feat(compiler)!: Change -> to => in type signatures (#1855)

* feat(compiler)!: Change `->` to `=>` in type signatures

* allow `->`, add some tests

Author: alex-snezhko

compiler/src/formatting/format.re

@@ -1792,7 +1792,7 @@ and print_type =
         },
       ),
       Doc.space,
-      Doc.text("->"),
+      Doc.text("=>"),
       Doc.space,
       print_type(~original_source, ~comments, parsed_type),
     ])

compiler/src/parsing/parser.messages

@@ -348,7 +348,7 @@ program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON UIDENT AS LIDENT YIELD
 ## The known suffix of the stack is as follows:
 ## FOREIGN WASM id_str COLON typ option(as_prefix(id_str))
 ##
-program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON EOL LIDENT ARROW
+program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON EOL LIDENT THICKARROW
 ##
 ## Ends in an error in state: 757.
 ##
@@ -366,7 +366,7 @@ program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON EOL UIDENT AS LIDENT YIELD
 ## The known suffix of the stack is as follows:
 ## FOREIGN WASM id_str COLON eols typ option(as_prefix(id_str))
 ##
-program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON LIDENT ARROW
+program: MODULE UIDENT EOL FOREIGN WASM LIDENT COLON LIDENT THICKARROW
 ##
 ## Ends in an error in state: 749.
 ##
@@ -2884,7 +2884,7 @@ program: MODULE UIDENT EOL UIDENT LPAREN COMMA WHILE
 ## In state 43, spurious reduction of production comma -> COMMA
 ## In state 275, spurious reduction of production option(comma) -> comma
 ##
-program: MODULE UIDENT EOL UIDENT LPAREN UIDENT ARROW
+program: MODULE UIDENT EOL UIDENT LPAREN UIDENT THICKARROW
 ##
 ## Ends in an error in state: 473.
 ##
@@ -3324,7 +3324,7 @@ program: MODULE UIDENT EOL LBRACE BREAK RBRACE LBRACK WASMI64 THICKARROW
 ## In state 243, spurious reduction of production non_stmt_expr -> annotated_expr
 ## In state 62, spurious reduction of production expr -> non_stmt_expr
 ##
-program: MODULE UIDENT EOL PREFIX_150 LBRACK RBRACK LBRACK BIGINT ARROW
+program: MODULE UIDENT EOL PREFIX_150 LBRACK RBRACK LBRACK BIGINT THICKARROW
 ##
 ## Ends in an error in state: 560.
 ##
@@ -3420,7 +3420,7 @@ program: MODULE UIDENT EOL LBRACE LIDENT COMMA EOL LIDENT COLON BREAK WHILE
 ## The known suffix of the stack is as follows:
 ## punned_record_field comma lseparated_nonempty_list_inner(comma,record_field)
 ##
-program: MODULE UIDENT EOL LBRACE ELLIPSIS BIGINT COMMA ELLIPSIS BIGINT ARROW
+program: MODULE UIDENT EOL LBRACE ELLIPSIS BIGINT COMMA ELLIPSIS BIGINT THICKARROW
 ##
 ## Ends in an error in state: 227.
 ##
@@ -3447,7 +3447,7 @@ program: MODULE UIDENT EOL LBRACE ELLIPSIS BIGINT COMMA ELLIPSIS BIGINT ARROW
 
 Expected a comma followed by more record fields or an immediate `}` to complete the record expression.
 
-program: MODULE UIDENT EOL UIDENT LBRACE ELLIPSIS UIDENT ARROW
+program: MODULE UIDENT EOL UIDENT LBRACE ELLIPSIS UIDENT THICKARROW
 ##
 ## Ends in an error in state: 488.
 ##
@@ -3535,7 +3535,7 @@ program: MODULE UIDENT EOL LBRACE LIDENT COMMA LIDENT COMMA EOL WHILE
 
 Expected more record fields or an immediate `}` to complete the record expression.
 
