FastString

There are two principal string types used internally by GHC:

FastString

• A compact, hash-consed, representation of character strings.
• Comparison is O(1), and you can get a Unique from them.
• Generated by fsLit.
• Turn into SDoc with ftext.

LitString

• Just a wrapper for the Addr# of a C string (Ptr CChar).
• Practically no operations.
• Outputing them is fast.
• Generated by sLit.
• Turn into SDoc with ptext
• Requires manual memory management. Improper use may lead to memory leaks or dangling pointers.
• It assumes Latin-1 as the encoding, therefore it cannot represent arbitrary Unicode strings.

Use LitString unless you want the facilities of FastString.

ByteString

fastStringToByteString :: FastString -> ByteString

mkFastStringByteString :: ByteString -> FastString

Create a FastString from an existing ForeignPtr; the difference between this and mkFastStringBytes is that we don't have to copy the bytes if the string is new to the table.

fastZStringToByteString :: FastZString -> ByteString

unsafeMkByteString :: String -> ByteString

hashByteString :: ByteString -> Int

FastZString

data FastZString

Instances

NFData FastZString

Methods

rnf :: FastZString -> ()

hPutFZS :: Handle -> FastZString -> IO ()

zString :: FastZString -> String

lengthFZS :: FastZString -> Int

FastStrings

data FastString

A FastString is an array of bytes, hashed to support fast O(1) comparison. It is also associated with a character encoding, so that we know how to convert a FastString to the local encoding, or to the Z-encoding used by the compiler internally.

FastStrings support a memoized conversion to the Z-encoding via zEncodeFS.

Constructors

FastString

Fields

• uniq :: !Int
• n_chars :: !Int
• fs_bs :: !ByteString
• fs_ref :: !(IORef (Maybe FastZString))

Instances

Eq FastString

Methods

(==) :: FastString -> FastString -> Bool

(/=) :: FastString -> FastString -> Bool

Data FastString

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> FastString -> c FastString

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c FastString

toConstr :: FastString -> Constr

dataTypeOf :: FastString -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c FastString)

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c FastString)

gmapT :: (forall b. Data b => b -> b) -> FastString -> FastString

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> FastString -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> FastString -> r

gmapQ :: (forall d. Data d => d -> u) -> FastString -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> FastString -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> FastString -> m FastString

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> FastString -> m FastString

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> FastString -> m FastString

Ord FastString

Methods

compare :: FastString -> FastString -> Ordering

(<) :: FastString -> FastString -> Bool

(<=) :: FastString -> FastString -> Bool

(>) :: FastString -> FastString -> Bool

(>=) :: FastString -> FastString -> Bool

max :: FastString -> FastString -> FastString

min :: FastString -> FastString -> FastString

Show FastString

Methods

showsPrec :: Int -> FastString -> ShowS

show :: FastString -> String

showList :: [FastString] -> ShowS

IsString FastString

Methods

fromString :: String -> FastString

Monoid FastString

Methods

mempty :: FastString

mappend :: FastString -> FastString -> FastString

mconcat :: [FastString] -> FastString

Outputable FastString

Methods

ppr :: FastString -> SDoc

pprPrec :: Rational -> FastString -> SDoc

Uniquable FastString

Methods

getUnique :: FastString -> Unique

Binary FastString

Methods

put_ :: BinHandle -> FastString -> IO ()

put :: BinHandle -> FastString -> IO (Bin * FastString)

get :: BinHandle -> IO FastString

Construction

fsLit :: String -> FastString

mkFastString :: String -> FastString

Creates a UTF-8 encoded FastString from a String

mkFastStringBytes :: Ptr Word8 -> Int -> FastString

mkFastStringByteList :: [Word8] -> FastString

Creates a FastString from a UTF-8 encoded [Word8]

mkFastStringForeignPtr :: Ptr Word8 -> ForeignPtr Word8 -> Int -> IO FastString

Create a FastString from an existing ForeignPtr; the difference between this and mkFastStringBytes is that we don't have to copy the bytes if the string is new to the table.

mkFastString# :: Addr# -> FastString

Deconstruction

unpackFS :: FastString -> String

Unpacks and decodes the FastString

bytesFS :: FastString -> [Word8]

Gives the UTF-8 encoded bytes corresponding to a FastString

Encoding

zEncodeFS :: FastString -> FastZString

Returns a Z-encoded version of a FastString. This might be the original, if it was already Z-encoded. The first time this function is applied to a particular FastString, the results are memoized.

Operations

uniqueOfFS :: FastString -> Int

lengthFS :: FastString -> Int

Returns the length of the FastString in characters

nullFS :: FastString -> Bool

Returns True if the FastString is empty

appendFS :: FastString -> FastString -> FastString

headFS :: FastString -> Char

tailFS :: FastString -> FastString

concatFS :: [FastString] -> FastString

consFS :: Char -> FastString -> FastString

nilFS :: FastString

Outputing

hPutFS :: Handle -> FastString -> IO ()

Outputs a FastString with no decoding at all, that is, you get the actual bytes in the FastString written to the Handle.

Internal

getFastStringTable :: IO [[FastString]]

hasZEncoding :: FastString -> Bool

Returns True if this FastString is not Z-encoded but already has a Z-encoding cached (used in producing stats).

LitStrings

type LitString = Ptr Word8

A LitString is a pointer to some null-terminated array of bytes.

Construction

sLit :: String -> LitString

mkLitString# :: Addr# -> LitString

Wrap an unboxed address into a LitString.

mkLitString :: String -> LitString

Encode a String into a newly allocated LitString using Latin-1 encoding. The original string must not contain non-Latin-1 characters (above codepoint 0xff).

Deconstruction

unpackLitString :: LitString -> String

Decode a LitString back into a String using Latin-1 encoding. This does not free the memory associated with LitString.

Operations

lengthLS :: LitString -> Int

Compute the length of a LitString, which must necessarily be null-terminated.