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by lmm 229 days ago
> I have to wonder if programming should have kept pascals distinction between functions that only return one thing and procedures that go off and manipulate other things and do not give a return value.

What you want is to use a language that has higher-kinded types and monads so that functions can have both effects (even multiple distinct kinds of effects) and return values, but the distinction between the two is clear, and when composing effectful functions you have to be explicit about how they compose. (You can still say "run these three possibly-erroring functions in a pipeline and return either the successful result or an error from whichever one failed", but you have to make a deliberate choice to).
1 comments
Warwolt 229 days ago
Making a distinction between pure and effectful functions doesnt require any kind of effect system though.

Having a language where "func" defines a pure function and "proc" defines a procedure that can performed arbitrary side effects (as in any imperative language really) would still be really useful, I think

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lmm 229 days ago
> Having a language where "func" defines a pure function and "proc" defines a procedure that can performed arbitrary side effects (as in any imperative language really) would still be really useful, I think

Rust tried that in the early days, the problem is no-one can agree on exactly what side effects make a function non-pure. You pay almost all the costs of a full effect system (and even have to add an extra language keyword) but get only some of the benefits.

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cestith 228 days ago
The definition I’ve used for my own projects is that anything that touches anything outside the function or in any way outlives the function is impure. It works pretty well for me. That is, no i/o, mutability of a function-local variable is okay but no touching other memory state (and that variable cannot outlive the return), the same function on the same input always produces the same output, and there’s no calling of impure code from within pure code. Notice this makes closures and currying impure unless done explicitly during function instantiation, making those things at least nominally part of the input syntactically. YMMV.
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stOneskull 228 days ago
nim does that. and they are called that.
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