Lessons · Grammars

Grammar syntax

::=, alternatives, grouping, references

% A rule names material with '::=', and every UPPERCASE token is a
% REFERENCE that expands where it stands, so a phrase is written once
% and spent many times. Head climbs the tonic triad and walks back
% down; Turn answers it and closes through the raised leading tone.
 
bpm 80
instrument plain
meter 4
unit 1/4
key f# min
 
Head ::= 1 _2 3 _2 5 _2 '1 _2 7 _2 5 _2 4 _2 3 _2
Turn ::= 2 _2 4 _2 3 _2 2 _2 1 _2 .7# _2 1 _4
 
Head Turn Head@~2 Turn
 
 
% '=' separates ALTERNATIVES: one name, several bodies, and the rule
% derives each in turn. 'Name#n' pins the n-th, and the assert proves
% which body #1 is. Three ways to end the same
% phrase, one rule: a leading-tone close, a scale run, an open half.
 
Cad ::= 3 _2 2 _2 .7# _4 1 _8
      = 5 _2 4 _2 3 _2 2 _2 1 _8
      = 2 _2 1 _2 .7# _2 .6 _2 .5 _8
 
assert Cad#1 == 3 _2 2 _2 .7# _4 1 _8
 
Head Cad#1 Head@~2 Cad#3 Head Cad#2
 
 
% '( )' GROUPS, and postfix '&' repeats the group during DERIVATION:
% each successive derivation unrolls it once more, so one rule holds
% the vamp at every length ('--reps' caps it; one-or-more is x x&).
% '*' is not repetition but a duration mark: it repeats in TIME, one
% derivation played twice, and the assert says exactly that.
 
Vamp  ::= {1 5 '1 5} _2
Climb ::= (Vamp Vamp@~2)& Vamp@~4 Cad#2
 
assert Vamp*2 == Vamp Vamp
 
Climb#3
 
 
% 'x?' is a TIMED optional: it derives x or a rest of the SAME
% length, so all eight derivations of Kit are one measure long and the
% backbeat never moves. 'x?y' substitutes y at x's length. '?' takes
% the next sound greedily: '(hat?)' fences it off so the rest default
% stands, 'hat?clap' lets it through.
 
Kit  ::= kick - hat - snare - hat (hat?) kick - hat (kick?) snare - hat hat?clap
Bass<bass> ::= .1 _4 .1 _4 .5 _4 .1 _4
 
{Kit#1, Bass, Head}
{Kit#4, Bass, Head@~2}
{Kit#1, Bass, Head}
{Kit#8, Bass, Turn}
 
 
% Quote a terminal that carries meta-characters: a quoted string is
% ONE grammar symbol whatever punctuation sits inside it, so a whole
% polymetric group can ride in a rule as a single symbol. 'inst'
% aliases a symbol to a sound. A lint checks every right side stays
% brace-balanced, so no derivation hands the player a half-open brace.
 
inst tb = ohat
 
Roll  ::= "tb tb tb tb"
Break ::= "{kick tb tb tb, .1 _4}" Roll "{snare tb tb tb, .5 _4}" Roll
 
Break Break@~2
{Break, Head} {Break, Cad#1}
 
 
% References compose: a rule may name rules that name rules, so the
% form is stated once and played once. Verse stacks kit, bass and line
% three measures deep; Piece spells the whole shape: verse, climb,
% break, verse, close.
 
Verse ::= {Kit#1, Bass, Head} {Kit#4, Bass, Head@~2} {Kit#7, Bass, Turn}
Piece ::= Verse Climb#3 Break Break@~2 Verse Cad#1
 
Piece

% A rule names material with '::=', and every UPPERCASE token is a
% REFERENCE that expands where it stands, so a phrase is written once
% and spent many times. Head climbs the tonic triad and walks back
% down; Turn answers it and closes through the raised leading tone.

bpm 80
instrument plain
meter 4
unit 1/4
key f# min

Head ::= 1 _2 3 _2 5 _2 '1 _2 7 _2 5 _2 4 _2 3 _2
Turn ::= 2 _2 4 _2 3 _2 2 _2 1 _2 .7# _2 1 _4

Head Turn Head@~2 Turn

% '=' separates ALTERNATIVES: one name, several bodies, and the rule
% derives each in turn. 'Name#n' pins the n-th, and the assert proves
% which body #1 is. Three ways to end the same
% phrase, one rule: a leading-tone close, a scale run, an open half.

Cad ::= 3 _2 2 _2 .7# _4 1 _8
      = 5 _2 4 _2 3 _2 2 _2 1 _8
      = 2 _2 1 _2 .7# _2 .6 _2 .5 _8

assert Cad#1 == 3 _2 2 _2 .7# _4 1 _8

Head Cad#1 Head@~2 Cad#3 Head Cad#2

% '( )' GROUPS, and postfix '&' repeats the group during DERIVATION:
% each successive derivation unrolls it once more, so one rule holds
% the vamp at every length ('--reps' caps it; one-or-more is x x&).
% '*' is not repetition but a duration mark: it repeats in TIME, one
% derivation played twice, and the assert says exactly that.

Vamp  ::= {1 5 '1 5} _2
Climb ::= (Vamp Vamp@~2)& Vamp@~4 Cad#2

assert Vamp*2 == Vamp Vamp

Climb#3

% 'x?' is a TIMED optional: it derives x or a rest of the SAME
% length, so all eight derivations of Kit are one measure long and the
% backbeat never moves. 'x?y' substitutes y at x's length. '?' takes
% the next sound greedily: '(hat?)' fences it off so the rest default
% stands, 'hat?clap' lets it through.

Kit  ::= kick - hat - snare - hat (hat?) kick - hat (kick?) snare - hat hat?clap
Bass<bass> ::= .1 _4 .1 _4 .5 _4 .1 _4

{Kit#1, Bass, Head}
{Kit#4, Bass, Head@~2}
{Kit#1, Bass, Head}
{Kit#8, Bass, Turn}

% Quote a terminal that carries meta-characters: a quoted string is
% ONE grammar symbol whatever punctuation sits inside it, so a whole
% polymetric group can ride in a rule as a single symbol. 'inst'
% aliases a symbol to a sound. A lint checks every right side stays
% brace-balanced, so no derivation hands the player a half-open brace.

inst tb = ohat

Roll  ::= "tb tb tb tb"
Break ::= "{kick tb tb tb, .1 _4}" Roll "{snare tb tb tb, .5 _4}" Roll

Break Break@~2
{Break, Head} {Break, Cad#1}

% References compose: a rule may name rules that name rules, so the
% form is stated once and played once. Verse stacks kit, bass and line
% three measures deep; Piece spells the whole shape: verse, climb,
% break, verse, close.

Verse ::= {Kit#1, Bass, Head} {Kit#4, Bass, Head@~2} {Kit#7, Bass, Turn}
Piece ::= Verse Climb#3 Break Break@~2 Verse Cad#1

Piece

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

Grammar syntax · Grammars