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Numeral and Command Parameters

• Example:
  • const K=2; var A; newint;
    proc P(M: comm) = A:=K+1; M;
    proc Q(X: int) = A:=X
    in call P(call Q(2));
    call P(call P(call Q(K)));
    call P(A:=K)
• Command parameters evaluated lazily.
• Eagerly evaluated command parameters:
  • Argument defines backtracking point.
  • [[pi |-call I(C): comme s
       = p([[pi |- C: comm]]e s)s
       where (I=p) in e
  • var A; newint;
    proc P(M: comm) =
       ...if error then M else ...fi
    in ...call P(A:=0)
  • Reference of M extracts old store!