[Haskell-beginners] Data.Text to Int?

[Emmanuel Touzery]

good pattern matching, combining both the Right and the pair matching.. I
didn't realize I can do both at once :-)

I'll use this, thank you!

Emmanuel


On Fri, Dec 14, 2012 at 6:25 PM, Daniel Fischer <
daniel.is.fischer at googlemail.com> wrote:

> On Freitag, 14. Dezember 2012, 16:19:02, Emmanuel Touzery wrote:
> > I see... However it uses Either and returns a pair, unlike "read". It's
> > a plus for reliability but an annoyance in my case. In my case I know
> > positively it's a number.
> > In this case I did a filter isDigit, but this will happen also if I
> > match using a regular expression and [0-9] or \d.
> >
> > In the end the most terse way to code it is to go through unpack then it
> > seems.
> > Using Data.Text.Read all I see is:
> >
> > fst $ right $ decimal t
> > where right (Right a) = a
> >
> > so I'll probably do:
> >
> > read $ unpack t
> >
> > and be done with it...
>
> Note that unpacking to String and then reading from the String is not the
> most
> efficient way.
>
> For the cases you are sure to have a valid input Text and no leftovers (you
> are interested in), you can define
>
> it'sSafeIPromise :: Reader a -> Text -> a
> it'sSafeIPromise = (value .)
>   where
>     value (Right (v,_)) = v
>
> and use
>
> readInt :: Text -> Int
> readInt = it'sSafeIPromise decimal
>
> If you use it a lot, it's worth the bit of additional typing.
>
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