home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
OS/2 Shareware BBS: 10 Tools
/
10-Tools.zip
/
gofer230.zip
/
Progs
/
Gofer
/
Demos
/
Utils
/
lexer.gs
< prev
Wrap
Text File
|
1994-06-23
|
7KB
|
210 lines
-- A simple attempt to provide the facilities of the Haskell Text
-- class for reading values. If you really want to use this, I
-- would suggest combining it with the Text class in a modified
-- version of the prelude.
--
-- Based, not surprisingly, on the definitions in the Haskell report
-- version 1.2:
type ReadS a = String -> [(a,String)]
class Read a where
readsPrec :: Int -> ReadS a
readList :: ReadS [a]
readList = readParen False (\r -> [pr | ("[",s) <- lex r,
pr <- readl s])
where readl s = [([],t) | ("]",t) <- lex s] ++
[(x:xs,u) | (x,t) <- reads s,
(xs,u) <- readl' t]
readl' s = [([],t) | ("]",t) <- lex s] ++
[(x:xs,v) | (",",t) <- lex s,
(x,u) <- reads t,
(xs,v) <- readl' u]
instance Read () where
readsPrec p = readParen False
(\r -> [((),t) | ("(",s) <- lex r,
(")",t) <- lex s ] )
instance Read Char where
readsPrec p = readParen False
(\r -> [(c,t) | ('\'':s,t)<- lex r,
(c,_) <- readLitChar s])
readList = readParen False (\r -> [(l,t) | ('"':s, t) <- lex r,
(l,_) <- readl s ])
where readl ('"':s) = [("",s)]
readl ('\\':'&':s) = readl s
readl s = [(c:cs,u) | (c ,t) <- readLitChar s,
(cs,u) <- readl t ]
instance Read Int where
readsPrec p = readSigned readDec
instance (Read a) => Read [a] where
readsPrec p = readList
instance (Read a, Read b) => Read (a,b) where
readsPrec p = readParen False
(\r -> [((x,y), w) | ("(",s) <- lex r,
(x,t) <- reads s,
(",",u) <- lex t,
(y,v) <- reads u,
(")",w) <- lex v ] )
reads :: (Read a) => ReadS a
reads = readsPrec 0
read :: (Read a) => String -> a
read s = case [x | (x,t) <- reads s, ("","") <- lex t] of
[x] -> x
[] -> error "read{PreludeRead}: no parse"
_ -> error "read{PreludeRead}: ambiguous parse"
readParen :: Bool -> ReadS a -> ReadS a
readParen b g = if b then mandatory else optional
where optional r = g r ++ mandatory r
mandatory r = [(x,u) | ("(",s) <- lex r,
(x,t) <- optional s,
(")",u) <- lex t ]
lex :: ReadS String
lex "" = [("","")]
lex (c:s) | isSpace c = lex (dropWhile isSpace s)
lex ('-':'-':s) = case dropWhile (/= '\n') s of
'\n':t -> lex t
_ -> [] -- unterminated end-of-line
-- comment
lex ('{':'-':s) = lexNest lex s
where
lexNest f ('-':'}':s) = f s
lexNest f ('{':'-':s) = lexNest (lexNest f) s
lexNest f (c:s) = lexNest f s
lexNest _ "" = [] -- unterminated
-- nested comment
lex ('<':'-':s) = [("<-",s)]
lex ('\'':s) = [('\'':ch++"'", t) | (ch,'\'':t) <- lexLitChar s,
ch /= "'" ]
lex ('"':s) = [('"':str, t) | (str,t) <- lexString s]
where
lexString ('"':s) = [("\"",s)]
lexString s = [(ch++str, u)
| (ch,t) <- lexStrItem s,
(str,u) <- lexString t ]
lexStrItem ('\\':'&':s) = [("\\&",s)]
lexStrItem ('\\':c:s) | isSpace c
= [("\\&",t) | '\\':t <- [dropWhile isSpace s]]
lexStrItem s = lexLitChar s
lex (c:s) | isSingle c = [([c],s)]
| isSym1 c = [(c:sym,t) | (sym,t) <- [span isSym s]]
| isAlpha c = [(c:nam,t) | (nam,t) <- [span isIdChar s]]
| isDigit c = [(c:ds++fe,t) | (ds,s) <- [span isDigit s],
