13. Release Notes¶
13.1. Release Notes for Version 1.2: New Syntax for “Autodereference”¶
Version 1.2 introduces a simplified syntax for reference variables, to
avoid the somehow heavy OCaml syntax using bang character. In short, this
is syntactic sugar summarized in the following table. An example using
this new syntax is in examples/isqrt.mlw
.
autodereference syntax 
desugared to 









Notice that
the
&
marker adds the typing constraint(x: ref ...)
;toplevel
let/val ref
andlet/val &
are allowed;autodereferencing works in logic, but such variables cannot be introduced inside logical terms.
That syntactic sugar is further extended to pattern matching, function parameters, and reference passing, as follows.
autodereference syntax 
desugared to 



let incr (&x: ref int) =
x < x + 1
let f () =
let ref x = 0 in
incr x;
x

let incr (x: ref int) =
x.contents < x.contents + 1
let f () =
let x = ref 0 in
incr x;
x.contents



The type annotation is not required. Letfunctions with such formal parameters also prevent the actual argument from autodereferencing when used in logic. Pure logical symbols cannot be declared with such parameters.
Autodereference suppression does not work in the middle of a relation
chain: in 0 < x :< 17
, x
will be dereferenced even if (:<)
expects a refparameter on the left.
Finally, that syntactic sugar applies to the caller side:
autodereference syntax 
desugared to 

let f () =
let ref x = 0 in
g &x

let f () =
let x = ref 0 in
g x

The &
marker can only be attached to a variable. Works in logic.
Refbinders and &
binders in variable declarations, patterns, and
function parameters do not require importing ref.Ref
. Any example
that does not use references inside data structures can be rewritten by
using refbinders, without importing ref.Ref
.
Explicit use of type symbol ref
, program function ref
, or field
contents
require importing ref.Ref
or why3.Ref.Ref
.
Operations (:=)
and (!)
require importing ref.Ref
.
Operation (:=)
is fully subsumed by direct assignment (<)
.
13.2. Release Notes for Version 1.0: Syntax Changes w.r.t. 0.88¶
The syntax of WhyML programs changed in release 1.0. The following table summarizes the changes.
version 0.88 
version 1.0 










not needed anymore 


















Note also that logical symbols can no longer be used in nonghost code;
in particular, there is no polymorphic equality in programs anymore, so
equality functions must be declared/defined on a pertype basis (already
done for type int
in the standard library). The CHANGES.md
file
describes other potential sources of incompatibility.
Here are a few more semantic changes.
Proving only partial correctness:
In versions 0.xx of Why3, when a program function is recursive but not given a variant, or contains a while loop not given a variant, then it was assumed that the user wants to prove partial correctness only. A warning was issued, recommending to add an extra
diverges
clause to that function’s contract. It was also possible to disable that warning by adding the label"W:diverges:N"
to the function’s name. Version 1.0 of Why3 is more aggressively requiring the user to prove the termination of functions which are not given thediverges
clause, and the previous warning is now an error. The possibility of proving only partial correctness is now given on a more finegrain basis: any expression for which one wants to prove partial correctness only, must by annotated with the attribute[@vc:divergent]
.In other words, if one was using the following structure in Why3 0.xx:
let f "W:diverges:N" <parameters> <contract> = <body>then in 1.0 it should be written as
let f <parameters> <contract> = [@vc:divergent] <body>
Semantics of the any
construct:
The
any
construct in Why3 0.xx was introducing an arbitrary value satisfying the associated postcondition. In some sense, this construct was introducing some form of an axiom stating that such a value exists. In Why3 1.0, it is now mandatory to prove the existence of such a value, and a VC is generated for that purpose.To obtain the effect of the former semantics of the
any
construct, one should use instead a localval
function. In other words, if one was using the following structure in Why3 0.xx:any t ensures { P }then in 1.0 it should be written as
val x:t ensures { P } in x
13.3. Release Notes for Version 0.80: Syntax Changes w.r.t. 0.73¶
The syntax of WhyML programs changed in release 0.80. The following table summarizes the changes.
version 0.73 
version 0.80 







let rec f (x:int) (y:int): t
variant { t } with rel =
{ P }
e
{ Q }
 Exc1 > { R1 }
 Exc2 n > { R2 }

let rec f (x:int) (y:int): t
variant { t with rel }
requires { P }
ensures { Q }
raises { Exc1 > R1
 Exc2 n > R2 }
= e

val f (x:int) (y:int):
{ P }
t
writes a b
{ Q }
 Exc1 > { R1 }
 Exc2 n > { R2 }

val f (x:int) (y:int): t
requires { P }
writes { a, b }
ensures { Q }
raises { Exc1 > R1
 Exc2 n > R2 }



13.4. Summary of Changes w.r.t. Why 2¶
The main new features with respect to Why 2.xx are the following.
Completely redesigned input syntax for logic declarations
new syntax for terms and formulas
enumerated and algebraic data types, pattern matching
recursive definitions of logic functions and predicates, with termination checking
inductive definitions of predicates
declarations are structured in components called “theories”, which can be reused and instantiated
More generic handling of goals and lemmas to prove
concept of proof task
generic concept of task transformation
generic approach for communicating with external provers
Source code organized as a library with a documented API, to allow access to Why3 features programmatically.
GUI with new features with respect to the former GWhy
session save and restore
prover calls in parallel
splitting, and more generally applying task transformations, on demand
ability to edit proofs for interactive provers (Coq only for the moment) on any subtask
Extensible architecture via plugins
users can define new transformations
users can add connections to additional provers