add hooks for scheduler and evaluator

packages/react/src/hooks/useEvaluator.jsx

@@ -0,0 +1,30 @@
+import { useRef, useState, useCallback, useEffect } from 'react';
+
+function useEvaluator(code, evalOnMount = true) {
+  const [error, setError] = useState();
+  const [activeCode, setActiveCode] = useState(code);
+  const [pattern, setPattern] = useState();
+  const isDirty = code !== activeCode;
+  const evaluate = useCallback(() => {
+    try {
+      // TODO: use @strudel.cycles/eval or let user inject custom eval function
+      const _pattern = eval(code);
+      setActiveCode(activeCode);
+      setPattern(_pattern);
+      setError();
+    } catch (err) {
+      setError(err);
+      console.warn('eval error', err);
+    }
+  }, [code, scheduler]);
+  const inited = useRef();
+  useEffect(() => {
+    if (!inited.current && evalOnMount) {
+      evaluate();
+    }
+    inited.current = true;
+  }, [evaluate, evalOnMount]);
+  return { error, evaluate, activeCode, pattern, isDirty };
+}
+
+export default useEvaluator;

packages/react/src/hooks/useScheduler.jsx

@@ -0,0 +1,18 @@
+import { Scheduler } from '@strudel.cycles/core';
+import { useEffect, useMemo, useState } from 'react';
+
+function useScheduler(pattern, defaultOutput, interval = 0.1) {
+  const [error, setError] = useState();
+  // TODO: how / when to remove schedulerError?
+  const scheduler = useMemo(
+    () => new Scheduler({ interval, onTrigger: defaultOutput, onError: setError }),
+    [defaultOutput, interval],
+  );
+  useEffect(() => {
+    // console.log('pattern', pattern);
+    pattern && scheduler?.setPattern(pattern);
+  }, [pattern, scheduler]);
+  return { error, scheduler };
+}
+
+export default useScheduler;