| Copyright | © 2015–2017 Megaparsec contributors |
|---|---|
| License | FreeBSD |
| Maintainer | Mark Karpov <markkarpov92@gmail.com> |
| Stability | experimental |
| Portability | portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Text.Megaparsec.Stream
Description
Megaparsec's input stream facilities.
You probably do not want to import this module directly because Text.Megaparsec re-exports it anyway.
Since: 6.0.0
Documentation
class (Ord (Token s), Ord (Tokens s)) => Stream s where Source #
Type class for inputs that can be consumed by the library.
Minimal complete definition
tokensToChunk, chunkToTokens, chunkLength, advance1, advanceN, take1_, takeN_, takeWhile_
Associated Types
Type of token in the stream.
Type of “chunk” of the stream.
Methods
tokenToChunk :: Proxy s -> Token s -> Tokens s Source #
Lift a single token to chunk of the stream. The default implementation is:
tokenToChunk pxy = tokensToChunk pxy . pure
However for some types of stream there may be a more efficient way to lift.
tokensToChunk :: Proxy s -> [Token s] -> Tokens s Source #
The first method that establishes isomorphism between list of tokens and chunk of the stream. Valid implementation should satisfy:
chunkToTokens pxy (tokensToChunk pxy ts) == ts
chunkToTokens :: Proxy s -> Tokens s -> [Token s] Source #
The second method that establishes isomorphism between list of tokens and chunk of the stream. Valid implementation should satisfy:
tokensToChunk pxy (chunkToTokens pxy chunk) == chunk
chunkLength :: Proxy s -> Tokens s -> Int Source #
Return length of a chunk of the stream.
chunkEmpty :: Proxy s -> Tokens s -> Bool Source #
Check if a chunk of the stream is empty. The default implementation
is in terms of the more general chunkLength:
chunkEmpty pxy ts = chunkLength pxy ts <= 0
However for many streams there may be a more efficient implementation.
positionAt1 :: Proxy s -> SourcePos -> Token s -> SourcePos Source #
Set source position at given token. By default, the given
SourcePos (second argument) is just returned without looking at the
token. This method is important when your stream is a collection of
tokens where every token knows where it begins in the original input.
positionAtN :: Proxy s -> SourcePos -> Tokens s -> SourcePos Source #
The same as positionAt1, but for chunks of the stream. The function
should return the position where the entire chunk begins. Again, by
default the second argument is returned without modifications and the
chunk is not looked at.
advance1 :: Proxy s -> Pos -> SourcePos -> Token s -> SourcePos Source #
Advance position given a single token. The returned position is the position right after the token, or the position where the token ends.
advanceN :: Proxy s -> Pos -> SourcePos -> Tokens s -> SourcePos Source #
Advance position given a chunk of stream. The returned position is the position right after the chunk, or the position where the chunk ends.
take1_ :: s -> Maybe (Token s, s) Source #
Extract a single token form the stream. Return Nothing if the
stream is empty.
takeN_ :: Int -> s -> Maybe (Tokens s, s) Source #
takeN_ n sn, or if the
stream is too short, the rest of the stream. Valid implementation
should follow the rules:
- If the requested length
nis 0 (or less),Nothingshould never be returned, insteadJust("", s)""stands for the empty chunk, andsis the original stream (second argument). - If the requested length is greater than 0 and the stream is
empty,
Nothingshould be returned indicating end of input. - In other cases, take chunk of length
n(or shorter if the stream is not long enough) from the input stream and return the chunk along with the rest of the stream.
takeWhile_ :: (Token s -> Bool) -> s -> (Tokens s, s) Source #
Extract chunk of the stream taking tokens while the supplied
predicate returns True. Return the chunk and the rest of the stream.
For many types of streams, the method allows for significant performance improvements, although it is not strictly necessary from conceptual point of view.