Dafny is a programming language with built-in specification constructs.
Dafny is a compiled language used for functional testing of functional correctness of programs.
Home page: https://dafny.org/
Questions tagged [dafny]
485 questions
0
votes
1 answer
writing inductive lemmas in dafny
I'd like to prove the following in dafny:
function append(xs: seq) : seq {
if |xs| == 0 then []
else [xs[0]] + append(xs[1..])
}
method test(o:seq, xs: seq, i:int)
requires 0 <= i < |xs|
{
if o == append(xs[..i])
…
JRR
- 6,014
- 6
- 39
- 59
0
votes
1 answer
missing invariant in dafny code involving sequences
I am wondering if there is a reason why dafny is unable to verify my program?
https://rise4fun.com/Dafny/Ip1s
Am I missing some additional invariant?
JRR
- 6,014
- 6
- 39
- 59
0
votes
1 answer
Dafny program can't prove this binary search implementation?
We are trying to write a binary search algorithm using Dafny and it seems that Dafny doesn't prove the correctness of the program.
can someone please assist?
These are the errors we are getting:
On INV: This loop invariant might not be maintained by…
Orr Levy
- 11
- 2
0
votes
1 answer
How can I cast a value into two bytes in Dafny?
I want to convert an integer from 0 to 65355 and for that I need a two byte representation. I'm trying to divide it by 2, 8 times, and sum the powers of 2 when the rest is one, and then cast that integer as a byte but I'm having problems meeting the…
0
votes
2 answers
Missing assembly reference when using class
I have the following code
class clazz
{
constructor {:axiom} () requires true
method su(x: int, y:int) returns (r: int)
{
r := x + y;
}
}
method {:main} Main() {
var c := new clazz();
var s := c.su(2,3);
…
Rui Maranhao
- 23
- 3
0
votes
1 answer
How do I make a fuel annotation for a templated function?
I would like to write Dafny some code with fuel annotations, like the following:
predicate {:fuel 0,0} eq(x: A, y: A)
{
x == y
}
lemma {:fuel eq,1,2} reflexive(x: A)
ensures eq(x, x)
{
}
Unfortunately, I get an error…
tjhance
- 961
- 1
- 7
- 14
0
votes
0 answers
Induction hypothesis and the operator %
In the program https://rise4fun.com/Dafny/tlpls Dafny is not able to infer the induction hypothesis from the recursive call to the lemma.
Moreover, what is more surprising is in MVS, if you change assert by assume, and again by assert, then the…
jiplucap
- 155
- 7
0
votes
0 answers
Dafny installation on openSUSE leap 15.0
I am trying to install dafny on my laptop, which runs openSUSE leap 15.0 as OS. Since there is no openSUSE version on https://github.com/Microsoft/dafny/releases
I hoped that dafny-2.1.1.10209-x64-ubuntu-14.04.zip
might do the trick. But, it did…
PHS
- 1
- 1
0
votes
2 answers
Polymorphism in Dafny
I am trying to do polymorphism in Dafny but I can't make it work. I didn't find any documentation to help me with this. Here is the code: https://rise4fun.com/Dafny/uQ1w
trait Atom {
var Leaf? : bool;
}
class Leaf extends Atom {
constructor()…
Andrici Cezar
- 603
- 1
- 9
- 15
0
votes
1 answer
In Dafny, how can a method of one object modify another object?
This Dafny code fails to compile:
class Inner {
method m1() modifies this {}
}
class Outer {
var inner: Inner
constructor(rvec: Inner) { inner := rvec; }
method m2()
modifies this, this.inner
{
var i := 0;
while i < 3
{
…
Jason Orendorff
- 42,793
- 6
- 62
- 96
0
votes
1 answer
Modifying method parameters
Is it possible to annotate Dafny method parameters as mutable, without them being objects?
My goal is to be able to verify
method testMethod(a:int, b:int) returns (res :int) {
res :=0;
a := (a - b);
assert a < (a-b);
}
Ignoring the fact this…
Daniel Goldberg
- 19,908
- 4
- 21
- 29
0
votes
0 answers
Unstable long calculations
Trying to use Dafny as a CAS to check that some algebraic calculations are correct.
Dafny does a good job, except that it gets unstable for longer ones, failing to verify some very easy steps even when spoon-fed.
calc == {
// a dozen lines...
k…
Valéry
- 4,574
- 1
- 14
- 25
0
votes
1 answer
Dafny export clause in a module
module A {
export S reveals f
export M provides g
function f (x:int):int
{x+1}
function g (x:int):int
{x-1}
}
module B {
import opened A`{S,M}
//export K reveals k
//export K provides k
function k…
jiplucap
- 155
- 7
0
votes
1 answer
Dafny selection sort descending
I have the following method for performing selection sort in descending order. However, the very first invariant in the while loop is said to be not maintained by the loop, why is that the case?
method sortDesc (a : array)
modifies…
Sreten Jocić
- 165
- 1
- 14
0
votes
1 answer
Using :| in functional code -- recursion on sets
How might one recurse over a set, S, in Dafny when writing pure functional code? I can use :| in imperative code, having checked for non-emptiness, to select an element, s, then recurse on S - {s}. Not quite sure how to make :| deterministic and use…
Kevin S
- 497
- 2
- 10