@inverse

[Xinok via Digitalmars-d]

On Wednesday, 25 February 2015 at 21:25:49 UTC, Daniel N wrote:
> Just throwing an idea out there... How about using annotations 
> to teach the compiler which functions are inverses of 
> each-other, in order to facilitate optimizing away certain 
> redundant operations even if they are located inside a 
> library(i.e. no source).
>
> A little pseudo-code for illustrational purposes, in case my 
> above text is incomprehensible:
>
> void inc() pure nothrow @inverse(dec)
> void dec() pure nothrow @inverse(inc)
>
> void swap(T)(ref T lhs, ref T rhs) pure nothrow @inverse(swap!T)

I like the idea but feel that it's application is too narrow. I 
prefer features which are more general and offer greater 
flexibility. I believe I've read somewhere that some [functional] 
languages define common patterns and equivalent substitutions for 
optimization purposes.

inc(dec(x)) -> x
dec(inc(x)) -> x
cos(x)^^2 + sin(x)^^2 -> 1