Re: [Haskell-beginners] University project - weird problem

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] mailto:mutilating.cauliflowers.stephen@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 " \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 " \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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