// class dictionary
Patchwork = 
  "primitives" <primitives> List(PrimitiveExp) 
  "description" <pattern> PatchworkExp [A].
PatchworkExp : 
  PrimitiveExp | TurnExp | SewExp 
    *common* ["length" <length> Measure] ["width" <width> Measure].
PrimitiveExp = "primitive" <patternName> Name.
TurnExp = "(turn" <arg1> PatchworkExp ")".
SewExp  = "(sew" <arg1> PatchworkExp <arg2> PatchworkExp ")".
List(S) ~ {S}.
Measure = <v> DemNumber.
Name = <v> DemIdent.
A= "a" [B].
B:A *common* C.
C=.
D:C *common* E. 
E = .