Comment by throwaway17_17

I see I’ve been beaten to the punch, but I’ll post my try anyway.

Your comment about IO handled by an external system In response to a comment about the more general concept of a monad is what they are, somewhat abruptly referring to in the above two comments.

The IO monad in Haskell is somewhat ‘magical’ in that it encapsulates a particular monad instance that encodes computational actions which Haskell defers to an external system to execute. Haskell chose to encode this using a monadic structure.

To be a bit more particular:

The Reader monad is the Haskell Monad instance for what can generically be called an ‘environment’ monad. It is the pattern of using monadic structure to encapsulate the idea of a calling context and then taking functions that do not take a Context variable and using the encapsulating Monad to provide the context for usage within that function that needs it.

Based on your streams in the new system I don’t see a monad, mostly because the Reader instance would basically pipe the IO parameter through functions for you and Zig requires explicit passage of the IO (unless you set a global variable as IO but that’s not a monad, that’s just global state) to each function that uses it.

From my perspective Zig’s IO looks to be more akin to a passed effect token outside the type system ‘proper’ that remains compile time checked by special case.