Prolog-ish Livecoding Cheatsheet

New to Prolog? Check out the Full Tutorial for comprehensive explanations!

Core shape

• Facts: kick(t0). — things that are simply true.
• Rules: head :- goal1, goal2. — head is true if all goals are true.
• Queries: ask for solutions to a goal; here the engine repeatedly asks event(Voice, Pitch, Vel, T).
• Variables: Uppercase or _ start, unify with anything. Atoms: lowercase. Numbers: decimals.
• Lists: [a, b, c].

Built-ins (music-focused)

• beat(T, N) – true on N subdivisions per beat.
• phase(T, N, K) – true on step K within N steps per bar.
• every(T, Step) – true on a regular grid of beats (Step in beats).
• prob(P) – passes with probability P (0..1).
• choose(List, X) – nondeterministically unify X with each item.
• pick(List, X) – pick one random element.
• cycle(List, X) – step through list items across calls.
• range(Start, End, Step, X) – count from Start to End by Step.
• rand(Min, Max, X) / randint(Min, Max, X) – random float/int in range.
• eq(A,B) – succeeds if A deep-equals B.
• add(A,B,C) – C = A+B.
• euc(T, K, N, B, R) – Euclidean rhythm, K hits over N steps per bar, B beats/bar, rotation R.
• scale(Root, Mode, Degree, Oct, Midi) – map a scale degree to MIDI.
• chord(Root, Quality, Oct, Midi) – emit chord tones as MIDI numbers.
• transpose(Note, Offset, Out) – add semitones.
• rotate(List, Shift, OutList) – rotate a list.

Event mapping (default)

• The scheduler asks event(Voice, Pitch, Vel, T) every grid tick.
• Voices: kick, snare, hat, sine (Pitch is MIDI for sine).

Mini patterns

% Four-on-the-floor kick
event(kick, 36, 0.95, T) :- euc(T, 4, 16, 4, 0).

% Backbeat snare and busy hats
event(snare, 38, 0.85, T) :- euc(T, 2, 16, 4, 4).
event(hat,   42, 0.25, T) :- euc(T,11, 16, 4, 0).

% Probabilistic ghost hats
event(hat, 46, 0.18, T) :- every(T, 0.125), prob(0.3).

% Bass: pick from a list every half beat
bass(T, N) :- every(T,0.5), pick([40,43,47,48], N).
event(sine, N, 0.55, T) :- bass(T, N).

% Scale lead (major)
lead(T, N) :- every(T,0.25), scale(60, ionian, 1, 0, N).
lead(T, N) :- every(T,0.25), scale(60, ionian, 3, 0, N).
lead(T, N) :- every(T,0.25), scale(60, ionian, 5, 0, N).
event(sine, N, 0.4, T) :- lead(T, N).

% Chord arp (minor triad)
arp(T, N) :- every(T,0.5), chord(57, min, 0, N).
event(sine, N, 0.5, T) :- arp(T, N).

Tips

• Every rule ends with a period .
• Mix deterministic grids (beat/phase/every) with prob for variation.
• Use cycle for predictable motifs, pick/rand for surprise, and euc for quick grooves.
• Adjust Swing/Lookahead in the UI to change feel and scheduling tightness.