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[Frama-c-discuss] Problem with predicate and location labels

  • Subject: [Frama-c-discuss] Problem with predicate and location labels
  • From: hollas at (Boris Hollas)
  • Date: Wed, 16 Feb 2011 17:49:10 +0100 (CET)

Hello Virgile,

so, if ACSL predicates are evaluated by-value, is there a way to define a
predicate that has the same behavior as

#define unchanged(k) (k <==> \old(k))

that can be used in other contracts?

Alternatively, I may use assigns L instead and make sure that k is not in
L. But there's a problem if the function contains an if-statement and
assigns k in one branch, but not in the other. Since assigns is a keyword
like requires or ensures, I can't specify a postcondition such as

ensures (cond ==> assigns k) && (!cond ==> assigns \empty);

It is possible using behaviors but these can't be specified as predicates
to be reused in other contracts.

BTW, I believe the ACSL manual, sections 2.3.3, 2.3.4 is wrong on the
equivalence of named and regular contract as stated on p. 30.