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Comment by programmer_dude | Hacker News Reader

The distinction in ALGOL, Pascal etc. is useless.

But if you change your definitions such that expressions always evaluate to a single value and do not have any side effects while statements produce some kind of side effect (and may or may not yield a value), the distinction becomes important.

Especially if you believe side-effects need special handling (i.e. you are a functional programmer).

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It's been done in some Pascal descendants: functions were required to be pure but procedures were allowed to mutate global state. Some even went as far as to remove functions altogether (with quite unpalatable results).

The only popular language I can think of that requires side effects to be declared is Haskell. Which doesn't have a distinction between statements and expressions.

Are there any good examples of languages that have it, where it isn't "useless"?

python, javascript, pretty much any language that is popular. I believe everything in Haskell is an expression, even the do notation, no?

But I think the argument being advanced is that the distinction between statements and expressions is fundamentally unnecessary. I don’t really know of any good argument in favour of them: I tend to think lisps have the perfect and simplest possible syntax.

Yes, that is indeed the point I was making. And yes, I’m a lisp programmer.

Python, Lisp and Javascript don't require functions with side effects to be declared in a particular way. Haskell does.

The question was about expressions vs statements, not about the IO type.

I was replying to the point programmer_dude made in his comment.

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