[Haskell-cafe] Byte Histogram
Richard O'Keefe
ok at cs.otago.ac.nz
Mon Feb 7 23:05:30 CET 2011
On 8/02/2011, at 10:00 AM, Andrew Coppin wrote:
> I clearly have my languages mixed up.
>
> The language I'm thinking of required all variables (even top-level ones) to be declared with "let" - unless the definition is recursive, in which case you have to say "letrec" (i.e., the compiler it too stupid to deduce this automatically). Apparently that isn't Clean...
That sounds like an ML-family language, possibly OCAML.
However, this is *not* a question of stupidity. It's a question of scope rules.
Example 1:
let f x = 1;;
let f x = if x = 0 then 0 else f x;;
f 3;;
This answers 1.
Example 2:
let f x = 1;;
let rec f x = if x = 0 then 0 else f x;;
f 3;;
This goes into an infinite loop.
If you don't like redeclaration, which is rather useful in an interactive
top level, try nested:
let f x = 1;;
let g y = let f x = if x = 0 then 0 else f x in f (f y);;
vs
let f x = 1;;
let g y = let rec f x = if x = 0 then 0 else f x in f (f y);;
The distinction between let and letrec predates OCAML. Scheme does it too.
More information about the Haskell-Cafe
mailing list