Basic question about writing effects in terms of other effects

[sullyj3]

My question is, must the "higher level" effect always be dynamically dispatched?

To make it concrete, suppose I wanted to write an effect Hello with a single nullary operation hello which dumps a text file containing "hello world". If I want to implement this in terms of FileSystem, which is statically dispatched, must Hello be dynamically dispatched? (I'm hazy on the details of how to do that actually, I think you use reinterpret?). It feels like it ought to be able to be static, since the implementation never changes.

[arybczak]

My question is, must the "higher level" effect always be dynamically dispatched?

Yes. If you want to depend on an existing effect, it has to be dynamically dispatched. Static effects are primitive in a sense as they can't use other effects.

But considering that the FileSystem effect itself is static and just a thin wrapper for stuff from base/bytestring, you can just make hello use hPutStrLn (or writeFile) directly.

[sullyj3]

Ok, thanks. Yeah, Hello/FileSystem was just an example, in the actual case I'm interested in the lower level effect has a bunch of functionality I don't want to reimplement. I'll just make the higher level one dynamic.