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// Copyright 2017-present Strumenta and contributors, licensed under Apache 2.0.
// Copyright 2024-present Strumenta and contributors, licensed under BSD 3-Clause.
package org.antlr.v4.kotlinruntime
/**
* A simple stream of symbols whose values are represented as integers.
* This interface provides *marked ranges* with support for a minimum level
* of buffering necessary to implement arbitrary lookahead during prediction.
* For more information on marked ranges, see [mark].
*
* **Initializing methods:** some methods in this interface have
* unspecified behavior if no call to an initializing method has occurred after
* the stream was constructed. The following is a list of initializing methods:
*
* - [LA]
* - [consume]
* - [size]
*/
public interface IntStream {
public companion object {
/**
* The value returned by [LA] when the end of the stream is reached.
*/
public const val EOF: Int = -1
/**
* The value returned by [sourceName] when the actual name of the
* underlying source is not known.
*/
public const val UNKNOWN_SOURCE_NAME: String = ""
}
/**
* Gets the name of the underlying symbol source.
*
* This method returns a non-`null`, non-empty string.
* If such a name is not known, this method returns [UNKNOWN_SOURCE_NAME].
*/
public val sourceName: String
/**
* Consumes the current symbol in the stream.
*
* This method has the following effects:
*
* - **Forward movement:** the value of [index] before calling
* this method is less than the value of [index] after calling this method
* - **Ordered lookahead:** the value of `LA(1)` before calling
* this method becomes the value of `LA(-1)` after calling this method
*
* Note that calling this method does not guarantee that [index] is
* incremented by exactly `1`, as that would preclude the ability to implement
* filtering streams (e.g., [CommonTokenStream] which distinguishes
* between "on-channel" and "off-channel" tokens).
*
* @throws IllegalStateException If an attempt is made to consume the
* end of the stream (i.e., if `LA(1) == `[EOF] before calling `consume`)
*/
public fun consume()
/**
* Gets the value of the symbol at offset [i] from the current position.
*
* When [i] `== 1`, this method returns the value of the current
* symbol in the stream (which is the next symbol to be consumed).
* When [i] `== -1`, this method returns the value of the previously read
* symbol in the stream. It is not valid to call this method with
* [i] `== 0`, but the specific behavior is unspecified because this
* method is frequently called from performance-critical code.
*
* This method is guaranteed to succeed if any of the following are true:
*
* - [i] `> 0`
* - [i] `== -1` and [index] returns a value greater than the value
* of [index] after the stream was constructed and `LA(1)` was called
* in that order. Specifying the current [index] relative to the index
* after the stream was created allows for filtering implementations
* that do not return every symbol from the underlying source.
* Specifying the call to `LA(1)` allows for lazily initialized streams
* - `LA(i)` refers to a symbol consumed within a marked region
* that has not yet been released
*
* If [i] represents a position at or beyond the end of the stream,
* this method returns [EOF].
*
* The return value is unspecified if [i] `< 0` and fewer than `-`[i]
* calls to [consume] have occurred from the beginning of the stream
* before calling this method.
*
* @throws UnsupportedOperationException If the stream does not support
* retrieving the value of the specified symbol
*/
@Suppress("FunctionName")
public fun LA(i: Int): Int
/**
* A mark provides a guarantee that [seek] operations will be
* valid over a "marked range" extending from the index where [mark]
* was called to the current [index].
*
* This allows the use of streaming input sources by specifying the minimum
* buffering requirements to support arbitrary lookahead during prediction.
*
* The returned mark is an opaque handle (type `Int`) which is passed
* to [release] when the guarantees provided by the marked range are no longer necessary.
*
* When calls to [mark]/[release] are nested, the marks must be released
* in reverse order of which they were obtained. Since marked regions are
* used during performance-critical sections of prediction, the specific
* behavior of invalid usage is unspecified (i.e., a mark is not released, or
* a mark is released twice, or marks are not released in reverse order from
* which they were created).
*
* The behavior of this method is unspecified if no call to an
* *initializing method* has occurred after this stream was constructed.
*
* This method does not change the current position in the input stream.
*
* The following example shows the use of [mark], [release], [index], and
* [seek] as part of an operation to safely work within a marked region,
* then restore the stream position to its original value and release the mark.
*
* ```
* val stream: IntStream = ...
* var index = -1
* val mark = stream.mark()
*
* try {
* index = stream.index()
* // Perform work here...
* } finally {
* if (index != -1) {
* stream.seek(index)
* }
*
* stream.release(mark)
* }
* ```
*
* @return An opaque marker which should be passed to [release]
* when the marked range is no longer required
*/
public fun mark(): Int
/**
* This method releases a marked range created by a call to [mark].
*
* Calls to [release] must appear in the reverse order of the corresponding
* calls to [mark]. If a mark is released twice, or if marks are not released
* in reverse order of the corresponding calls to [mark], the behavior is unspecified.
*
* For more information and an example, see [mark].
*
* @param marker A marker returned by a call to [mark]
* @see mark
*/
public fun release(marker: Int)
/**
* Return the index into the stream of the input symbol referred to by `LA(1)`.
*
* The behavior of this method is unspecified if no call to an
* *initializing method* has occurred after this stream was constructed.
*/
public fun index(): Int
/**
* Set the input cursor to the position indicated by [index].
*
* If the specified [index] lies past the end of the stream, the operation
* behaves as though [index] was the index of the `EOF` symbol.
* After this method returns without throwing an exception, then at least
* one of the following will be true.
*
* - [index] will return the index of the first symbol appearing
* at or after the specified `index`. Specifically, implementations
* which filter their sources should automatically adjust `index`
* forward the minimum amount required for the operation to target
* a non-ignored symbol
* - `LA(1)` returns [EOF]
*
* This operation is guaranteed to not throw an exception if [index]
* lies within a marked region. For more information on marked regions,
* see [mark]. The behavior of this method is unspecified if no call to
* an *initializing method* has occurred after this stream was constructed
*
* @param index The absolute index to seek to
*
* @throws IllegalArgumentException If [index] is less than `0`
* @throws UnsupportedOperationException If the stream does not support
* seeking to the specified [index]
*/
public fun seek(index: Int)
/**
* Returns the total number of symbols in the stream, including a single `EOF` symbol.
*
* @throws UnsupportedOperationException If the size of the stream is unknown
*/
public fun size(): Int
}
