Comment by __s

Haskell interfaces with the real world. ST allows for mutability in pure context

https://github.com/serprex/Fractaler/blob/master/Fractaler.h... fractal renderer I wrote in highschool, has mouse controls for zoom / selecting a variety of fractals

https://github.com/serprex/bfhs/blob/master/bf.hs brainfuck interpreter which mostly executes in pure context, returning stdout with whether program is done or should be reinvoked with character input. Brainfuck tape implemented as zipper

your program may exist in real world, but most of it doesn't care about much of the real world