chain word and better save/load UI

crates/forth/src/vm.rs

@@ -299,6 +299,7 @@ impl Forth {
                     let val = match name.as_str() {
                         "step" => Value::Int(ctx.step as i64, None),
                         "beat" => Value::Float(ctx.beat, None),
+                        "bank" => Value::Int(ctx.bank as i64, None),
                         "pattern" => Value::Int(ctx.pattern as i64, None),
                         "tempo" => Value::Float(ctx.tempo, None),
                         "phase" => Value::Float(ctx.phase, None),
@@ -628,6 +629,24 @@ impl Forth {
                         .insert("__tempo__".to_string(), Value::Float(clamped, None));
                 }
 
+                Op::Chain => {
+                    let pattern = stack.pop().ok_or("stack underflow")?.as_int()? - 1;
+                    let bank = stack.pop().ok_or("stack underflow")?.as_int()? - 1;
+                    if bank < 0 || pattern < 0 {
+                        return Err("chain: bank and pattern must be >= 1".into());
+                    }
+                    if bank as usize == ctx.bank && pattern as usize == ctx.pattern {
+                        // chaining to self is a no-op
+                    } else {
+                        let key = format!("__chain_{}_{}__", ctx.bank, ctx.pattern);
+                        let val = format!("{bank}:{pattern}");
+                        self.vars
+                            .lock()
+                            .unwrap()
+                            .insert(key, Value::Str(val, None));
+                    }
+                }
+
                 Op::ListStart => {
                     stack.push(Value::Marker);
                 }