Lessons · Grammars

Using grammars

Rules, composites, enumeration

% A grammar line NAMES material with '::=', and every uppercase token is
% a REFERENCE that expands to the named material inline. Nothing here is
% written twice: Tune names the four-bar melody, Walk the bass under it,
% Beat one measure of the groove, and Verse superposes all three. Naming
% sounds nothing by itself — the last line STATES Verse, and that plays.
 
bpm 75
meter 4
unit 1/4
key g4 harm
 
Tune ::= | 1 2 3 4 |
         | 5 _2 4 3 |
         | 6 5 4 3 |
         | 2 _3 .7 |
Walk ::= | .1 _2 .5 .1 |
         | .4 _2 .1 .4 |
         | .5 _2 .2 .5 |
         | .1 _2 .4 .5 |
Beat ::= | kick hat snare hat kick kick snare hat |
 
assert Beat*4 == Beat Beat Beat Beat
 
Verse ::= {Tune, Walk, Beat*4}
 
Verse
 
 
% Marks after a reference cover the WHOLE expansion, so one rule states
% several passages. Climb is those same four bars two scale steps up —
% the key decides where the half steps land — and Retro is those bars
% backwards, durations kept, so the melody opens on the leading tone and
% lands on the tonic:
 
Climb ::= {Tune@~2, Walk@~2, Beat*4}
Retro ::= {Tune~, Walk, Beat*4}
 
Climb
Retro
 
 
% '=' separates ALTERNATIVES: one name, three bodies. Tag is how the
% phrase ends over the cadence bass — closed on the tonic, open on the
% fifth, soft on the third. 'enum' lists each distinct derivation with
% its own ▶, and a plain reference takes the first, which the assert
% below states in the language:
 
Tag ::= | 2 _2 .7 2 | 1 _4 |
      = | 2 _2 .7 2 | 5 _4 |
      = | 4 _2 3 2 | 3 _4 |
Cad ::= | .5 _2 .2 .5 | .1 _4 |
 
enum Tag
assert Tag == Tag#1
 
Verse {Tag, Cad, Beat*2}
 
 
% 'Name#n' pins a reference to the n-th derivation instead of ranging
% over all of them, and the endings become form: the climbing strain
% takes the third ending and stays open on the third, the retrograde
% takes the first and closes on the tonic.
 
Climb {Tag#3, Cad, Beat*2}
Retro {Tag#1, Cad, Beat*2}
 
 
% Eighteen measures, and nothing in them written twice: three strains
% out of one Tune, three endings out of one Tag, one Beat under every
% measure.
 
Verse {Tag#2, Cad, Beat*2}
Climb {Tag#3, Cad, Beat*2}
Retro {Tag#1, Cad, Beat*2}

% A grammar line NAMES material with '::=', and every uppercase token is
% a REFERENCE that expands to the named material inline. Nothing here is
% written twice: Tune names the four-bar melody, Walk the bass under it,
% Beat one measure of the groove, and Verse superposes all three. Naming
% sounds nothing by itself — the last line STATES Verse, and that plays.

bpm 75
meter 4
unit 1/4
key g4 harm

Tune ::= | 1 2 3 4 |
         | 5 _2 4 3 |
         | 6 5 4 3 |
         | 2 _3 .7 |
Walk ::= | .1 _2 .5 .1 |
         | .4 _2 .1 .4 |
         | .5 _2 .2 .5 |
         | .1 _2 .4 .5 |
Beat ::= | kick hat snare hat kick kick snare hat |

assert Beat*4 == Beat Beat Beat Beat

Verse ::= {Tune, Walk, Beat*4}

Verse

% Marks after a reference cover the WHOLE expansion, so one rule states
% several passages. Climb is those same four bars two scale steps up —
% the key decides where the half steps land — and Retro is those bars
% backwards, durations kept, so the melody opens on the leading tone and
% lands on the tonic:

Climb ::= {Tune@~2, Walk@~2, Beat*4}
Retro ::= {Tune~, Walk, Beat*4}

Climb
Retro

% '=' separates ALTERNATIVES: one name, three bodies. Tag is how the
% phrase ends over the cadence bass — closed on the tonic, open on the
% fifth, soft on the third. 'enum' lists each distinct derivation with
% its own ▶, and a plain reference takes the first, which the assert
% below states in the language:

Tag ::= | 2 _2 .7 2 | 1 _4 |
      = | 2 _2 .7 2 | 5 _4 |
      = | 4 _2 3 2 | 3 _4 |
Cad ::= | .5 _2 .2 .5 | .1 _4 |

enum Tag
assert Tag == Tag#1

Verse {Tag, Cad, Beat*2}

% 'Name#n' pins a reference to the n-th derivation instead of ranging
% over all of them, and the endings become form: the climbing strain
% takes the third ending and stays open on the third, the retrograde
% takes the first and closes on the tonic.

Climb {Tag#3, Cad, Beat*2}
Retro {Tag#1, Cad, Beat*2}

% Eighteen measures, and nothing in them written twice: three strains
% out of one Tune, three endings out of one Tag, one Beat under every
% measure.

Verse {Tag#2, Cad, Beat*2}
Climb {Tag#3, Cad, Beat*2}
Retro {Tag#1, Cad, Beat*2}

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

Opening…

Using grammars · Pattern Engine