On Feb 13, 2008 5:36 AM, Luke Palmer <[EMAIL PROTECTED]> wrote:
> On Feb 13, 2008 9:33 AM, <[EMAIL PROTECTED]> wrote:
> > The approach is based on the final tagless representation. Here is our
> > DSL:
> >
> > > class Exp repr where
> > > constant :: Int -> repr Int
> > > variable :: String -> repr Int
> > > add :: repr Int -> repr Int -> repr Int
> > > sub :: repr Int -> repr Int -> repr Int
>
> This is very nice. May I ask, though, what is the purpose of all the
> Ints appearing as arguments to repr here? Looking over this code, it
> seems that it would work just as well if they were all omitted.
In this example, they could be omitted. But let's say you had a
language more than one type:
class Exp repr where
constant :: Int -> repr Int
variable :: String -> repr Int
add :: repr Int -> repr Int -> repr Int
sub :: repr Int -> repr Int -> repr Int
true :: repr Bool
false :: repr Bool
and :: repr Bool -> repr Bool -> repr Bool
less_than :: repr Int -> repr Int -> repr Bool
if_ :: repr Bool -> repr a -> repr a -> repr a
The argument to repr prevents you from writing ill-typed code like
"if_ (variable "x") (constant 0) false".
--
Dave Menendez <[EMAIL PROTECTED]>
<http://www.eyrie.org/~zednenem/>
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