[Haskell-cafe] Language simplicity

[Roel van Dijk]

2010/1/14 Evan Laforge <qdunkan at gmail.com>:
> Wow, that's kind of cute:
>
> {-# LANGUAGE UnicodeSyntax #-}
> (＊) = (*)
> (／) = (/)
> 公式 高 中 低 = 高 ＊ 中 ＊ 低 ／ 整數
> 整數 = 123

That code snippet is also perfectly legal Haskell without the
UnicodeSyntax language extension. You use UnicodeSyntax if you want to
write code like this:

{-# LANGUAGE UnicodeSyntax, ScopedTypeVariables #-}
swap ∷ ∀ α β. (α, β) → (β, α)
swap = uncurry $ flip (,)

> Oddly, if I change the order of these definitions I get syntax
> errors.  Very mysterious.  Nice how it knows that ＊ is a symbol,
> but I'm not sure how I'm supposed to name a type.

I was a bit surprised that you could use ＊ as an operator since it is
a punctuation character. Maybe there are some corner cases with
fullwidth characters or with composition of characters.

> Unicode identifiers are fun but this is a good point.  The line has
> to be somewhere, so it might as well be in the historical position
> unless there are widely agreed on benefits to moving it.

I have already crossed that line:

http://hackage.haskell.org/package/base-unicode-symbols
http://hackage.haskell.org/package/containers-unicode-symbols

But I am aware that there is a point beyond which unicode symbols only
make your code harder to understand. So I try to be conservative in my
use of them. Still, there are a lot of useful and acceptable symbols
which are not part of the historic ASCII set: ∈, ≤, ∪, ∧, ¬, ∘ to name
a few.