Feat: lots of convenience stuff

crates/forth/src/words/compile.rs

@@ -110,6 +110,7 @@ pub(super) fn simple_op(name: &str) -> Option<Op> {
         "mstop" => Op::MidiStop,
         "mcont" => Op::MidiContinue,
         "forget" => Op::Forget,
+        "index" => Op::Index(None),
         "key!" => Op::SetKey,
         "tp" => Op::Transpose,
         "inv" => Op::Invert,
@@ -205,7 +206,8 @@ fn attach_span(op: &mut Op, span: SourceSpan) {
         | Op::Choose(s) | Op::WChoose(s) | Op::Cycle(s) | Op::PCycle(s)
         | Op::Bounce(s) | Op::ChanceExec(s) | Op::ProbExec(s)
         | Op::Every(s)
-        | Op::Bjork(s) | Op::PBjork(s) => *s = Some(span),
+        | Op::Bjork(s) | Op::PBjork(s)
+        | Op::Count(s) | Op::Index(s) => *s = Some(span),
         _ => {}
     }
 }

crates/forth/src/words/sequencing.rs

@@ -113,6 +113,16 @@ pub(super) const WORDS: &[Word] = &[
         compile: Simple,
         varargs: true,
     },
+    Word {
+        name: "index",
+        aliases: &[],
+        category: "Probability",
+        stack: "(v1..vn n idx -- selected)",
+        desc: "Select item at explicit index",
+        example: "[ c4 e4 g4 ] step index",
+        compile: Simple,
+        varargs: true,
+    },
     Word {
         name: "wchoose",
         aliases: &[],