| Copyright | © 2015–2019 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
Synopsis
- class (Ord (Token s), Ord (Tokens s)) => Stream s where
- type Token s :: *
- type Tokens s :: *
- tokenToChunk :: Proxy s -> Token s -> Tokens s
- tokensToChunk :: Proxy s -> [Token s] -> Tokens s
- chunkToTokens :: Proxy s -> Tokens s -> [Token s]
- chunkLength :: Proxy s -> Tokens s -> Int
- chunkEmpty :: Proxy s -> Tokens s -> Bool
- take1_ :: s -> Maybe (Token s, s)
- takeN_ :: Int -> s -> Maybe (Tokens s, s)
- takeWhile_ :: (Token s -> Bool) -> s -> (Tokens s, s)
- showTokens :: Proxy s -> NonEmpty (Token s) -> String
- reachOffset :: Int -> PosState s -> (SourcePos, String, PosState s)
- reachOffsetNoLine :: Int -> PosState s -> (SourcePos, PosState s)
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, take1_, takeN_, takeWhile_, showTokens, reachOffset
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.
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.
showTokens :: Proxy s -> NonEmpty (Token s) -> String Source #
Pretty-print non-empty stream of tokens. This function is also used to print single tokens (represented as singleton lists).
Since: 7.0.0
Arguments
| :: Int | Offset to reach |
| -> PosState s | Initial |
| -> (SourcePos, String, PosState s) | (See below) |
Given an offset o and initial PosState, adjust the state in such
a way that it starts at the offset.
Return three values (in order):
SourcePoswhich the given offsetopoints to.Stringrepresenting the line on which the given offsetois located. The line should satisfy a number of conditions that are described below.- The updated
PosStatewhich can be in turn used to locate another offseto'given thato' >= o.
The String representing the offending line in input stream should
satisfy the following:
- It should adequately represent location of token at the offset of
interest, that is, character at
sourceColumnof the returnedSourcePosshould correspond to the token at the offseto. - It should not include the newline at the end.
- It should not be empty, if the line happens to be empty, it
should be replaced with the string
"<empty line>". - Tab characters should be replaced by appropriate number of
spaces, which is determined by the
pstateTabWidthfield ofPosState.
Since: 7.0.0
Arguments
| :: Int | Offset to reach |
| -> PosState s | Initial |
| -> (SourcePos, PosState s) | Reached source position and updated state |
A version of reachOffset that may be faster because it doesn't need
to fetch the line at which the given offset in located.
The default implementation is this:
reachOffsetNoLine o pst = let (spos, _, pst')= reachOffset o pst in (spos, pst')
Since: 7.0.0