(fe,t) <- lexFracExp s ]
| otherwise = [] -- bad character
where
isSingle c = c `elem` ",;()[]{}_"
isSym1 c = c `elem` "-~" || isSym c
isSym c = c `elem` "!@#$%&*+./<=>?\\^|:"
isIdChar c = isAlphanum c || c `elem` "_'"
lexFracExp ('.':s) = [('.':ds++e,u) | (ds,t) <- lexDigits s,
(e,u) <- lexExp t ]
lexFracExp s = [("",s)]
lexExp (e:s) | e `elem` "eE"
= [(e:c:ds,u) | (c:t) <- [s], c `elem` "+-",
(ds,u) <- lexDigits t] ++
[(e:ds,t) | (ds,t) <- lexDigits s]
lexExp s = [("",s)]
lexDigits :: ReadS String
lexDigits = nonnull isDigit
nonnull :: (Char -> Bool) -> ReadS String
nonnull p s = [(cs,t) | (cs@(_:_),t) <- [span p s]]
lexLitChar :: ReadS String
lexLitChar ('\\':s) = [('\\':esc, t) | (esc,t) <- lexEsc s]
where
lexEsc (c:s) | c `elem` "abfnrtv\\\"'" = [([c],s)]
lexEsc ('^':c:s) | c >= '@' && c <= '_' = [(['^',c],s)]
lexEsc s@(d:_) | isDigit d = lexDigits s
lexEsc ('o':s) = [('o':os, t) | (os,t) <- nonnull isOctDigit s]
lexEsc ('x':s) = [('x':xs, t) | (xs,t) <- nonnull isHexDigit s]
lexEsc s@(c:_) | isUpper c
= case [(mne,s') | mne <- "DEL" : asciiTab,
([],s') <- [match mne s] ]
of (pr:_) -> [pr]
[] -> []
lexEsc _ = []
lexLitChar (c:s) = [([c],s)]
lexLitChar "" = []
isOctDigit c = c >= '0' && c <= '7'
isHexDigit c = isDigit c || c >= 'A' && c <= 'F'
|| c >= 'a' && c <= 'f'
match :: (Eq a) => [a] -> [a] -> ([a],[a])
match (x:xs) (y:ys) | x == y = match xs ys
match xs ys = (xs,ys)
asciiTab = ["NUL", "SOH", "STX", "ETX", "EOT", "ENQ", "ACK", "BEL",
"BS", "HT", "LF", "VT", "FF", "CR", "SO", "SI",
"DLE", "DC1", "DC2", "DC3", "DC4", "NAK", "SYN", "ETB",
"CAN", "EM", "SUB", "ESC", "FS", "GS", "RS", "US",
"SP"]
readLitChar :: ReadS Char
readLitChar ('\\':s) = readEsc s
where
readEsc ('a':s) = [('\a',s)]
readEsc ('b':s) = [('\b',s)]
readEsc ('f':s) = [('\f',s)]
readEsc ('n':s) = [('\n',s)]
readEsc ('r':s) = [('\r',s)]
readEsc ('t':s) = [('\t',s)]
readEsc ('v':s) = [('\v',s)]
readEsc ('\\':s) = [('\\',s)]
readEsc ('"':s) = [('"',s)]
readEsc ('\'':s) = [('\'',s)]
readEsc ('^':c:s) | c >= '@' && c <= '_'
= [(chr (ord c - ord '@'), s)]
readEsc s@(d:_) | isDigit d
= [(chr n, t) | (n,t) <- readDec s]
readEsc ('o':s) = [(chr n, t) | (n,t) <- readOct s]
readEsc ('x':s) = [(chr n, t) | (n,t) <- readHex s]
readEsc s@(c:_) | isUpper c
= let table = ('\DEL',"DEL") : zip ['\NUL'..] asciiTab
in case [(c,s') | (c,mne) <- table,
([],s') <- [match mne s]]
of (pr:_) -> [pr]
[] -> []
readEsc _ = []
readLitChar (c:s) = [(c,s)]
readDec, readOct, readHex :: ReadS Int
readDec = readInt 10 isDigit (\d -> ord d - ord '0')
readOct = readInt 8 isOctDigit (\d -> ord d - ord '0')
readHex = readInt 16 isHexDigit hex
where hex d = ord d - (if isDigit d then ord '0'
else ord (if isUpper d then 'A' else 'a')
- 10)
readInt :: Int -> (Char -> Bool) -> (Char -> Int) -> ReadS Int
readInt radix isDig digToInt s =
[(foldl1 (\n d -> n * radix + d) (map (fromInteger . digToInt) ds), r)
| (ds,r) <- nonnull isDig s ]
readSigned:: ReadS Int -> ReadS Int
readSigned readPos = readParen False read'
where read' r = read'' r ++
[(-x,t) | ("-",s) <- lex r,
(x,t) <- read'' s]
read'' r = [(n,s) | (str,s) <- lex r,
(n,"") <- readPos str]