ast shape shifting pseudo note variables

repl/src/shapeshifter.js

@@ -0,0 +1,26 @@
+import { parseScript } from './shift-parser/index.js'; // npm module does not work in the browser
+import traverser from './shift-traverser'; // npm module does not work in the browser
+const { replace } = traverser;
+import { LiteralStringExpression, IdentifierExpression } from 'shift-ast';
+import codegen from 'shift-codegen';
+
+const isNote = (name) => /^[a-gC-G][bs]?[0-9]$/.test(name);
+
+export default (code) => {
+  const ast = parseScript(code);
+  const shifted = replace(ast, {
+    enter(node, parent) {
+      // replace identifiers that are a note with a note string
+      if (node.type === 'IdentifierExpression') {
+        if (isNote(node.name)) {
+          const value = node.name[1] === 's' ? node.name.replace('s', '#') : node.name;
+          return new LiteralStringExpression({ value });
+        }
+        if (node.name === 'r') {
+          return new IdentifierExpression({ name: 'silence' });
+        }
+      }
+    },
+  });
+  return codegen(shifted);
+};