Changelog for cryptol2.9.0
2.9.0
Language changes

Removed the
Arith
class. Replaced it instead with more specialized numeric classes:Ring
,Integral
,Field
, andRound
.Ring
is the closest analogue to the oldArith
class; it contains thefromInteger
,(+)
,(*)
,()
andnegate
methods.Ring
contains all the base arithmetic types in Cryptol, and lifts pointwise over tuples, sequences and functions, just asArith
did.The new
Integral
class now contains the integer division and modulus methods ((/)
and(%)
), and the sequence indexing, sequence update and shifting operations are generalized overIntegral
. ThetoInteger
operation is also generalized over this class.Integral
contains the bitvector types andInteger
.The new
Field
class contains types representing mathematical fields (or types that are approximately fields). It is currently inhabited by the newRational
type, and theFloat
family of types. It will eventually also contain theReal
type. It has the operationrecip
for reciprocal and(/.)
for field division (not to be confused for(/)
, which is Euclidean integral division).There is also a new
Round
class for types that can sensibly be rounded to integers. This class has the methodsfloor
,ceiling
,trunc
,roundToEven
androundAway
for performing different kinds of integer rounding.Rational
andFloat
inhabitRound
.The type of
(^^)
is modified to be{a, e} (Ring a, Integral e) => a > e > a
. This makes it clear that the semantics are iterated multiplication, which makes sense in any ring.Finally, the
lg2
,(/$)
and(%$)
methods of Arith have had their types specialized so they operate only on bitvectors. 
Added an
Eq
class, and moved the equality operations fromCmp
intoEq
. TheZ
type becomes a member ofEq
but notCmp
. 
Added a base
Rational
type. It is implemented as a pair of integers, quotiented in the usual way. As such, it reduces to the theory of integers and requires no new solver support (beyond nonlinear integer arithmetic).Rational
inhabits the newField
andRound
classes. Rational values can be constructed using theratio
function, or viafromInteger
. 
The
generate
function (and thusx @ i= e
definitions) has had its type specialized so the index type is alwaysInteger
. 
The new typeclasses are arranged into a class hierarchy, and the typechecker will use that information to infer superclass instances from subclasses.

Added a family of base types,
Float e p
, for working with floating point numbers. The parameters control the precision of the numbers, withe
being the number of bits to use in the exponent andp1
being the number of bits to use in the mantissa. TheFloat
family of types may be used through the usual overloaded functionality in Cryptol, and there is a new builtin module calledFloat
, which contains functionality specific to floating point numbers. 
Add a way to write fractional literals in base 2,8,10, and 16. Fractional literals are overloaded, and may be used for different types (currently
Rational
and theFloat
family). Fractional literal in base 2,8,and 16 must be precise, and will be rejected statically if they cannot be represented exactly. Fractional literals in base 10 are rounded to the nearest even representable number. 
Changes to the defaulting algorithm. The new algorithm only applies to constraints arising from literals (i.e.,
Literal
andFLiteral
constraints). The guiding principle is that we now default these to one of the infinite precision typesInteger
orRational
.Literal
constraints are defaulted toInteger
, unless the corresponding type also hasField
constraint, in which case we useRational
. Fractional literal constraints are always defaulted to `Rational.
New features

Document the behavior of lifted selectors.

Added support for symbolic simulation via the
What4
library in addition to the previous method based onSBV
. The What4 symbolic simulator is used when selecting solvers with thew4
prefix, such asw4z3
,w4cvc4
,w4yices
, etc. TheSBV
andWhat4
libraries make different tradeoffs in how they represent formulae. You may find one works better than another for the same problem, even with the same solver. 
More detailed information about the status of various symbols in the output of the
:browse
command (issue #688). 
The
:safe
command will attempt to prove that a given Cryptol term is safe; in other words, that it will not encounter a runtime error for all inputs. Runtime errors arise from things like divisionbyzero, indexoutofbounds situations and explicit calls toerror
orassert
. 
The
:prove
and:sat
commands now incorporate safety predicates by default. In a:sat
call, models will only be found that do not cause runtime errors. For:prove
calls, the safety conditions are added as additional proof goals. The prior behavior (which ignored safety conditions) can be restored using:set ignoresafety = on
. 
Improvements to the
any
prover. It will now shut down external prover processes correctly when one finds a solution. It will also wait for the first successful result to be returned from a prover, instead of failing as soon as one prover fails. 
An experimental
parmap
primitive that applies a function to a sequence of arguments and computes the results in parallel. This operation should be considered experimental and may significantly change or disappear in the future, and could possibly uncover unknown race conditions in the interpreter.
Bug fixes
 Closed issues #346, #444, #614, #617, #636, #660, #662, #663, #664, #667, #670, #702, #711, #712, #716, #723, #725, #731
2.8.0 (September 4, 2019)
New features

