make separate signal module

packages/core/signal.mjs

@@ -0,0 +1,30 @@
+import { Hap } from './hap.mjs';
+import { Pattern, fastcat } from './pattern.mjs';
+import Fraction from './fraction.mjs';
+
+export function steady(value) {
+  // A continuous value
+  return new Pattern((span) => Hap(undefined, span, value));
+}
+
+export const signal = (func) => {
+  const query = (state) => [new Hap(undefined, state.span, func(state.span.midpoint()))];
+  return new Pattern(query);
+};
+
+export const isaw = signal((t) => 1 - (t % 1));
+export const isaw2 = isaw._toBipolar();
+
+export const saw = signal((t) => t % 1);
+export const saw2 = saw._toBipolar();
+
+export const sine2 = signal((t) => Math.sin(Math.PI * 2 * t));
+export const sine = sine2._fromBipolar();
+export const cosine = sine._early(Fraction(1).div(4));
+export const cosine2 = sine2._early(Fraction(1).div(4));
+
+export const square = signal((t) => Math.floor((t * 2) % 2));
+export const square2 = square._toBipolar();
+
+export const tri = fastcat(isaw, saw);
+export const tri2 = fastcat(isaw2, saw2);