never executed always true always false

    1 module Main where
    2 
    3 import LI11718
    4 import qualified Tarefa2_2017li1g186 as T2
    5 
    6 import System.Environment
    7 import Text.Read
    8 
    9 main = do
   10     args <- getArgs
   11     case args of
   12         ["valida"] -> do
   13             str <- getContents
   14             let mapa = readMaybe str
   15             case mapa of
   16                 Nothing -> error "mapa inválido"
   17                 Just m -> print $ T2.valida m
   18         ["testes"] -> print $ T2.testesT2
   19         otherwise -> error "RunT2 argumentos inválidos"