Added support for indexing on the lefthand sides of declarations, record field constructors, and record updaters (issue #577). This builds on a new primitive function called
generate
, where the new syntaxx @ i = e
is sugar forx = generate (\i > e)
. 
Added support for element type ascriptions on sequence enumerations. The syntax
[a,b..c:t]
indicates that the elements should be of typet
. 
Added support for wildcards in sequence enumerations. For example, the syntax
[1 .. _] : [3][8]
yields[0x01, 0x02, 0x03]
. It can also be used polymorphically. For example, the most general type of[1 .. _]
is{n, a} (n >= 1, Literal n a, fin n) => [n]a

Changed the syntax of type signatures to allow multiple constraint arrows in type schemas (issue #599). The following are now equivalent:
f : {a} (fin a, a >= 1) => [a] > [a] f : {a} (fin a) => (a >= 1) => [a] > [a]

Added a mechanism for userdefined type constraint operators, and use this to define the new type constraint synonyms (<) and (>) (issues #400, #618).

Added support for primitive type declarations. The prelude now uses this mechanism to declare all of the basic types.

Added support for Haskellstyle "block arguments", reducing the need for parentheses in some cases. For example,
generate (\i > i +1)
can now be writtengenerate \i > i + 1
. 
Improved shadowing errors (part of the fix for issue #569).
Bug fixes
 Closed many issues, including #265, #367, #437, #508, #522, #549, #557, #559, #569, #578, #590, #595, #596, #601, #607, #608, #610, #615, #621, and #636.
2.7.0 (April 30, 2019)
New features

Added syntax for record updates (see #399 for details of implemented and planned features).

Updated the
:browse
command to list module parameters (issue #586). 
Added support for test vector creation (the
:dumptests
command). This feature computes a list of random inputs and outputs for the given expression of function type and saves it to a file. This is useful for generating tests from a trusted Cryptol specification to apply to an implementation written in another language.
Breaking changes

Removed the
[x..]
construct from the language (issue #574). It was shorthand for[x..2^^n1]
for a bit vector of sizen
, which was often not what the user intended. Users should instead write either[x..y]
or[x...]
, to construct a smaller range or a lazy sequence, respectively. 
Renamed the valuelevel
width
function tolength
, and generalized its type (issue #550). It does not behave identically to the typelevelwidth
operator, which led to confusion. The namelength
matches more closely with similar functions in other languages.
Bug fixes

Improved type checking performance of decimal literals.

Improved type checking of
/^
and%^
(issues #581, #582). 
Improved performance of sequence updates with the
update
primitive (issue #579). 
Fixed elapsed time printed by
:prove
and:sat
(issue #572). 
Fixed SMTLib formulas generated for right shifts (issue #566).

Fixed crash when importing nonparameterized modules with the backtick prefix (issue #565).

Improved performance of symbolic execution for
Z n
(issue #554). 
Fixed interpretation of the
satNum
option so finding multiple solutions doesn't run forever (issue #553). 
Improved type checking of the
length
function (issue #548). 
Improved error message when trying to prove properties in parameterized modules (issue #545).

Stopped warning about defaulting at the REPL when
warnDefaulting
is set tofalse
(issue #543). 
Fixed builds on nonx86 architectures (issue #542).

Made browsing of interactivelybound identifiers work better (issue #538).

Fixed a bug that allowed changing the semantics of the
_ # _
pattern and the
and~
operators by creating local definitions of functions that they expand to (issue #568). 
Closed issues #498, #547, #551, #562, and #563.