import edu.neu.ccs.demeter.dj.*;
import java.util.*; 

Exps = 
  <exps> CommaList(Exp) 
  [*l "equations" <eqs> CommaList(Equation)].
Exp : Simple | Compound | QuantifierCompound.
Simple : Forward | Backward | 
	 Sequential | Later | UpOverDown .
Forward = 
  "->" <source> ClassName 
  ["edge" EdgeName] [<steps> Steps] 
  <target> ClassName.
Backward = 
  "<-" <source> ClassName 
  ["edge" EdgeName] [<steps> Steps] 
  <target> ClassName.
Sequential = "seq" <source> ClassName CommaList(ClassName).
Later = 
  "->X<-" <source> ClassName 
  ["edge" EdgeName] [<steps> Steps] 
  <target> ClassName.
UpOverDown = 
  "=>X<=" <source> ClassName 
  ["edge" EdgeName] [<steps> Steps] 
  <target> ClassName.
Exists = "exists" CommaList(ClassName) *l Exp.

Steps: Unlimited | Limited.
// if steps is absent, the default meaning is unlimited
Unlimited = "*".
Limited = <i> Integer.

Compound = Op <args> CommaList(Exp).
Op : Join | Union.
Join = "join".
Union = "union".

QuantifierCompound : Exists.

Equation = *l <left> Exp "=" *l <right> Exp.
ClassName = Ident.
EdgeName = Ident.

CommaList(S) ~ "(" *l + S {"," *l S *s} - *l ")" .

Main = <s> String.