@resequence/patterns-core

Protocol layer for the pattern system. Base classes, event types, containers, tree utilities, the pitch type system, tuning infrastructure, and type discrimination. This is the extension point for building custom patterns and modifiers.

npm install @resequence/patterns-core

Also available as @resequence/patterns/core or resequence/patterns/core when using the full library or bridge package.

Overview

Every pattern in the resequence ecosystem extends the base classes defined here. This package defines what a pattern is — how it schedules events, composes with other patterns, and carries pitch data. Concrete modifiers and generators live in @resequence/patterns.

Event System

Patterns produce events via schedule(). Events are discriminated on type and bubble up through the tree unchanged.

import type { Event, NoteEvent, MetadataEvent, Keyframe } from "@resequence/patterns-core";

• NoteEvent (type: "note") — pitch, timing, velocity, port routing, slides, CC
• MetadataEvent (type: "metadata") — tempo, time signature, tuning, markers, regions
• BaseEvent — open extension point for custom event types

Base Classes

Pattern — abstract base. Lifecycle: setup(), schedule(), teardown() — all return Event[]. Override _schedule() to emit events.

MidiPattern — extends Pattern with port routing. Notes dispatch to all ports in scope. Defaults to Chromatic tuning.

ModifierPattern — extends MidiPattern. Type marker guaranteeing properties.input exists. The extension point for custom modifiers.

import { Pattern, MidiPattern, ModifierPattern } from "@resequence/patterns-core";

Type Discrimination

Each pattern carries a type tuple for runtime identification:

Pattern.is(p)           // ["pattern", ...]
MidiPattern.is(p)       // ["pattern", "midi", ...]
ModifierPattern.is(p)   // ["pattern", "midi", "modifier", ...]

Containers

import { sequence, layer, gap, toPattern } from "@resequence/patterns-core";

sequence(N.C4(1), N.E4(1), N.G4(2))     // serial — children play one after another
layer(kick, snare, hihat)                 // parallel — children play simultaneously
gap(2)                                    // silence with duration
toPattern(noteOrPattern)                  // normalize Note | Pattern → Pattern

Metadata and Tempo

import { tempo, metadata, timeSignature, marker, cue, region, tuning } from "@resequence/patterns-core";

tempo(pattern, 128);
tempo(pattern, 120, { keyframes: [{ beat: 0, value: 0.5 }, { beat: 16, value: 1.0 }] });
timeSignature(pattern, [3, 4]);
marker(pattern, "chorus");
region(pattern, "verse");
tuning(pattern, customTuning.config);

Pitch

Abstract pitch system supporting arbitrary tuning systems.

import { addSteps, pitchToMidi, pitchKey, pitchToCents } from "@resequence/patterns-core";
import type { Pitch } from "@resequence/patterns-core";

addSteps(pitch, 7)              // shift by 7 steps with octave wrapping
pitchToMidi(pitch, tuning)      // { note, bend } for MIDI output
pitchKey(pitch)                 // single integer key
pitchToCents(a, b)              // distance in cents

Notes

import { note, N, Chromatic } from "@resequence/patterns-core";

N.C4(1)         // quarter note middle C (Chromatic tuning)
N.Fs3(0.5)      // eighth note F#3
note(pitch, 2)  // note from any Pitch object

Chromatic is the built-in 12-TET A=440 tuning. Other tuning presets are in @resequence/patterns-utils.

Tuning System

import { createTuning, createIndexTuning, addAliases } from "@resequence/patterns-core";
import type { Tuning, TuningNote, ResolvedTuning } from "@resequence/patterns-core";

// Equal temperament
const tuning = createTuning({
	classes: ["C", "D", "E", "F", "G", "A", "B"],
	reference: { class: "A", octave: 4, hz: 440 },
});

// Frequency-based
const just = createTuning({
	frequencies: { C: 261.63, D: 294.33, E: 327.03 },
	referenceOctave: 4,
});

// Index-based (for programmatic access)
const indexed = createIndexTuning(12);

Tree Utilities

import { walkPatterns, walkNotes, collectNotes, modifyNotes, flatModifyNotes, modifyPatterns, extentOf } from "@resequence/patterns-core";

walkPatterns(pattern, (p, absoluteBeat) => { /* depth-first */ });
walkNotes(pattern, (note, context) => { /* context.id, context.absoluteBeat */ });
const notes = collectNotes(pattern);
modifyNotes(pattern, (note) => ({ ...note, velocity: 100 }));

Non-Destructive Primitives

import { mute, skip } from "@resequence/patterns-core";

mute(pattern)   // silence without changing duration
skip(pattern)   // zero duration, removed from timeline

Frequency Conversion

Used internally by MidiPattern._schedule():

import { pitchToFrequency, frequencyToNoteAndBend } from "@resequence/patterns-core";

const hz = pitchToFrequency(pitch, tuning);
const { note, bend } = frequencyToNoteAndBend(hz);

Writing Custom Modifiers

Depend on this package to write modifiers without depending on the full library:

import {
	ModifierPattern, ModifierProperties, PatternProperties, Pattern, Note,
	toPattern, modifyNotes,
} from "@resequence/patterns-core";

interface MyModProperties extends ModifierProperties {
	readonly amount: number;
}

class MyModPattern extends ModifierPattern<MyModProperties> {
	readonly type = ["pattern", "midi", "modifier", "myMod"] as const;

	clone(overrides: Partial<PatternProperties>): MyModPattern {
		return new MyModPattern({ ...this.properties, ...overrides });
	}
}

export function myMod(pattern: Pattern | Note, amount: number): MyModPattern {
	const resolved = toPattern(pattern);
	const cloned = resolved.clone({});
	modifyNotes(cloned, (n) => ({ ...n, velocity: n.velocity * amount }));
	return new MyModPattern({
		notes: cloned.notes, children: cloned.children,
		startBeat: cloned.startBeat, endBeat: cloned.endBeat,
		input: resolved, amount,
	});
}