-program: MODULE UIDENT EOL LBRACE ELLIPSIS BIGINT ARROW
+program: MODULE UIDENT EOL LBRACE ELLIPSIS BIGINT THICKARROW
 ##
 ## Ends in an error in state: 222.
 ##
@@ -4402,7 +4402,7 @@ program: MODULE UIDENT EOL LET UIDENT DOT EOL WHILE
 ##
 ## Ends in an error in state: 92.
 ##
-## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT eols . type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS ARROW ]
+## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT eols . type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## lseparated_nonempty_list_inner(dot,type_id_str) DOT eols
@@ -4418,8 +4418,8 @@ program: MODULE UIDENT EOL LET UIDENT DOT WHILE
 ##
 ## Ends in an error in state: 90.
 ##
-## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT . type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS ARROW ]
-## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT . eols type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS ARROW ]
+## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT . type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS THICKARROW ]
+## lseparated_nonempty_list_inner(dot,type_id_str) -> lseparated_nonempty_list_inner(dot,type_id_str) DOT . eols type_id_str [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LPAREN LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DOT DASH COMMA COLON AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## lseparated_nonempty_list_inner(dot,type_id_str) DOT
@@ -4603,7 +4603,7 @@ program: MODULE UIDENT EOL LPAREN WASMI64 EOL WHILE
 ##
 ## Ends in an error in state: 113.
 ##
-## rparen -> eols . RPAREN [ WHILE WHEN WASMI64 WASMI32 WASMF64 WASMF32 VOID UIDENT TYPE TRUE THROW THICKARROW STRING STAR SLASH SEMI RPAREN RECORD RCARET RBRACK RBRACE PREFIX_150 PIPE NUMBER_INT NUMBER_FLOAT MATCH LPAREN LIDENT LET LCARET LBRACKRCARET LBRACK LBRACE INT64 INT32 INFIX_ASSIGNMENT_10 INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 INCLUDE IF GETS FUN FROM FOR FLOAT64 FLOAT32 FALSE FAIL PROVIDE EQUAL EOL EOF ENUM ELSE DOT DASH CONTINUE COMMA COLON CHAR BREAK BIGINT AT ASSERT AS ARROW ]
+## rparen -> eols . RPAREN [ WHILE WHEN WASMI64 WASMI32 WASMF64 WASMF32 VOID UIDENT TYPE TRUE THROW THICKARROW STRING STAR SLASH SEMI RPAREN RECORD RCARET RBRACK RBRACE PREFIX_150 PIPE NUMBER_INT NUMBER_FLOAT MATCH LPAREN LIDENT LET LCARET LBRACKRCARET LBRACK LBRACE INT64 INT32 INFIX_ASSIGNMENT_10 INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 INCLUDE IF GETS FUN FROM FOR FLOAT64 FLOAT32 FALSE FAIL PROVIDE EQUAL EOL EOF ENUM ELSE DOT DASH CONTINUE COMMA COLON CHAR BREAK BIGINT AT ASSERT AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## eols
@@ -5082,7 +5082,7 @@ program: MODULE UIDENT EOL RECORD UIDENT LCARET LIDENT EOL WHILE
 ##
 ## Ends in an error in state: 86.
 ##
-## rcaret -> eols . RCARET [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET LBRACE INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS ARROW ]
+## rcaret -> eols . RCARET [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET LBRACE INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## eols
@@ -5875,7 +5875,7 @@ program: MODULE UIDENT EOL WASMI64 COLON WHILE
 
 Expected a type to complete the type annotation.
 
