xref: /external/antlr/antlr-3.4/runtime/CSharp2/Sources/Antlr3.Runtime/Antlr.Runtime/IIntStream.cs

/*
[The "BSD licence"]
Copyright (c) 2007-2008 Johannes Luber
Copyright (c) 2005-2007 Kunle Odutola
All rights reserved.

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modification, are permitted provided that the following conditions
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   notice, this list of conditions and the following disclaimer.
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   the documentation and/or other materials provided with the
   distribution.
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   derived from this software without specific prior WRITTEN permission.
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   submitted for inclusion in this work to the copyright owner or licensor
   shall be under the terms and conditions of this license, without any
   additional terms or conditions.

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namespace Antlr.Runtime
{
    using System;

	/// <summary>
    /// A simple stream of integers. This is useful when all we care about is the char
	/// or token type sequence (such as for interpretation).
	/// </summary>
	public interface IIntStream
	{
		void Consume();

		/// <summary>
        /// Get int at current input pointer + i ahead (where i=1 is next int)
		/// Negative indexes are allowed.  LA(-1) is previous token (token just matched).
		/// LA(-i) where i is before first token should yield -1, invalid char or EOF.
        /// </summary>
		int LA(int i);

		/// <summary>Tell the stream to start buffering if it hasn't already.</summary>
        /// <remarks>
        /// Executing Rewind(Mark()) on a stream should not affect the input position.
		/// The Lexer tracks line/col info as well as input index so its markers are
		/// not pure input indexes.  Same for tree node streams.													*/
        /// </remarks>
        /// <returns>Return a marker that can be passed to
        /// <see cref="IIntStream.Rewind(int)"/> to return to the current position.
        /// This could be the current input position, a value return from
        /// <see cref="IIntStream.Index"/>, or some other marker.</returns>
		int Mark();

		/// <summary>
        /// Return the current input symbol index 0..n where n indicates the
		/// last symbol has been read. The index is the symbol about to be
		/// read not the most recently read symbol.
		/// </summary>
		int Index { get; }

        /// <summary>
		/// Resets the stream so that the next call to
        /// <see cref="IIntStream.Index"/> would  return marker.
        /// </summary>
        /// <remarks>
        /// The marker will usually be <see cref="IIntStream.Index"/> but
        /// it doesn't have to be.  It's just a marker to indicate what
        /// state the stream was in.  This is essentially calling
        /// <see cref="IIntStream.Release"/> and <see cref="IIntStream.Seek"/>.
        /// If there are other markers created after the specified marker,
        /// this routine must unroll them like a stack.  Assumes the state the
        /// stream was in when this marker was created.
        /// </remarks>
		void Rewind(int marker);

		/// <summary>
		/// Rewind to the input position of the last marker.
		/// </summary>
		/// <remarks>
		/// Used currently only after a cyclic DFA and just before starting
		/// a sem/syn predicate to get the input position back to the start
		/// of the decision. Do not "pop" the marker off the state.  Mark(i)
		/// and Rewind(i) should balance still. It is like invoking
		/// Rewind(last marker) but it should not "pop" the marker off.
		/// It's like Seek(last marker's input position).
		/// </remarks>
		void Rewind();

		/// <summary>
        /// You may want to commit to a backtrack but don't want to force the
		/// stream to keep bookkeeping objects around for a marker that is
		/// no longer necessary.  This will have the same behavior as
        /// <see cref="IIntStream.Rewind(int)"/> except it releases resources without
        /// the backward seek.
		/// </summary>
		/// <remarks>
		/// This must throw away resources for all markers back to the marker
		/// argument. So if you're nested 5 levels of Mark(), and then Release(2)
		/// you have to release resources for depths 2..5.
		/// </remarks>
		void Release(int marker);

		/// <summary>
        /// Set the input cursor to the position indicated by index.  This is
		/// normally used to seek ahead in the input stream.
        /// </summary>
        /// <remarks>
        /// No buffering is required to do this unless you know your stream
        /// will use seek to move backwards such as when backtracking.
		///
		/// This is different from rewind in its multi-directional requirement
        /// and in that its argument is strictly an input cursor (index).
		///
		/// For char streams, seeking forward must update the stream state such
		/// as line number.  For seeking backwards, you will be presumably
        /// backtracking using the
        /// <see cref="IIntStream.Mark"/>/<see cref="IIntStream.Rewind(int)"/>
        /// mechanism that restores state and so this method does not need to
        /// update state when seeking backwards.
		///
		/// Currently, this method is only used for efficient backtracking using
		/// memoization, but in the future it may be used for incremental parsing.
		///
		/// The index is 0..n-1. A seek to position i means that LA(1) will return
		/// the ith symbol.  So, seeking to 0 means LA(1) will return the first
		/// element in the stream.
        /// </remarks>
		void Seek(int index);

		/// <summary>Returns the size of the entire stream.</summary>
        /// <remarks>
        /// Only makes sense for streams that buffer everything up probably,
        /// but might be useful to display the entire stream or for testing.
		/// This value includes a single EOF.
        /// </remarks>
        int Count { get; }

		/// <summary>
		/// Where are you getting symbols from?  Normally, implementations will
		/// pass the buck all the way to the lexer who can ask its input stream
		/// for the file name or whatever.
		/// </summary>
		string SourceName {
			get;
		}
	}
}