrypoints.ligo" in
@@ -1759,7 +1759,7 @@ let chain_id () : unit result =
     Tezos_base__TzPervasives.Chain_id.zero in
   let make_input = e_chain_id pouet in
   let make_expected = e_chain_id pouet in
-  let%bind () = expect_eq program "get_chain_id" make_input make_expected in
+  let%bind () = expect_eq program "chain_id" make_input make_expected in
   ok ()
 
 let key_hash () : unit result =
@@ -1830,46 +1830,46 @@ let bytes_unpack () : unit result =
   let%bind () = expect_eq program "id_address" (e_address addr) (e_some (e_address addr)) in
   ok ()
 
-let empty_case () : unit result = 
+let empty_case () : unit result =
   let%bind program = type_file "./contracts/empty_case.ligo" in
   let%bind () =
     let input _ = e_constructor "Bar" (e_int 1) in
-    let expected _ = e_int 1 in 
+    let expected _ = e_int 1 in
     expect_eq_n program "main" input expected
-  in 
+  in
   let%bind () =
     let input _ = e_constructor "Baz" (e_unit ()) in
-    let expected _ = e_int (-1) in 
+    let expected _ = e_int (-1) in
     expect_eq_n program "main" input expected
-  in 
+  in
   ok ()
 
-let empty_case_mligo () : unit result = 
+let empty_case_mligo () : unit result =
   let%bind program = mtype_file "./contracts/empty_case.mligo" in
   let%bind () =
     let input _ = e_constructor "Bar" (e_int 1) in
-    let expected _ = e_int 1 in 
+    let expected _ = e_int 1 in
     expect_eq_n program "main" input expected
-  in 
+  in
   let%bind () =
     let input _ = e_constructor "Baz" (e_unit ()) in
-    let expected _ = e_int (-1) in 
+    let expected _ = e_int (-1) in
     expect_eq_n program "main" input expected
-  in 
+  in
   ok ()
 
-let empty_case_religo () : unit result = 
+let empty_case_religo () : unit result =
   let%bind program = retype_file "./contracts/empty_case.religo" in
   let%bind () =
     let input _ = e_constructor "Bar" (e_int 1) in
-    let expected _ = e_int 1 in 
+    let expected _ = e_int 1 in
     expect_eq_n program "main" input expected
-  in 
+  in
   let%bind () =
     let input _ = e_constructor "Baz" (e_unit ()) in
-    let expected _ = e_int (-1) in 
+    let expected _ = e_int (-1) in
     expect_eq_n program "main" input expected
-  in 
+  in
   ok ()
 
 let main = test_suite "Integration (End to End)" [