[Haskell-beginners] University project - weird problem
Stephen Blackheath [to Haskell-Beginners]
mutilating.cauliflowers.stephen at blacksapphire.com
Wed Apr 21 19:59:03 EDT 2010
Renato,
GHC and Hugs both comply with the Haskell 98 standard, so the same
program will work in both if it's written in Haskell 98.
I've never used Hugs so I don't know what your error means. I just
tried loading it into GHC with -Wall on (enable all warnings) and I got
lots of
c.hs:21:0:
Warning: Pattern match(es) are non-exhaustive
In the definition of `le_bloco': Patterns not matched: []
c.hs:32:0:
Warning: Pattern match(es) are non-exhaustive
In the definition of `separador': Patterns not matched: []
...
It looks like you are not handling the end-of-list case. This might be
related to your problems. If you run in GHC with -Wall, and fix all the
warnings, you should find most of your problems go away. (Haskell is
truly wonderful in this way.)
Steve
Renato dos Santos Leal wrote:
> Thank you Stephen!
>
> Yes, I'm using hugs. My teacher told me to use it and he corrects our
> projects using it, the differece between hugs and GHC, is it large?
>
> I don't know if I got what you meant with pure functions, but I'll keep
> studying.
>
> 2010/4/21 Stephen Blackheath [to Haskell-Beginners]
> <mutilating.cauliflowers.stephen at blacksapphire.com
> <mailto:mutilating.cauliflowers.stephen at blacksapphire.com>>
>
> Renato,
>
> All I did was I added type signatures to your code, and it worked.
> It is a very good idea to put type signatures on all top-level
> functions, otherwise you can get confusing errors.
>
> It looks like you are using Hugs - It is much better to use GHC.
> That's what everyone uses now.
>
> Another thing: For a program this size it doesn't matter much, but
> in Haskell we always try to make our functions pure if we can (that
> is, not IO type). Then you get the best advantage out of using Haskell.
>
>
> Steve
>
>
> listO = ['+', '-', '*', '/', '%', '^', '=', '>', '<', '.', '|', '&',
> '!', '~']
> listS = [';', '{', '(', ')', '}', '[', ']', ',']
> listC = ['0','1'..'9']
> listCF = listC ++ ['.']
> listA = listO ++ listS ++ [' ']
> listPC =
> ["auto","double","int","struct","break","else","long","switch","case",
>
> "enum","register","typedef","char","extern","return","union","const",
>
> "float","short","unsigned","continue","for","signed","void","default",
> "goto","sizeof","volatile","do","if","static","while"]
>
> verifica :: IO ()
>
> verifica = do
> putStr ("Favor visualizar o codigo para ver os bugs e erros do
> programa\n")
> putStr ("Digite o nome do arquivo de entrada: ")
> arqent <- getLine
> texto <- readFile arqent
> le_bloco texto
>
> le_bloco :: String -> IO ()
>
> le_bloco (x:xs)
> | x `elem` listO = do operador (x:xs)
> | x `elem` listC = do cnum (x:xs)
> -- | x `elem` listS = do separador (x:xs)
> | x `elem` listS = do{ putStr[x] ; putStr " <separador>\n" }
> | x == '"' = litstr (xs)
> | x /= ' ' = pchave (x:xs) []
> | x == ' ' = le_bloco xs
> | otherwise = do { putStr "Outro\n" ; le_bloco xs }
>
> separador :: String -> IO ()
>
> separador (x:xs)
> | x `elem` listS = do{ putStr [x] ; separador xs}
> | otherwise = do{ putStr " <separador>\n" ; le_bloco xs}
>
> cnum :: String -> IO ()
>
> cnum (x:xs)
> | x `elem` listCF = do{ putChar x ; cnum xs}
> | otherwise = do{ putStr " <cte. numerica>\n" ; le_bloco (x:xs)}
>
> operador :: String -> IO ()
>
> operador (x:xs)
> | x `elem` listO = do{ putChar x ; operador xs}
> | otherwise = do{ putStr " <operador>\n" ; le_bloco (x:xs)}
>
> litstr :: String -> IO ()
>
> litstr (x:xs)
> | x /= '"' = do{ putChar x ; litstr xs}
> | otherwise = do{ putStr " <literal string>\n" ; le_bloco xs}
>
> pchave :: String -> String -> IO ()
>
> pchave (x:xs) ys
> | x `notElem` listA = pchave xs (ys++[x])
> | otherwise = pPCouI (x:xs) ys
>
> pPCouI :: String -> String -> IO ()
>
> pPCouI (x:xs) z
> | membroPC z = do{ putStr (z ++ " <palavra chave>\n") ; le_bloco
> (x:xs)}
> | otherwise = do{putStr z ; putStr " <identificador>\n" ;
> le_bloco (x:xs)}
>
> membroPC :: String -> Bool
>
> membroPC x
> | x `elem` listPC = True
> | otherwise = False
>
>
> Renato dos Santos Leal wrote:
>
> I've got a university project that demands me to do a program
> that receive a .c file and analyze its syntax using haskell.
