private static SwitchExpression CompileState <OutputT>(TransducerState <Char, OutputT> state, ParameterExpression reader, ParameterExpression output, LabelTarget @return, Int32 depth)
{
var idx = 0;
var cases = new SwitchCase[state.TransitionTable.Count];
foreach (KeyValuePair <Char, TransducerState <Char, OutputT> > statePair in state.TransitionTable)
{
cases[idx++] = Expression.SwitchCase(
CompileState(statePair.Value, reader, output, @return, depth + 1),
Expression.Constant((Char?)statePair.Key)
);
}
return(Expression.Switch(
GExpression.MethodCall <ICodeReader>(reader, r => r.Peek(depth), depth),
state.IsTerminal
? Expression.Block(
GExpression.MethodCall <ICodeReader>(reader, r => r.Advance(0), depth + 1),
Expression.Assign(output, Expression.Constant(state.Output)),
Expression.Return(@return, Expression.Constant(true))
)
: (Expression)Expression.Return(@return, Expression.Constant(false)),
cases
));
}
private static SwitchExpression CompileState <TTokenType, OutputT>(TransducerState <Token <TTokenType>, OutputT> state, ParameterExpression reader, ParameterExpression output, LabelTarget @return, Int32 depth)
where TTokenType : notnull
{
var idx = 0;
var cases = new SwitchCase[state.TransitionTable.Count];
foreach (KeyValuePair <Token <TTokenType>, TransducerState <Token <TTokenType>, OutputT> > statePair in state.TransitionTable)
{
cases[idx++] = Expression.SwitchCase(
CompileState(statePair.Value, reader, output, @return, depth + 1),
Expression.Constant(statePair.Key)
);
}
return(Expression.Switch(
GExpression.MethodCall <ITokenReader <TTokenType> >(reader, r => r.Lookahead(depth), depth),
state.IsTerminal
? Expression.Block(
GExpression.MethodCall <ITokenReader <TTokenType> >(reader, r => r.Skip(0), depth + 1),
Expression.Assign(output, Expression.Constant(state.Output)),
Expression.Return(@return, Expression.Constant(true))
)
: (Expression)Expression.Constant(false),
cases
));
}
/// <summary>
/// Attempts to execute a transducer with content from a <see cref="StringCodeReader" />. If the
/// state reached is not a terminal state, the reader is rewinded to it's initial position.
/// </summary>
/// <typeparam name="OutputT"></typeparam>
/// <param name="transducer"></param>
/// <param name="reader"></param>
/// <param name="output"></param>
/// <returns>Whether the state reached was a terminal state.</returns>
public static Boolean TryExecute <OutputT>(this Transducer <Char, OutputT> transducer, ICodeReader reader, [MaybeNull] out OutputT output)
{
if (transducer is null)
{
throw new ArgumentNullException(nameof(transducer));
}
if (reader is null)
{
throw new ArgumentNullException(nameof(reader));
}
var start = reader.Position;
TransducerState <Char, OutputT> state = transducer.InitialState;
while (reader.Position != reader.Length)
{
if (!state.TransitionTable.TryGetValue(reader.Peek() !.Value, out TransducerState <Char, OutputT>?tmp))
{
break;
}
state = tmp;
reader.Advance(1);
}
if (state.IsTerminal)
{
output = state.Output;
return(true);
}
reader.Restore(start);
// Since the analyzer doesn't seems to obey [MaybeNull], we ignore the warning
output = default;
return(false);
}
/// <summary>
/// Attempts to execute the state machine against the <see cref="TokenReader{TTokenType}" />
/// </summary>
/// <typeparam name="TTokenType"></typeparam>
/// <typeparam name="OutputT"></typeparam>
/// <param name="transducer"></param>
/// <param name="reader"></param>
/// <param name="output"></param>
/// <returns></returns>
public static Boolean TryExecute <TTokenType, OutputT>(this Transducer <Token <TTokenType>, OutputT> transducer, ITokenReader <TTokenType> reader, [MaybeNull] out OutputT output)
where TTokenType : notnull
{
if (reader == null)
{
throw new ArgumentNullException(nameof(reader));
}
var offset = 0;
TransducerState <Token <TTokenType>, OutputT> state = transducer.InitialState;
while (reader.Position < reader.Length)
{
if (!state.TransitionTable.TryGetValue(reader.Lookahead(offset), out TransducerState <Token <TTokenType>, OutputT>?tmp))
{
break;
}
state = tmp;
offset++;
}
if (state.IsTerminal)
{
reader.Skip(offset + 1);
output = state.Output;
return(true);
}
output = default;
return(false);
}
