Hello, Haskell!
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Changed directory: /home/hugo/Academic/Teaching/_Atual/TCPF/Aulas/
Aula22.hs:7:13: error: …
    * Found hole: _ :: Foo
    * In an equation for `f': f "oi" = _
    * Relevant bindings include
        f :: String -> Foo
          (bound at /home/hugo/Academic/Teaching/_Atual/TCPF/Aulas/Aula22.hs:7:1)
      Valid hole fits include
        Hugo :: Foo
          (defined at /home/hugo/Academic/Teaching/_Atual/TCPF/Aulas/Aula22.hs:3:12)
        Matheus :: Foo
          (defined at /home/hugo/Academic/Teaching/_Atual/TCPF/Aulas/Aula22.hs:3:19)
  |
Compilation failed.
λ>