Comments on: let 5 = 6

By: Georg

Georg — Sun, 04 Oct 2009 13:15:14 +0000

Now, if I do

let Just a = Nothing

why does GHCI tell me that “a” is of type GHC.Prim.Any?

By: JadeNB

JadeNB — Sat, 03 Oct 2009 03:43:47 +0000

@Matt R: Because Haskell is lazy! See this Reddit comment for a nice discussion. For me, this became much clearer when translated into lambda-notation (as I said on this other Reddit comment): It's much clearer to me what's happening when I change let 5 = 6 in f 5 to (5 -> f 5) 6—there's a non-exhaustive pattern match crying out for attention! (Have I translated it incorrectly?)

By: Matt R

Matt R — Fri, 02 Oct 2009 15:47:05 +0000

How come “let 5 = 6″ doesn’t throw a “Irrefutable pattern” exception?

By: Martijn

Martijn — Fri, 02 Oct 2009 13:39:42 +0000

@lilac There’s also more to be said about !’s dual, the ~.

By: Martijn

Martijn — Fri, 02 Oct 2009 13:25:00 +0000

@gracjan Thanks! I’m glad you like it. And no, I don’t mind at all. Thanks for linking back.

By: Martijn

Martijn — Fri, 02 Oct 2009 13:24:50 +0000

@lilac Thanks! Those are pretty neat.

By: gracjan

gracjan — Fri, 02 Oct 2009 12:48:07 +0000

I find your post to be the best introduction to pattern matching ever! Just translated to Polish word for word on my blog here: http://gracjanpolak.wordpress.com/2009/10/02/let-5-6/. I hope you don’t mind (link back is inside).

By: let 5 = 6 « Haskell. Po polsku.

let 5 = 6 « Haskell. Po polsku. — Fri, 02 Oct 2009 12:45:15 +0000

[...] let 5 = 6 By gracjanpolak Tłumaczone z let 5 = 6 by Martijn van Steenbergen: [...]

By: Linktipps #14 :: Blackflash

Linktipps #14 :: Blackflash — Fri, 02 Oct 2009 11:42:08 +0000

[...] [...]

By: lilac

lilac — Fri, 02 Oct 2009 10:35:41 +0000

Two more cases to consider (with subtly different semantics):

let !5 = 6
5 <- return 6