[Haskell-cafe] let vs. where
Arnar Birgisson
arnarbi at gmail.com
Thu Nov 15 19:35:32 EST 2007
On Nov 16, 2007 12:26 AM, Lennart Augustsson <lennart at augustsson.net> wrote:
> On Nov 14, 2007 1:05 AM, Robin Green <greenrd at greenrd.org> wrote:
> >
> > On Tue, 13 Nov 2007 13:51:13 -0800
> > "Dan Piponi" <dpiponi at gmail.com> wrote:
> >
> > > Up until yesterday I had presumed that guards only applied to
> > > functions. But I was poking about in the Random module and discovered
> > > that you can write things like
> > >
> > > a | x > 1 = 1
> > > | x < -1 = -1
> > > | otherwise = x
> > >
> > > where 'a' clearly isn't a function.
> >
> > Isn't it a function taking zero arguments?
>
> No, Haskell functions take exactly one argument.
Depends on who you ask. From [1]:
<quote>
taxRate = 0.06
total cart = subtotal + tax
where
subtotal = sum cart
taxable = filter isTaxable cart
tax = (sum taxable) * taxRate
This example defines two functions, taxRate, which returns a constant
value, and total, which computes the total cost of the list of items
in a shopping cart. (Although the taxRate definition appears to be
defining a variable, it's best to think of it as a constant function,
a function that takes no parameters and always returns the same
value.) The definition of total is quite expressive, and highlights
the intent of the function, by isolating and naming important
sub-expressions in the computation. (total also refers to an isTaxable
function, not presented here.)
</quote>
Technically, all Haskell functions may take exactly one parameter -
but focusing only on semantics, I guess there's really nothing wrong
with considering constants as parameterless functions, is there?
[1]
cheers,
Arnar
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