-program: MODULE UIDENT EOL WASMI64 COLON FUN LIDENT ARROW EOL WHILE
+program: MODULE UIDENT EOL WASMI64 COLON FUN LIDENT THICKARROW EOL WHILE
 ##
 ## Ends in an error in state: 78.
 ##
@@ -5890,9 +5890,9 @@ program: MODULE UIDENT EOL WASMI64 COLON FUN LIDENT ARROW EOL WHILE
 ## may provide an INCOMPLETE view of the future (what was expected next).
 ## In state 3, spurious reduction of production nonempty_list(eol) -> EOL
 ## In state 5, spurious reduction of production eols -> nonempty_list(eol)
-## In state 77, spurious reduction of production arrow -> ARROW eols
+## In state 77, spurious reduction of production arrow -> THICKARROW eols
 ##
-program: MODULE UIDENT EOL WASMI64 COLON FUN LPAREN RPAREN ARROW EOL WHILE
+program: MODULE UIDENT EOL WASMI64 COLON FUN LPAREN RPAREN THICKARROW EOL WHILE
 ##
 ## Ends in an error in state: 122.
 ##
@@ -5907,7 +5907,22 @@ program: MODULE UIDENT EOL WASMI64 COLON FUN LPAREN RPAREN ARROW EOL WHILE
 ## may provide an INCOMPLETE view of the future (what was expected next).
 ## In state 3, spurious reduction of production nonempty_list(eol) -> EOL
 ## In state 5, spurious reduction of production eols -> nonempty_list(eol)
-## In state 77, spurious reduction of production arrow -> ARROW eols
+## In state 77, spurious reduction of production arrow -> THICKARROW eols
+##
+program: MODULE UIDENT EOL UIDENT COLON FUN UIDENT THICKARROW YIELD
+##
+## Ends in an error in state: 217.
+##
+## typ -> FUN data_typ thickarrow . typ [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS AND ]
+##
+## The known suffix of the stack is as follows:
+## FUN data_typ thickarrow
+##
+## WARNING: This example involves spurious reductions.
+## This implies that, although the LR(1) items shown above provide an
+## accurate view of the past (what has been recognized so far), they
+## may provide an INCOMPLETE view of the future (what was expected next).
+## In state 37, spurious reduction of production thickarrow -> THICKARROW
 ##
 
 Expected a type for the result of the function type.
@@ -6095,31 +6110,31 @@ program: MODULE UIDENT EOL WASMI64 COLON LPAREN UIDENT WHEN
 
 Expected `)` for a grouped type or a comma followed by more types for a tuple type.
 
-program: MODULE UIDENT EOL WASMI64 COLON UIDENT ARROW EOL WHILE
+program: MODULE UIDENT EOL UIDENT COLON FUN UIDENT YIELD
 ##
-## Ends in an error in state: 107.
+## Ends in an error in state: 216.
 ##
-## typ -> data_typ arrow . typ [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS ]
+## typ -> FUN data_typ . thickarrow typ [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS AND ]
 ##
 ## The known suffix of the stack is as follows:
-## data_typ arrow
+## FUN data_typ
 ##
 ## WARNING: This example involves spurious reductions.
 ## This implies that, although the LR(1) items shown above provide an
 ## accurate view of the past (what has been recognized so far), they
 ## may provide an INCOMPLETE view of the future (what was expected next).
-## In state 3, spurious reduction of production nonempty_list(eol) -> EOL
-## In state 5, spurious reduction of production eols -> nonempty_list(eol)
-## In state 77, spurious reduction of production arrow -> ARROW eols
+## In state 106, spurious reduction of production qualified_uid -> lseparated_nonempty_list_inner(dot,type_id_str)
+## In state 167, spurious reduction of production data_typ -> qualified_uid
 ##
 
-Expected a type for the result of the function type.
+# This error can't appear as the FUN token wouldn't have been injected.
+Expected `=>` followed by the function type's result type.
 
 program: MODULE UIDENT EOL WASMI64 COLON UIDENT LCARET EOL WHILE
 ##
 ## Ends in an error in state: 82.
 ##
-## data_typ -> type_id lcaret . typs rcaret [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS ARROW ]
+## data_typ -> type_id lcaret . typs rcaret [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## type_id lcaret
@@ -6139,7 +6154,7 @@ program: MODULE UIDENT EOL WASMI64 COLON UIDENT LCARET UIDENT RPAREN
 ##
 ## Ends in an error in state: 83.
 ##
-## data_typ -> type_id lcaret typs . rcaret [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS ARROW ]
+## data_typ -> type_id lcaret typs . rcaret [ WHEN THICKARROW STAR SLASH SEMI RPAREN RCARET RBRACK RBRACE PIPE LCARET INFIX_90 INFIX_80 INFIX_70 INFIX_60 INFIX_50 INFIX_40 INFIX_30 INFIX_120 INFIX_110 INFIX_100 FROM EQUAL EOL EOF ELSE DASH COMMA COLON AS THICKARROW ]
 ##
 ## The known suffix of the stack is as follows:
 ## type_id lcaret typs

