digitalmars.D.learn - Compare lambda expressions
Hi all!
Not sure, if this belongs directly to the D language, or it is
rather maths, but:
given to delegate generating functions and a main
auto func1(int arg)
{
bool delegate(int x) dg;
dg = (x) => arg * x;
return dg;
}
auto func2(int arg)
{
bool delegate(int x) dg;
dg = (x) => arg * x * x / x;
return dg;
}
void main()
{
auto dgf1 = func1(4);
writeln(dgf1(2));
auto dgf2 = func2(4);
writeln(dgf2(2));
writeln(dgf1 == dgf2);
}
the last line gives false, either in this form, as well with
.ptr, as well with .funcptr.
The question is, how to say, whether two lambda expressions are
the same?
What if the lambda expressions are predicates? This case would be
more important for me...
I understand, that there is only a little hope to get answer
other then "impossible", even for the constrained case. In such a
case, I have another opportunity:
Say, I define two lambda functions as strings in, say a json
file. I'm going to parse them and build functions out of them.
How to force the input in a unified manner? In such a case, I
could compare the given strings with some weird regular
expression...
So, the question for this case is:
Is there some normalized form of writing a lambda expression? Any
literature would be more then sufficient as an answer...
Many thanks in advance :)
Apr 26 2016
Meta <jared771 gmail.com> There's no way to do this in D. There have been several proposals but nothing implemented as of yet.
Apr 26 2016
On Tuesday, 26 April 2016 at 14:32:59 UTC, Alex wrote:
Hi all!
Not sure, if this belongs directly to the D language, or it is
rather maths, but:
given to delegate generating functions and a main
auto func1(int arg)
{
bool delegate(int x) dg;
dg = (x) => arg * x;
return dg;
}
auto func2(int arg)
{
bool delegate(int x) dg;
dg = (x) => arg * x * x / x;
return dg;
}
void main()
{
auto dgf1 = func1(4);
writeln(dgf1(2));
auto dgf2 = func2(4);
writeln(dgf2(2));
writeln(dgf1 == dgf2);
}
the last line gives false, either in this form, as well with
.ptr, as well with .funcptr.
The question is, how to say, whether two lambda expressions are
the same?
What if the lambda expressions are predicates? This case would
be more important for me...
I understand, that there is only a little hope to get answer
other then "impossible", even for the constrained case. In such
a case, I have another opportunity:
Say, I define two lambda functions as strings in, say a json
file. I'm going to parse them and build functions out of them.
How to force the input in a unified manner? In such a case, I
could compare the given strings with some weird regular
expression...
So, the question for this case is:
Is there some normalized form of writing a lambda expression?
Any literature would be more then sufficient as an answer...
Many thanks in advance :)
IMHO, if you are to parse them from strings then you need a
parser in order to build an abstract tree, a simpler intermediary
language to restrict the possible patterns expressing an idea, an
optimizer to reduce similar expressions to a unique one and then
you way be able to spot that two given expressions share a common
implementation and thus have the same effect but with no garanty
to catch them all. As far as I know it's still a field of
research.
The bulk of the problem doesn't have much to do with D itself
though.
Apr 26 2016
On Wednesday, 27 April 2016 at 06:59:22 UTC, cym13 wrote:On Tuesday, 26 April 2016 at 14:32:59 UTC, Alex wrote: IMHO, if you are to parse them from strings then you need a parser in order to build an abstract tree, a simpler intermediary language to restrict the possible patterns expressing an idea, an optimizer to reduce similar expressions to a unique one and then you way be able to spot that two given expressions share a common implementation and thus have the same effect but with no garanty to catch them all. As far as I know it's still a field of research.Ok! Thanks!The bulk of the problem doesn't have much to do with D itself though.Yes, I see... The working idea from early in the morning is the following: Force this by the structure of the input file itself: E. g. in the json file, make a section, where lambda expressions are defined, then, in sections where they are needed reference them. This would reduce repeated definitions and would obsolete the need for comparison...
Apr 27 2016