From 56ab4a9fec6d928a2824a5bd5222bd59f1272598 Mon Sep 17 00:00:00 2001
From: butterunderflow <azhong.934@gmail.com>
Date: Wed, 7 Feb 2024 18:58:50 +0800
Subject: [PATCH] let rec expression

---
 lib/syntax/parser.mly  |  1 +
 lib/test/parse_test.ml | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/syntax/parser.mly b/lib/syntax/parser.mly
index 51de560..275ef3d 100644
--- a/lib/syntax/parser.mly
+++ b/lib/syntax/parser.mly
@@ -120,6 +120,7 @@ expr:
     | c=constant { EConst c }
     | v=IDENT { EVar v }
     | LET p=pattern EQ e1=expr IN e2=expr { ELet (p, e1, e2) }
+    | LET REC binds=separated_nonempty_list(AND, function_bind) IN body=expr { ELetrec (binds, body) }
     | tu=tuple_expr { tu }
     | func=expr arg=expr { EApp (func, arg) }
     | LPAREN e=expr RPAREN { e }
diff --git a/lib/test/parse_test.ml b/lib/test/parse_test.ml
index 57cd0df..bfcb1b2 100644
--- a/lib/test/parse_test.ml
+++ b/lib/test/parse_test.ml
@@ -22,10 +22,23 @@ let%expect_test "Test: expression parsing" =
   print_parsed "let x = 1 in y";
   [%expect {| (ELet (PVar x) (EConst (CInt 1)) (EVar y)) |}];
   print_parsed "1,3,4,(5,6),7";
-  [%expect {|
+  [%expect
+    {|
     (ETuple
       ((EConst (CInt 1)) (EConst (CInt 3)) (EConst (CInt 4))
-        (ETuple ((EConst (CInt 5)) (EConst (CInt 6)))) (EConst (CInt 7)))) |}]
+        (ETuple ((EConst (CInt 5)) (EConst (CInt 6)))) (EConst (CInt 7)))) |}];
+  print_parsed
+    {|
+     let rec odd = fun x -> even x
+     and even = fun (x:int) -> odd x
+     in
+     odd 1
+     |};
+  [%expect {|
+    (ELetrec
+      ((odd ((PBare x) (EApp (EVar even) (EVar x))))
+        (even ((PAnn x (TCons int ())) (EApp (EVar odd) (EVar x)))))
+      (EApp (EVar odd) (EConst (CInt 1)))) |}]
 
 let%expect_test "Test: full program parsing" =
   print_parsed_program {|let x = 1|};