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  1. 17 Apr, 2013 1 commit
  2. 07 Apr, 2013 2 commits
    • Andrei Paskevich's avatar
      whyml: drop read effects · 9fd9469c
      Andrei Paskevich authored
      Now that ghost writes are checked via e_syms.syms_pv,
      there is no use for read effects anymore.
      9fd9469c
    • Andrei Paskevich's avatar
      whyml: reimplement verification of the ghost writes · 30c225b4
      Andrei Paskevich authored
      This fixes one bug and several deficiencies in the previous
      implementation, which was based on read effects. One caveat
      about the current version is that we treat all type variables
      in a polymorphic type as visible (= non-ghost) even if they
      only occur in the ghost fields. For example, the following
      code is rejected:
      
        type strange 'a = { ghost contents : 'a }
      
        let test () =
          let x = { contents = ref 0 } in
          x.contents := 42
      
      Even though the field [contents] is ghost and cannot be reached
      from the real-world code, the type of x is [strange (ref int)]
      and the region of the reference is considered to be visible.
      Thus the last assignment is seen as an illicit ghost write.
      
      On the other hand,
      
        type strange 'a = { ghost contents : ref 'a }
      
      and
      
        type strange 'a = { ghost mutable contents : 'a }
      
      permit ghost writes into [contents] without problem.
      Ghost writes into ghost variables are also okay.
      30c225b4
  3. 06 Apr, 2013 1 commit
    • Andrei Paskevich's avatar
      whyml: keep track of pvsymbols and psymbols in expressions · dce120fa
      Andrei Paskevich authored
      this commit changes the way of tracking occurrences of regions
      and type variables for the purposes of generalization, effect
      filtering, and effect checks. It restricts the previous
      implementation in two aspects:
      
      - a psymbol p can be monomorphic (= non-generalizable) in an effect
        only if p depends (= is defined via) a pvsymbol whose type contains
        the affected region. See bench/programs/bad-typing/recfun.mlw
        for an example. This restriction is required for soundness.
      
      - an argument of a psymbol cannot contain a region shared with
        another argument or an external pvsymbol. However, we do not
        require (so far) that the argument's type doesn't contain the same
        region twice and we allow the result type to contain known regions.
        This restriction is not necessary for soundness, and is introduced
        only to avoid some unintentional user errors and reduce the gap
        between the types that can be implemented in a "let" and the types
        that can be declared in a "val".
      dce120fa
  4. 27 Mar, 2013 1 commit
  5. 06 Mar, 2013 1 commit
  6. 03 Mar, 2013 1 commit
    • Andrei Paskevich's avatar
      track dangerous applications of equality · bb6734a1
      Andrei Paskevich authored
      In programs, but also in pure theories, it is not safe to compare
      arbitrary types. For example, if we have a record with ghost fields,
      a comparison may produce different results before and after ghost
      code elimination. Even for pure types like 'map' or 'set', it is
      unlikely that the result of logical equality will be the same as
      the result of OCaml structural equality on the implemented type.
      
      This commit makes the first step towards fixing this issue.
      We proceed in the following way:
      
      1. Every lsymbol (pure function or predicate symbol) carries
         a subset of type variables of its signature, called "opaque
         type variables". By marking a type variable 'a opaque in an
         lsymbol's signature, the user guarantees that this lsymbol
         can be implemented without ever comparing values of type 'a.
         In other words, this is a promise not to break into a type
         variable.
      
         The corresponding syntax is: "predicate safe (x y : ~'a)".
      
         All type variables in undefined symbols are non-opaque,
         unless annotated otherwise. Non-opaque is the default
         to keep the change conservative.
      
         Opacity of type variables in defined symbols is inferred
         from the definition. If the definition violates a given
         opacity annotation, an exception is raised. Notice that
         we only check definitions in _theory_ declarations. One
         can define an lsymbol in a _task_ in a way that violates
         opacity. We cannot forbid it, because various elimination
         transformations would replace safe operations (such as
         matching) with equalities. This is not a problem, since in
         the pure logical realm of provers opacity is not required
         One exception would be Coq, whose transformation chain must
         never perform such operations.
      
         All type variables in inductive predicates are non-opaque.
         Indeed, we can redefine equality via an inductive predicate.
         [TODO: find safe forms of inductive definitions and implement
         more reasonable restrictions.]
      
         All type variables in constructors and field symbols are opaque.
      
         It is forbidden to instantiate an opacity-preserving symbol
         with an opacity-breaking one in a clone substitution.
      
      2. Similar type variable tracking is implemented for program symbols.
         Type variables in the signature of a "val" are non-opaque unless
         annotated otherwise. Opacity of type variables in defined symbols
         is inferred from the definition, and an exception is raised, if
         a given annotation is violated.
      
