From 540e4199d1e777bb961475674080e6a442ada2d6 Mon Sep 17 00:00:00 2001
From: Kai Schmidt <kaikaliischmidt@gmail.com>
Date: Tue, 5 Nov 2024 16:25:05 -0800
Subject: [PATCH] fix a bug in a fork optimization

---
 src/compile/modifier.rs | 7 ++++---
 tests/optimized.ua      | 4 ++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/compile/modifier.rs b/src/compile/modifier.rs
index d3eaf02ff..15d8e6570 100644
--- a/src/compile/modifier.rs
+++ b/src/compile/modifier.rs
@@ -453,9 +453,10 @@ impl Compiler {
                     );
                 }
                 let span = self.add_span(modified.modifier.span.clone());
-                match f.sig.args {
-                    0 => Node::from_iter([g.node, f.node]),
-                    1 => Node::from_iter([Node::Mod(On, eco_vec![g], span), f.node]),
+                match (f.sig.args, g.sig.args) {
+                    (0, _) => Node::from_iter([g.node, f.node]),
+                    (1, 0) => Node::from_iter([Node::Mod(Dip, eco_vec![g], span), f.node]),
+                    (1, _) => Node::from_iter([Node::Mod(On, eco_vec![g], span), f.node]),
                     _ => Node::Mod(Fork, eco_vec![f, g], span),
                 }
             }
diff --git a/tests/optimized.ua b/tests/optimized.ua
index ec464e204..8b3dd25c7 100644
--- a/tests/optimized.ua
+++ b/tests/optimized.ua
@@ -81,6 +81,10 @@
 ⍤⤙≍ [⊞⊃+- .⇡5] [⊞⊃(+|-) .⇡5]
 ⍤⤙≍ {⊞(∘⊃(+|++))..⇡2} {⊞⊃(+|++)..⇡2}
 
+# Fork reductions
+⍤⤙≍ [5 ¯3] [⊃5¯] 3
+⍤⤙≍ [¯3 5] [⊃¯ 5] 3
+
 ⍤⤙≍ [0 0 0] ≡⋅0 ⇡3
 ⍤⤙≍ [0 0 0] ∵⋅0 ⇡3
 ⍤⤙≍ [0 0 0] ≡⋅0 ↯3_3 0