Lessons · Advanced

Choosing a derivation

Selector patterns over items

% A rule of alternatives is a VOCABULARY of phrases, and a bare
% reference ranges over all of it. 'Fill#n' PINS the n-th derivation in
% enumeration order, so a passage can state which bar it wants.
 
bpm 60
instrument plain
meter 4
unit 1/4
key f# harm
 
Fill ::= kick hat snare hat = kick kick snare hat = kick hat snare snare = snare snare snare snare
 
{Fill#1*3 Fill#2} {Fill#1*3 Fill#4}
 
 
% A pattern segment names an ITEM the derivation must open with, and
% 'any' is a one-item wildcard: 'Fill#kick;any;snare' is "the bar that
% opens kick, anything, snare", chosen by shape, not by list position.
% A number among the segments picks among the matches.
 
Back   ::= Fill#kick;any;snare
Double ::= Fill#kick;kick
Drag   ::= Fill#kick;any;snare;snare
Roll   ::= Fill#snare;snare
 
assert Double == Fill#kick;any;snare;2
{Back*3 Double} {Back*2 Drag Roll}
 
 
% Segments match ITEMS, not tokens. 'kick _2' is ONE position with the
% mark riding its note, so 'kick;snare' finds exactly one of these four
% bars, the first. A rest is a position too, which is why 'kick;any;snare'
% finds two, and only the four-segment 'Gap' reaches the one with the hole.
 
Break    ::= kick _2 snare hat = kick hat snare _2 = kick - snare hat = kick hat hat snare
 
Long     ::= Break#kick;snare
Hold     ::= Break#kick;hat;snare
Gap      ::= Break#kick;any;snare;hat
Straight ::= Break#kick;hat;hat
 
assert Long == Break#1
Long Hold Long Straight Long Hold Gap Straight
 
 
% A melodic vocabulary, and the trap. A segment that is a pure NUMBER is
% a PICK, not a pattern: 'Ans#3' is the third derivation, not "the answer
% opening on the third". And a bare '1' is read as the pick even at the
% end of a pattern, as the second assert below proves. Query on spellings
% that are not bare numbers: an octave prefix ('1, .5, .7) or a drum name.
 
Call ::= 1 _2 3 5 _2 3 2 _2
Ans  ::= '1 5 3 2 1 _4 = 3 2 1 .7 1 _4 = 5 4 3 2 1 _4 = .5 1 3 5 '1 _4
 
Descent ::= Ans#'1
Cadence ::= Ans#any;any;any;.7
Rise    ::= Ans#.5
 
assert Descent == Ans#1
assert Ans#any;any;any;1 == Ans#1
Call Descent Call Cadence
 
 
% Eight drum bars under four melodic phrases, thirty-two units each way,
% the bars and the answers all chosen by name out of a vocabulary. The
% second period rises where the first descended, breaks into the roll, and
% closes on the same cadence.
 
Period  ::= {Long Hold Long Straight Long Hold Gap Straight,
             Call Descent Call Cadence}
Period2 ::= {Long Hold Gap Straight Long Double Drag Roll,
             Call Rise Call Cadence}
 
Period
Period2

% A rule of alternatives is a VOCABULARY of phrases, and a bare
% reference ranges over all of it. 'Fill#n' PINS the n-th derivation in
% enumeration order, so a passage can state which bar it wants.

bpm 60
instrument plain
meter 4
unit 1/4
key f# harm

Fill ::= kick hat snare hat = kick kick snare hat = kick hat snare snare = snare snare snare snare

{Fill#1*3 Fill#2} {Fill#1*3 Fill#4}

% A pattern segment names an ITEM the derivation must open with, and
% 'any' is a one-item wildcard: 'Fill#kick;any;snare' is "the bar that
% opens kick, anything, snare", chosen by shape, not by list position.
% A number among the segments picks among the matches.

Back   ::= Fill#kick;any;snare
Double ::= Fill#kick;kick
Drag   ::= Fill#kick;any;snare;snare
Roll   ::= Fill#snare;snare

assert Double == Fill#kick;any;snare;2
{Back*3 Double} {Back*2 Drag Roll}

% Segments match ITEMS, not tokens. 'kick _2' is ONE position with the
% mark riding its note, so 'kick;snare' finds exactly one of these four
% bars, the first. A rest is a position too, which is why 'kick;any;snare'
% finds two, and only the four-segment 'Gap' reaches the one with the hole.

Break    ::= kick _2 snare hat = kick hat snare _2 = kick - snare hat = kick hat hat snare

Long     ::= Break#kick;snare
Hold     ::= Break#kick;hat;snare
Gap      ::= Break#kick;any;snare;hat
Straight ::= Break#kick;hat;hat

assert Long == Break#1
Long Hold Long Straight Long Hold Gap Straight

% A melodic vocabulary, and the trap. A segment that is a pure NUMBER is
% a PICK, not a pattern: 'Ans#3' is the third derivation, not "the answer
% opening on the third". And a bare '1' is read as the pick even at the
% end of a pattern, as the second assert below proves. Query on spellings
% that are not bare numbers: an octave prefix ('1, .5, .7) or a drum name.

Call ::= 1 _2 3 5 _2 3 2 _2
Ans  ::= '1 5 3 2 1 _4 = 3 2 1 .7 1 _4 = 5 4 3 2 1 _4 = .5 1 3 5 '1 _4

Descent ::= Ans#'1
Cadence ::= Ans#any;any;any;.7
Rise    ::= Ans#.5

assert Descent == Ans#1
assert Ans#any;any;any;1 == Ans#1
Call Descent Call Cadence

% Eight drum bars under four melodic phrases, thirty-two units each way,
% the bars and the answers all chosen by name out of a vocabulary. The
% second period rises where the first descended, breaks into the roll, and
% closes on the same cadence.

Period  ::= {Long Hold Long Straight Long Hold Gap Straight,
             Call Descent Call Cadence}
Period2 ::= {Long Hold Gap Straight Long Double Drag Roll,
             Call Rise Call Cadence}

Period
Period2

running…edit it and it re-runs as you type

Choosing a derivation · Advanced