From 8275403e955e8998c61ecaa07d70949e3bd53a66 Mon Sep 17 00:00:00 2001
From: Brian Cully <bjc@spork.org>
Date: Mon, 25 Aug 2025 12:25:30 -0400
Subject: tail-position if no longer needs ret

---
 src/forth/compiler.rs |  6 +++---
 src/forth/vm.rs       | 34 +++++++++++++++++++++++-----------
 2 files changed, 26 insertions(+), 14 deletions(-)

(limited to 'src')

diff --git a/src/forth/compiler.rs b/src/forth/compiler.rs
index f593806..e8aaa7f 100644
--- a/src/forth/compiler.rs
+++ b/src/forth/compiler.rs
@@ -133,7 +133,7 @@ impl<'a> Compiler<'a> {
                 self.bc_mut().0.pop();
                 self.bc_mut().0.push(OpCode::TIf(t, f));
                 // technically only needed if ‘f’ is None, but whatever.
-                self.bc_push(OpCode::Ret, anno);
+                //self.bc_push(OpCode::Ret, anno);
             },
             _ => self.bc_push(OpCode::Ret, anno),
         }
@@ -352,7 +352,7 @@ mod tests {
         let main = &comp.wordlist.0[0];
         assert_eq!(main, vec![OpCode::Call(1)]);
         let t = &comp.wordlist.0[1];
-        assert_eq!(t, vec![OpCode::TIf(2, None), OpCode::Ret]);
+        assert_eq!(t, vec![OpCode::TIf(2, None)]);
         let tr = &comp.wordlist.0[2];
         assert_eq!(tr, vec![OpCode::Num(1), OpCode::Num(2), OpCode::Add, OpCode::Ret]);
     }
@@ -365,7 +365,7 @@ mod tests {
         let main = &comp.wordlist.0[0];
         assert_eq!(main, vec![OpCode::Call(1)]);
         let t = &comp.wordlist.0[1];
-        assert_eq!(t, vec![OpCode::TIf(2, Some(3)), OpCode::Ret]);
+        assert_eq!(t, vec![OpCode::TIf(2, Some(3))]);
         let tr = &comp.wordlist.0[2];
         assert_eq!(tr, vec![OpCode::Num(1), OpCode::Num(2), OpCode::Add, OpCode::Ret]);
         let fl = &comp.wordlist.0[3];
diff --git a/src/forth/vm.rs b/src/forth/vm.rs
index 7ce9c03..9c7f203 100644
--- a/src/forth/vm.rs
+++ b/src/forth/vm.rs
@@ -254,6 +254,8 @@ impl VM {
                 } else if let Some(false_clause) = false_clause {
                     self.jmp(false_clause);
                     return Ok(true)
+                } else {
+                    self.ip = self.callstack.0.pop().ok_or(RuntimeError::StackUnderflow)?;
                 }
             },
         }
@@ -501,24 +503,21 @@ mod tests {
 
     #[test]
     fn tail_if_then_false() -> Result<(), RuntimeError> {
-        let mut wordlist = WordList(vec![]);
-        wordlist.0.push(ByteCode(vec![OpCode::Call(1), OpCode::Num(0)]));
-        wordlist.0.push(ByteCode(vec![OpCode::Num(0), OpCode::TIf(2, None), OpCode::Ret]));
-        wordlist.0.push(ByteCode(vec![OpCode::Num(1), OpCode::Ret]));
+        let wordlist = wl_for(vec![
+            vec![OpCode::Call(1), OpCode::Num(0)],
+            vec![OpCode::Num(0), OpCode::TIf(2, None)],
+            vec![OpCode::Num(1), OpCode::Ret],
+        ]);
         let mut vm = VM::new(wordlist);
 
         vm.tick()?;
         assert_eq!(vm.stack.0.len(), 0, "call(1) stack len");
         vm.tick()?;
-        assert_eq!(vm.stack.0.len(), 1, "push 0 stack len");
-        assert_eq!(vm.stack.0[0], 0, "push 0 val");
-        vm.tick()?;
-        assert_eq!(vm.stack.0.len(), 0, "tif stack len");
+        assert_eq!(vm.stack.0, vec![0], "push 0 stack");
         vm.tick()?;
-        assert_eq!(vm.stack.0.len(), 0, "ret stack len");
+        assert_eq!(vm.stack.0, vec![], "tif stack");
         vm.tick()?;
-        assert_eq!(vm.stack.0.len(), 1, "push 0 stack len");
-        assert_eq!(vm.stack.0[0], 0, "push 0 val");
+        assert_eq!(vm.stack.0, vec![0], "push 0 stack");
 
         Ok(())
     }
@@ -599,4 +598,17 @@ mod tests {
         assert_eq!(vm.stack.0, vec![2, 3, 1]);
         Ok(())
     }
+
+    #[test]
+    fn tif_no_ret() -> Result<(), RuntimeError> {
+        let wordlist = wl_for(vec![
+            vec![OpCode::Call(1)],
+            vec![OpCode::Num(0), OpCode::TIf(2, None), OpCode::Num(3)],
+            vec![OpCode::Num(-2)],
+        ]);
+        let mut vm = VM::new(wordlist);
+        vm.run()?;
+        assert_eq!(vm.stack.0, vec![]);
+        Ok(())
+    }
 }
-- 
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