haskellhaskell-turtle

With haskell's turtle library, how to extract filename as String from FilePath?

When using takeFileName I get a type error:

:t v
print v
:t takeFileName
takeFileName v

v :: FilePath

FilePath "/media/miguel/backup/backups"

takeFileName :: FilePath -> FilePath
Couldn't match type ‘Turtle.FilePath’ with ‘String’
Expected type: IHaskellSysIO.FilePath
  Actual type: Turtle.FilePath
In the first argument of ‘takeFileName’, namely ‘v’
In the expression: takeFileName v

Is it because turtle's FilePath is different from prelude's FilePath ?

Solution

  • Turtle still uses system-filepath which has a customized "FilePath" type you can find here. Many other Haskell libraries would use a filepath library which just defines FilePath as a synonym for a String (type FilePath = String). This is the case here with IHaskell.

    So yes both FilePath types mismatch. Note that you can easily convert Turtle.FilePath into a String using show (because the type has a Show instance). You can also convert it into a Text using fp from the Turtle.Format module.

    system-filepath is actually deprecated. There is an issue about this. Please read: https://github.com/Gabriel439/Haskell-Turtle-Library/issues/54

    Hope it helps.