On 17/10/2015 02:09 PM, Orchid Win7 v1 wrote:
> I've been a Haskell programmer for [at least] 10 years, and I've never
> seen *anybody* do this!

In other news:

   let (,) x y = (5, 6)

This is legal. Bizarre, but true!



Suppose you have a 3-argument constructor:

   data Fubar = Three Char Char Char

Now you can write something like

   Three 'J' 'F' 'K'

which creates a Fubar value. But if you write just Three by itself, you 
have a 3-argument function. As you'd expect.

You can create a 3-argument tuple like this:

   (True, "Red", foo)

Weirdly, if you write

   (,,)

this is a 3-argument function that constructs a 3-tuple. (Count the 
commas carefully; notice how a *three* tuple has *two* commas in it!)

This is a fairly obscure language feature; it's mostly useful when you 
want to quickly pass a tupling function as an argument to something:

   zip = zipWith (,)

However, strictly speaking, that means it's legal to write

   (,,) True "Red" foo

which is exactly the same as (True, "Red", foo), but with weirder syntax.

I had no idea that this is also legal *pattern* syntax! I can't imagine 
why the heck you'd ever want to write it this way in a pattern. But it's 
legal. So there.

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