Bash is just a Monad

haskellrescue.blogspot.com

6 pointsnullzzz2 comments

No, bash is not a monad. Really. This sort of article tends to obscure more than it illuminates.

Bash runs the commands of a pipeline in parallel, so you don't get the sequencing of side-effects that monads provide. You'd better off saying that shell commands are plain functions (mapping stdin to stdout) than insisting they're Kleisli arrows.

But to play along with the conceit: the pipe operator would translate into the >=> operator, not >>=. The first command in the pipeline has a stdin, it's just that usually the first command in a pipeline is one that ignores its stdin.

First, I'd like to say that my intention in this posting was just to give a rough analogy that would make monads a bit less scary for the non-haskellers. I should have stated that more clearly though.

Hoever, I stand corrected. Bash executes the commands in a very different way from the IO monad. Using pure functions like String -> String you'd get the similar effect in Haskell, just like you suggested.

That that would of course disable all side-effects from the "links in the chain". Which is in many cases desired, but that's not Bash though.

I guess I'd need to define a whole new Monad to emulate the way Bash operates. I'm not saying you should emulate it though.

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