[Haskell-beginners] University project - weird problem

[Stephen Blackheath [to Haskell-Beginners]]

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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