compiler/src/parsing/parser.mly

@@ -195,6 +195,10 @@ arrow:
 thickarrow:
   | THICKARROW opt_eols {}
 
+either_arrow:
+  | arrow {}
+  | thickarrow {}
+
 equal:
   | EQUAL opt_eols {}
 
@@ -299,9 +303,9 @@ data_typ:
   | qualified_uid %prec _below_infix { Type.constr ~loc:(to_loc $loc) $1 [] }
 
 typ:
-  | data_typ arrow typ { Type.arrow ~loc:(to_loc $loc) [TypeArgument.mk ~loc:(to_loc $loc($1)) Unlabeled $1] $3 }
-  | FUN LIDENT arrow typ { Type.arrow ~loc:(to_loc $loc) [TypeArgument.mk ~loc:(to_loc $loc($2)) Unlabeled (Type.var $2)] $4 }
-  | FUN lparen arg_typs? rparen arrow typ { Type.arrow ~loc:(to_loc $loc) (Option.value ~default:[] $3) $6 }
+  | FUN data_typ either_arrow typ { Type.arrow ~loc:(to_loc $loc) [TypeArgument.mk ~loc:(to_loc $loc($2)) Unlabeled $2] $4 }
+  | FUN LIDENT either_arrow typ { Type.arrow ~loc:(to_loc $loc) [TypeArgument.mk ~loc:(to_loc $loc($2)) Unlabeled (Type.var $2)] $4 }
+  | FUN lparen arg_typs? rparen either_arrow typ { Type.arrow ~loc:(to_loc $loc) (Option.value ~default:[] $3) $6 }
   | lparen tuple_typs rparen { Type.tuple ~loc:(to_loc $loc) $2 }
   | lparen typ rparen { $2 }
   | LIDENT { Type.var ~loc:(to_loc $loc) $1 }

compiler/src/parsing/wrapped_lexer.re

@@ -58,6 +58,7 @@ let fake_triple = (t, (_, pos, _)) => (t, pos, pos);
 
 exception Lex_balanced_failed(list(positioned(token)), option(exn));
 exception Lex_fast_forward_failed(list(positioned(token)), option(exn));
+exception Lex_data_typ_failed(list(positioned(token)), option(exn));
 
 let inject_fun =
   fun
@@ -144,12 +145,29 @@ and check_id_fn = (state, closing, acc) => {
   lex_balanced_step(state, closing, acc, tok);
 }
 
+and check_data_typ = (state, closing, acc) => {
+  switch (lex_data_typ(state)) {
+  | exception (Lex_data_typ_failed([token, ...rest], exn)) =>
+    lex_balanced_step(state, closing, rest @ acc, token)
+  | [token, ...rest] =>
+    let acc =
+      if (is_triggering_token(token)) {
+        inject_fun(acc);
+      } else {
+        acc;
+      };
+    lex_balanced_step(state, closing, rest @ acc, token);
+  | _ => failwith("Impossible: wrapped_lexer check_data_typ not matched")
+  };
+}
+
 and lex_balanced_step = (state, closing, acc, tok) => {
   let acc = [tok, ...acc];
   switch (tok, closing) {
   | ((RPAREN, _, _), RPAREN)
   | ((RBRACE, _, _), RBRACE)
-  | ((RBRACK, _, _), RBRACK) =>
+  | ((RBRACK, _, _), RBRACK)
+  | ((RCARET, _, _), RCARET) =>
     pop_fn_ctx(state);
     acc;
   | ((RPAREN | RBRACE | RBRACK | EOF, _, _), _) =>
@@ -182,6 +200,7 @@ and lex_balanced_step = (state, closing, acc, tok) => {
     | LPAREN => check_lparen_fn(state, closing, [triple', ...tokens @ acc])
     | LIDENT(_)
     | UNDERSCORE => check_id_fn(state, closing, [triple', ...tokens @ acc])
+    | UIDENT(_) => check_data_typ(state, closing, [triple', ...tokens @ acc])
     | _ =>
       // Recurse normally
       lex_balanced_step(state, closing, tokens @ acc, triple')
@@ -208,6 +227,8 @@ and lex_balanced_step = (state, closing, acc, tok) => {
     )
   | ((LIDENT(_) | UNDERSCORE, _, _), _) when !ignore_fns(state) =>
     check_id_fn(state, closing, acc)
+  | ((UIDENT(_), p, _), _) when !ignore_fns(state) =>
+    check_data_typ(state, closing, acc)
   | _ => lex_balanced(state, closing, acc)
   };
 }
@@ -244,6 +265,52 @@ and lookahead_fun = (state, (tok, _, _) as lparen) =>
     }
   }
 