> There are just a few things that I have to analyze:
> literal strings, identifiers (in the program: identificadores),
> constants (constantes), operators (operadores) and reserverd
> words(palavras reservadas)
>
> There are two major problems in the program:
>
> (1) I've got this guard in le_bloco: | x `elem` listS = do
> separador (x:xs)
> but it doesn't seem to work. Every time I enable it I recieve
> this in execution time (after calling verifica)
>
> ERROR - Cannot find "show" function for:
> *** Expression : verifica
> *** Of type : IO a
>
> So I've made one workaround that prints the separator but stops
> the program...I guess the problem is doing the recursivity
>
> (2) My second problem is: when I have one identifier or keyword
> alone in a line or it's the last element of it it just won't
> print my coment!
> this is the function:
>
> pPCouI (x:xs) z
> | membroPC z = do{ putStr (z ++ " <palavra chave>\n") ;
> le_bloco (x:xs)}
> | otherwise = do{putStr z ; putStr " <identificador>\n" ;
> le_bloco (x:xs)}
>
> *Please help me solving those problems as soon as possible!*
>
> Here is the whole program:
>
> listO = ['+', '-', '*', '/', '%', '^', '=', '>', '<', '.', '|',
> '&', '!', '~']
> listS = [';', '{', '(', ')', '}', '[', ']', ',']
> listC = ['0','1'..'9']
> listCF = listC ++ ['.']
> listA = listO ++ listS ++ [' ']
> listPC =
> ["auto","double","int","struct","break","else","long","switch","case",
>
> "enum","register","typedef","char","extern","return","union","const",
>
> "float","short","unsigned","continue","for","signed","void","default",
> "goto","sizeof","volatile","do","if","static","while"]
>
> verifica = do
> putStr ("Favor visualizar o codigo para ver os bugs e erros
> do programa\n")
> putStr ("Digite o nome do arquivo de entrada: ")
> arqent <- getLine
> texto <- readFile arqent
> le_bloco texto
> le_bloco (x:xs)
> | x `elem` listO = do operador (x:xs)
> | x `elem` listC = do cnum (x:xs)
> -- | x `elem` listS = do separador (x:xs)
> | x `elem` listS = do{ putStr[x] ; putStr " <separador>\n" }
> | x == '"' = litstr (xs)
> | x /= ' ' = pchave (x:xs) []
> | x == ' ' = le_bloco xs
> | otherwise = do { putStr "Outro\n" ; le_bloco xs }
>
> separador (x:xs)
> | x `elem` listS = do{ putStr [x] ; separador xs}
> | otherwise = do{ putStr " <separador>\n" ; le_bloco xs}
> cnum (x:xs)
> | x `elem` listCF = do{ putChar x ; cnum xs}
> | otherwise = do{ putStr " <cte. numerica>\n" ; le_bloco (x:xs)}
> operador (x:xs)
> | x `elem` listO = do{ putChar x ; operador xs}
> | otherwise = do{ putStr " <operador>\n" ; le_bloco (x:xs)}
> litstr (x:xs)
> | x /= '"' = do{ putChar x ; litstr xs}
> | otherwise = do{ putStr " <literal string>\n" ; le_bloco xs}
>
> pchave (x:xs) ys
> | x `notElem` listA = pchave xs (ys++[x])
> | otherwise = pPCouI (x:xs) ys
> pPCouI (x:xs) z
> | membroPC z = do{ putStr (z ++ " <palavra chave>\n") ;
> le_bloco (x:xs)}
> | otherwise = do{putStr z ; putStr " <identificador>\n" ;
> le_bloco (x:xs)}
> membroPC x
> | x `elem` listPC = True
> | otherwise = False
>
> I'm sorry for the bad english, it's been a while since the last
> time i used it =)
> Ah, I'm just starting to learn Haskell, first time i've seen it
> was like a month ago so pretend that I know nothing
>
>
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