[Haskell-cafe] why does Data.Text.Lazy.IO.readFile return the internal type Data.Text.Lazy.Internal.Text, when Data.Text.IO.readFile returns plain IO Data.Text.Text?

[Daniel Fischer]

Am Freitag 30 April 2010 22:37:38 schrieb Thomas Hartman:
> *Main> :t Data.Text.IO.readFile
> Data.Text.IO.readFile :: FilePath -> IO T.Text
>
> but
>
> *Main> :t Data.Text.Lazy.IO.readFile
> Data.Text.Lazy.IO.readFile
>
>   :: FilePath -> IO text-0.7.1.0:Data.Text.Lazy.Internal.Text
>

Hmm,

Prelude> :t Data.Text.Lazy.IO.readFile
Data.Text.Lazy.IO.readFile
  :: FilePath -> IO text-0.7.1.0:Data.Text.Lazy.Internal.Text
Prelude> :t Data.Text.IO.readFile
Data.Text.IO.readFile
  :: FilePath -> IO text-0.7.1.0:Data.Text.Internal.Text


> why does the lazy version use the internal type, whereas the strict
> version of Text IO just using plain Data.Text type?

Both are using the type from the corresponding .Internal, because that's 
where the type is defined (note that, as with ByteStrings, the strict and 
lazy types are different, lazy is basically a list of strict).
Now, the interesting question is, why is the one displayed as T.Text?
It must be what you import to your Main, but I don't know how to produce 
that effect.

> and how can I get from internal type to regular type when using
> Data.Text?

Use id :: a -> a 
;)

>
> also the internal type doesn't appear to be reflected in the haddock:
> 
> http://hackage.haskell.org/packages/archive/text/0.7.1.0/doc/html/Data-T
>ext-Lazy-IO.html

Follow the 'Source' link at Data.Text.Lazy.Text, that sends you to
http://hackage.haskell.org/packages/archive/text/0.7.1.0/doc/html/src/Data-
Text-Lazy-Internal.html#Text

>
> ghc-pkg list | grep -i text
>     text-0.7.1.0
>
> thanks for any help!