Pattern match on Data.Text constant?-CodePudding

I guess I am blind or something, so that I could not find the idiomatic way to pattern match on Data.Text constants.

Basically, what I want to do is the following:

getTempDriverName dir >>= \case
  "k10temp" -> handleK10Temp dir
  "coretemp.0" -> handleCoreTemp dir
  _ -> fail "Wrong driver"

I want to use Data.Text, since String is lazy and no one knows when the file would be closed. However, apparently the following does not work:

getTempDriverName dir >>= \case
  T.pack "k10temp" -> handleK10Temp dir
  T.pack "coretemp.0" -> handleCoreTemp dir
  _ -> fail "Wrong driver"

Any ideas? What would be the idiomatic way? Of course I could do this:

getTempDriverName dir >>= \case
  name
    | name == T.pack "k10temp" -> handleK10Temp dir
    | name == T.pack "coretemp.0" -> handleCoreTemp dir
    | otherwise -> fail "Wrong driver"

but it involves binding a name I do not care for.

CodePudding user response：

If you really want to pattern match here, you can use the OverloadedStrings extension because Text is an instance of IsString. With this extension, strings have type IsString a => a, just like numbers have type Num a => a:

λ> :set -XOverloadedStrings
λ> :t "hello"
"hello" :: IsString a => a
λ> "sample" :: Text
"sample"

In code:

-- put this pragma at the top of the file
{-# LANGUAGE OverloadedStrings #-}

getTempDriverName dir >>= \case
  "k10temp" -> handleK10Temp dir
  "coretemp.0" -> handleCoreTemp dir
  _ -> fail "Wrong driver"