         The internal mechanism of tracking is different: the "eff_compar"
         field in effects contains the type variables that occur under
         equality or any other opacity-breaking operation. In this respect,
         our API is inconsistent between lsymbols and psymbols: the former
         asks for the opaque tvsymbols, the latter requires us to fill the
         spec with "comparison effects" for the non-opaque ones. [TODO:
         add the "~opaque" argument to create_psymbol and make the WhyML
         core fill the effect under the hood.]
      
         Every time an lsymbol or a psymbol is applied in a program,
         we check the substitution into its signature's type variables.
         If a non-opaque type variable is instantiated with a program type,
         an exception is raised. [TODO: be more precise and reject only
         types with ghost and model components - being mutable, private,
         or carrying an invariant doesn't conflict with equality.]
      
         Notice that we do not allow to compare program types even in
         the ghost code. This is not needed if we only consider the
         problems of the code extraction, but _might_ be necessary,
         if we also want to protect Coq realisations (see below).
      
      This commit fixes the immediate problem of breaking the ghost
      guarantees when equality or some other opacity-breaking lsymbol
      is applied in a program to a type with ghost or "model" parts.
      
      This leaves the problem of code extraction for programs that
      compare complex types such as maps or sets (Coq driver is
      affected by this, too, I guess). The next step is to provide
      annotations for problematic type constructors. A declaration
      "type ~map 'a 'b" would mean "logical equality on this type
      is likely to be different from the structural equality on any
      implementation of this type - therefore do not apply equality
      to it: neither in programs (because this can't be implemented),
      nor in pure functions (because they are extracted, too, and
      because this can't be realized with Leibniz equality in Coq)."
      [TODO: discuss and implement.]
      
      [TODO: mb choose better term for "opaque" and notation for ~'a.]
      bb6734a1
  7. 07 Feb, 2013 1 commit
  8. 03 Feb, 2013 4 commits
  9. 05 Jan, 2013 2 commits
  10. 19 Dec, 2012 1 commit
  11. 13 Nov, 2012 2 commits
  12. 21 Oct, 2012 1 commit
  13. 20 Oct, 2012 1 commit
    • Andrei Paskevich's avatar
      simplify copyright headers · 11598d2b
      Andrei Paskevich authored
      + create AUTHORS file
      + fix the linking exception in LICENSE
      + update the "About" in IDE
      + remove the trailing whitespace
      + inflate my scores at Ohloh
      11598d2b
  14. 17 Oct, 2012 1 commit
    • Andrei Paskevich's avatar
      move whyml to the Why3 library · 4599fe6b
      Andrei Paskevich authored
      + do not build src/programs/
      + build the library in lib/why3/
      + fix use_api.ml for the case when Alt-Ergo is not present
      + distribute lib/coq/BuiltIn.v
      + rename src/config to src/why3config
      + rename src/bench to src/why3bench
      + move src/config.ml to src/util/
      4599fe6b
  15. 02 Oct, 2012 1 commit
  16. 22 Sep, 2012 3 commits
  17. 17 Sep, 2012 1 commit
  18. 11 Sep, 2012 1 commit
  19. 04 Aug, 2012 2 commits
  20. 03 Aug, 2012 2 commits
    • François Bobot's avatar
      Documentation: add description to all the registration functions · 29201f7c
      François Bobot authored
       (metas, debug flags, transformations, formats) except for label.
      
      This description is used in --list-*. The description can use any of
      the formatting markup of Format "@ " "@[",...
      
      Transformations can also specify from which metas and labels they
      depend, and add informations about how they are interpreted.
      
      TODO:
        - complete and correct the documentation
        - when a transformation use Trans.on_meta, it should be possible to
          add an interpretation of the metas in the documentation.
        - recover a summary version of --list-* ?
        - be able to export in latex?
      29201f7c
    • Andrei Paskevich's avatar
      c765e595
  21. 28 Jul, 2012 1 commit
  22. 16 Jul, 2012 1 commit
    • Andrei Paskevich's avatar
      whyml: several API simplifications · 9b75e276
      Andrei Paskevich authored
      - get rid of val_decl, the psymbol/pvsymbol is enough
      - get rid of vtv_vars, keep the varset in pvsymbol
      - include fresh regions in pd_news (will serve for clone)
      9b75e276
  23. 14 Jul, 2012 3 commits
  24. 12 Jul, 2012 2 commits
  25. 11 Jul, 2012 1 commit
  26. 07 Jul, 2012 1 commit
  27. 06 Jul, 2012 1 commit