mondo: improve mondo package api + update readme

packages/mondo/README.md

@@ -5,23 +5,32 @@ an experimental parser for an *uzulang*, a custom dsl for patterns that can stan
 - [uzulang I](https://garten.salat.dev/uzu/uzulang1.html)
 - [uzulang II](https://garten.salat.dev/uzu/uzulang2.html)
 
+## Example Usage
+
 ```js
-import { MondoRunner } from 'uzu'
-
-const runner = MondoRunner({ seq, cat, s, crush, speed, '*': fast });
-const pat = runner.run('s [bd hh*2 (cp.crush 4) <mt ht lt>] . speed .8')
-```
-
-the above code will create the following call structure:
-
-```lisp
-(speed 
- (s 
-  (seq bd 
-   (* hh 2) 
-   (crush cp 4) 
-   (cat mt ht lt)
-  )
- ) .8
-)
+import { MondoRunner } from 'mondo'
+// define our library of functions and variables
+let lib = {
+  add: (a, b) => a + b,
+  mul: (a, b) => a * b,
+  PI: Math.PI,
+};
+// this function will evaluate nodes in the syntax tree
+function evaluator(node) {
+  // check if node is a leaf node (!= list)
+  if (node.type !== 'list') {
+    // check lib if we find a match in the lib, otherwise return value
+    return lib[node.value] ?? node.value;
+  }
+  // now it can only be a list..
+  const [fn, ...args] = node.children;
+  // children in a list will already be evaluated
+  // the first child is expected to be a function
+  if (typeof fn !== 'function') {
+    throw new Error(`"${fn}" is not a function ${typeof fn}`);
+  }
+  return fn(...args);
+}
+const runner = new MondoRunner(evaluator);
+const pat = runner.run('add 1 (mul 2 PI)') // 7.283185307179586
 ```