Hi Luke
Thank you ! I got it :)
Best Regards
Chunye Wang <[email protected]>
________________________________
From: ext Luke Palmer [mailto:[email protected]]
Sent: Tuesday, January 06, 2009 3:44 PM
To: Wang, Chunye (NSN - CN/Beijing)
Cc: [email protected]
Subject: Re: [Haskell-cafe] Can I destructive rebind a local variable in
haskell?
2009/1/6 Wang, Chunye (NSN - CN/Beijing) <[email protected]>
Dear haskeller,
Can I destructive rebind a local variable like this
import System.Directory
test filename = do
is_dir <- doesDirectoryExist filename
let filename = if not is_dir then filename else filename
Nope. The "filename" on the right side of the = is the same as the
"filename" on the left, so you're making an infinite loop, the same way:
let x = x in x
is an infinite loop. However you can make a new name as you are trying,
you just can't reference the old one. e.g.:
let filename = 42
Here would be just fine.
However, for cases like this, it is useful that single quote is a valid
identifier, so you can say:
let filename' = if not is_dir then filename else filename
(read "filename prime")
Luke
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