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// Concrete language syntax for a Dafny extension with refinement.
// Counter example.
// 6/28/2010
class A {
var n : int;
method Init() modifies this;
{ n := 0;}
method Inc() modifies this;
{ n := n + 1;}
method Dec()
modifies this;
requires n > 0;
{ n := n - 1;}
method Test1(p: int) returns (i: int)
{
assume true;
}
method Test2() returns (o: object)
{ o := this; }
}
class B refines A {
var inc : int, dec : int;
replaces n by n == inc - dec;
// transforms n into inc - dec;
refines Init() modifies this;
{ inc := 0; dec := 0;}
refines Inc() modifies this;
{ inc := inc + 1; }
refines Dec()
modifies this;
requires inc > dec;
{ dec := dec + 1; }
refines Test1(p: int) returns (i: int)
{
i := p;
}
}
// Carrol Morgan's calculator
// 7/2/2010 Kuat
class ACalc {
var vals: seq<int>;
method reset()
modifies this;
{
vals := [];
}
method add(x: int)
modifies this;
{
vals := [x] + vals;
}
method mean() returns (m: int)
requires |vals| > 0;
{
m := seqsum(vals)/|vals|;
}
static function method seqsum(x:seq<int>) : int
decreases x;
{
if (x == []) then 0 else x[0] + seqsum(x[1..])
}
}
class CCalc refines ACalc {
var sum: int;
var num: int;
replaces vals by sum == seqsum2(vals) && num == |vals|;
refines reset()
modifies this;
{
sum := 0;
num := 0;
}
refines add(x: int)
modifies this;
{
sum := sum + x;
num := num + 1;
}
refines mean() returns (m: int)
requires num > 0;
{
m := sum/num;
}
static function method seqsum2(x:seq<int>) : int
decreases x;
{
if (x == []) then 0 else x[0] + seqsum2(x[1..])
}
}
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