first draft of list splatterns

may_2025_thoughts.md

@@ -240,11 +240,16 @@ println!("{a} // {b_high}/{b_low} // {c}");
 ```
 
 To reiterate the punch list that *I would have needed for Computer Class 1*:
-* [ ] jump instructions need 16 bits of operand
+* [x] jump instructions need 16 bits of operand
+    - Whew, that took longer than I expected
 * [ ] splatterns
     - [ ] validator should ensure splatterns are the longest patterns in a form
-* [ ] add guards to loop forms
-* [ ] check loop forms against function calls: do they still work the way we want them to?
+* [ ] improve validator
+    - [ ] Tuples may not be longer than n members
+    - [ ] Loops may not have splatterns
+    - [ ] Identify others
+* [x] add guards to loop forms
+* [x] check loop forms against function calls: do they still work the way we want them to?
 * [ ] tail call elimination
 * [ ] stack traces in panics
 * [ ] actually good error messages

src/compiler.rs

@@ -42,7 +42,9 @@ pub enum Op {
     PushTuple,
     LoadTuple,
     MatchList,
+    MatchSplattedList,
     LoadList,
+    LoadSplattedList,
     PushList,
     AppendList,
     ConcatList,
@@ -162,7 +164,9 @@ impl std::fmt::Display for Op {
             PushTuple => "push_tuple",
             LoadTuple => "load_tuple",
             MatchList => "match_list",
+            MatchSplattedList => "match_splatted_list",
             LoadList => "load_list",
+            LoadSplattedList => "load_splatted_list",
             PushList => "push_list",
             AppendList => "append_list",
             ConcatList => "concat_list",
@@ -260,9 +264,9 @@ impl Chunk {
                 println!("{i:04}: {:16} {next:03}: {value}", op.to_string());
                 *i += 1;
             }
-            PushBinding | MatchTuple | MatchList | MatchDict | LoadDictValue | PushTuple
-            | PushBox | MatchDepth | PopN | StoreAt | Call | SetUpvalue | GetUpvalue | Partial
-            | MatchString | PushStringMatches => {
+            PushBinding | MatchTuple | MatchList | MatchSplattedList | LoadSplattedList
+            | MatchDict | LoadDictValue | PushTuple | PushBox | MatchDepth | PopN | StoreAt
+            | Call | SetUpvalue | GetUpvalue | Partial | MatchString | PushStringMatches => {
                 let next = self.bytecode[*i + 1];
                 println!("{i:04}: {:16} {next:03}", op.to_string());
                 *i += 1;
@@ -778,7 +782,14 @@ impl<'a> Compiler<'a> {
                 self.match_depth = match_depth + members.len();
             }
             ListPattern(members) => {
+                let mut is_splatted = false;
+                if let Some((Splattern(_), _)) = members.last() {
+                    is_splatted = true;
+                    self.emit_op(Op::MatchSplattedList)
+                } else {
                     self.emit_op(Op::MatchList);
+                }
+                // TODO: lists must be able to be longer than 256 elements; fix this
                 self.emit_byte(members.len());
                 let before_load_tup_idx = self.stub_jump(Op::JumpIfNoMatch);
 
@@ -786,7 +797,12 @@ impl<'a> Compiler<'a> {
                 let match_depth = self.match_depth;
                 self.match_depth = members.len();
 
+                if is_splatted {
+                    self.emit_op(Op::LoadSplattedList);
+                    self.emit_byte(members.len());
+                } else {
                     self.emit_op(Op::LoadList);
+                }
                 self.stack_depth += members.len();
 
                 for member in members {
@@ -841,8 +857,8 @@ impl<'a> Compiler<'a> {
                 self.patch_jump(before_load_dict_idx, self.len() - before_load_dict_idx - 3);
                 self.patch_jump(jump_idx, self.len() - jump_idx - 3);
             }
-            Splattern(..) => {
-                todo!()
+            Splattern(patt) => {
+                self.visit(patt);
             }
             InterpolatedPattern(parts, _) => {
                 println!("An interpolated pattern of {} parts", parts.len());

src/main.rs

@@ -75,10 +75,8 @@ pub fn run(src: &'static str) {
 pub fn main() {
     env::set_var("RUST_BACKTRACE", "1");
     let src = "
-loop (1) with {
-    (0) -> :done
-    (1) -> recur (0)
-}
+let [x, ...y] = [1, 2, 3, 4, 5]
+y
 ";
     run(src);
 }

src/vm.rs

@@ -458,27 +458,51 @@ impl Vm {
                 }
                 MatchList => {
                     let idx = self.stack.len() - self.match_depth as usize - 1;
-                    let tuple_len = self.chunk().bytecode[self.ip + 1];
+                    let list_len = self.chunk().bytecode[self.ip + 1];
                     let scrutinee = self.stack[idx].clone();
                     match scrutinee {
-                        Value::List(members) => self.matches = members.len() == tuple_len as usize,
+                        Value::List(members) => self.matches = members.len() == list_len as usize,
                         _ => self.matches = false,
                     };
                     self.ip += 2;
                 }
+                MatchSplattedList => {
+                    let idx = self.stack.len() - self.match_depth as usize - 1;
+                    let patt_len = self.chunk().bytecode[self.ip + 1];
+                    let scrutinee = self.stack[idx].clone();
+                    match scrutinee {
+                        Value::List(members) => self.matches = members.len() >= patt_len as usize,
+                        _ => self.matches = false,
+                    }
+                    self.ip += 2;
+                }
                 LoadList => {
                     let idx = self.stack.len() - self.match_depth as usize - 1;
-                    let tuple = self.stack[idx].clone();
-                    match tuple {
+                    let list = self.stack[idx].clone();
+                    match list {
                         Value::List(members) => {
                             for member in members.iter() {
                                 self.push(member.clone());
                             }
                         }
-                        _ => return self.panic("internal error: expected tuple"),
+                        _ => return self.panic("internal error: expected list"),
                     };
                     self.ip += 1;
                 }
+                LoadSplattedList => {
+                    let loaded_len = self.chunk().bytecode[self.ip + 1] as usize;
+                    let idx = self.stack.len() - self.match_depth as usize - 1;
+                    let list = self.stack[idx].clone();
+                    let Value::List(members) = list else {
+                        return self.panic("internal error: expected list");
+                    };
+                    for i in 0..loaded_len - 1 {
+                        self.push(members[i].clone());
+                    }
+                    let splatted = Value::List(Box::new(members.skip(loaded_len - 1)));
+                    self.push(splatted);
+                    self.ip += 2;
+                }
                 // PushDict => {
                 //     let dict_len = self.chunk().bytecode[self.ip + 1] as usize * 2;
                 //     let dict_members = self.stack.split_off(self.stack.len() - dict_len);