EquationSystem = <eqs> List(Equation).
Equation =
  <var> Variable "="
  <exp> Exp "." .
Exp : 
  FunctionCall |
  Variable |
  Numbe.
FunctionCall = "call" <fn> Function
  <args> CommaList(Exp) .
Variable = <variableName> Ident.
Function = <functionName> Ident.
Numbe = <n> Integer.
List(S) ~ {S}.
CommaList(S) ~ "(" S {"," S} ")".

Main = .

// visitors

V1 = <e> EquationSystem <c> Integer.
V2 =  Equation  Variable.