just now I wrote a message to haskell-pr...@haskell.org to propose a
non-recursive let. Unfortunately, the default let is recursive, so we
only have names like let' for it. I also mentioned the ugly workaround
(<- return $) that I was shocked to see the first time, but use myself
On 10.07.2013 09:34, o...@okmij.org wrote:
The greater evil is that Haskell does not have a non-recursive let.
This is source of many non-termination bugs, including this one here.
let should be non-recursive by default, and for recursion we could have
the good old "let rec".
Hear, hear! In OCaml, I can (and often do) write
let (x,s) = foo 1  in
let (y,s) = bar x s in
let (z,s) = baz x y s in ...
In Haskell I'll have to uniquely number the s's:
let (x,s1) = foo 1  in
let (y,s2) = bar x s1 in
let (z,s3) = baz x y s2 in ...
and re-number them if I insert a new statement. BASIC comes to mind. I
tried to lobby Simon Peyton-Jones for the non-recursive let a couple
of years ago. He said, write a proposal. It's still being
written... Perhaps you might want to write it now.
In the meanwhile, there is a very ugly workaround:
test = runIdentity $ do
(x,s) <- return $ foo 1 
(y,s) <- return $ bar x s
(z,s) <- return $ baz x y s
After all, bind is non-recursive let.
Andreas Abel <>< Du bist der geliebte Mensch.
Theoretical Computer Science, University of Munich
Oettingenstr. 67, D-80538 Munich, GERMANY
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