From af68e72f8b6a5f4c97234f6fbeb00d3697e91499 Mon Sep 17 00:00:00 2001
From: Yann Hamdaoui <yann.hamdaoui@tweag.io>
Date: Wed, 14 Feb 2024 09:40:55 +0100
Subject: [PATCH] Implement compilation of enum patterns

---
 core/src/term/pattern/compile.rs | 42 ++++++++++++++++++++++++++++++--
 1 file changed, 40 insertions(+), 2 deletions(-)

diff --git a/core/src/term/pattern/compile.rs b/core/src/term/pattern/compile.rs
index e4dc0bf55d..f32c41ec85 100644
--- a/core/src/term/pattern/compile.rs
+++ b/core/src/term/pattern/compile.rs
@@ -376,8 +376,46 @@ impl CompilePart for RecordPattern {
 }
 
 impl CompilePart for EnumPattern {
-    fn compile_part(&self, _value_id: LocIdent, _bindings_id: LocIdent) -> RichTerm {
-        todo!()
+    fn compile_part(&self, value_id: LocIdent, bindings_id: LocIdent) -> RichTerm {
+        if let Some(pat) = &self.pattern {
+            // if %enum_is_variant% value_id then
+            //   let value_id = %enum_unwrap_variant% value_id in
+            //   <pattern.compile(value_id, bindings_id)>
+            // else
+            //   null
+            make::if_then_else(
+                make::op1(UnaryOp::EnumIsVariant(), Term::Var(value_id)),
+                make::let_in(
+                    value_id,
+                    make::op1(UnaryOp::EnumUnwrapVariant(), Term::Var(value_id)),
+                    pat.compile_part(value_id, bindings_id),
+                ),
+                Term::Null,
+            )
+        } else {
+            // if %typeof% value_id == 'Enum && !(%enum_is_variant% value_id) then
+            //   bindings_id
+            // else
+            //   null
+            make::if_then_else(
+                mk_app!(
+                    make::op1(
+                        UnaryOp::BoolAnd(),
+                        make::op2(
+                            BinaryOp::Eq(),
+                            make::op1(UnaryOp::Typeof(), Term::Var(value_id)),
+                            Term::Enum("Enum".into()),
+                        ),
+                    ),
+                    make::op1(
+                        UnaryOp::BoolNot(),
+                        make::op1(UnaryOp::EnumIsVariant(), Term::Var(value_id))
+                    )
+                ),
+                Term::Var(bindings_id),
+                Term::Null,
+            )
+        }
     }
 }