+and lex_qualified_uid = (state, acc) => {
+  switch (token(state)) {
+  | exception exn => raise(Lex_data_typ_failed(acc, Some(exn)))
+  | (DOT, _, _) as dot =>
+    switch (token(state)) {
+    | exception exn => raise(Lex_data_typ_failed(acc, Some(exn)))
+    | (UIDENT(_), _, _) as uident =>
+      lex_qualified_uid(state, [uident, dot, ...acc])
+    | tok => raise(Lex_data_typ_failed([tok, dot, ...acc], None))
+    }
+  | token => [token, ...acc]
+  };
+}
+
+and lex_data_typ = state => {
+  switch (lex_qualified_uid(state, [])) {
+  | [(LCARET, _, _), ..._] as quid_tokens =>
+    switch (lex_balanced(~push=DiscoverFunctions, state, RCARET, [])) {
+    | exception (Lex_balanced_failed(tokens, exn)) =>
+      raise(Lex_data_typ_failed(tokens, exn))
+    | brack_tokens =>
+      let tokens = brack_tokens @ quid_tokens;
+      switch (token(state)) {
+      | exception exn => raise(Lex_data_typ_failed(tokens, Some(exn)))
+      | tok => [tok, ...tokens]
+      };
+    }
+  | tokens => tokens
+  };
+}
+
+and lookahead_fun_data_typ = (state, uident) => {
+  switch (lex_data_typ(state)) {
+  | exception (Lex_data_typ_failed(tokens, exn)) =>
+    state.queued_tokens = List.rev(tokens);
+    state.queued_exn = exn;
+    uident;
+  | [token, ..._] as tokens when is_triggering_token(token) =>
+    state.queued_tokens = [uident, ...List.rev(tokens)];
+    fake_triple(FUN, uident);
+  | tokens =>
+    state.queued_tokens = List.rev(tokens);
+    uident;
+  };
+}
+
 and lookahead_match = state => {
   switch (lex_fast_forward(state, LPAREN, [])) {
   | exception (Lex_fast_forward_failed(tokens, exn)) =>
@@ -307,6 +374,7 @@ let token = state => {
           tok;
         }
       }
+    | (UIDENT(_), _, _) as tok => lookahead_fun_data_typ(state, tok)
     | token => token
     }
   | ([x, ...xs], _) =>

compiler/src/typed/oprint.re

@@ -367,7 +367,7 @@ and print_out_type_1 = ppf =>
       if (parens) {
         pp_print_char(ppf, ')');
       };
-      pp_print_string(ppf, " ->");
+      pp_print_string(ppf, " =>");
       pp_print_space(ppf, ());
       print_out_type_1(ppf, ty2);
       pp_close_box(ppf, ());

compiler/test/graindoc/descriptions.expected.md

@@ -49,7 +49,7 @@ Value Doc
 ### DescriptionGrainDoc.**docFunction**
 
 ```grain
-docFunction : (x: Number) -> Number
+docFunction : (x: Number) => Number
 ```
 
 Function Doc