private static Variable FindVariable(
char aSymbol,
VariableDictionary aBoundVariables,
CollectedItems aCollectedItems)
{
if (aBoundVariables.ContainsVariableForSymbol(aSymbol))
{
return(aBoundVariables.Retrieve(aSymbol));
}
else
{
return(aCollectedItems.AddUnboundVariable(aSymbol));
}
}
public VariableDictionary CreateNewSetThatRebinds(char aSymbol, Variable aVariable)
{
VariableDictionary lUpdatedDictionary = new VariableDictionary();
foreach (char lSymbol in mVariables.Keys)
{
if (lSymbol != aSymbol)
{
lUpdatedDictionary.Add(lSymbol, mVariables[lSymbol]);
}
}
lUpdatedDictionary.Add(aSymbol, aVariable);
return(lUpdatedDictionary);
}
private static Matrix Parse(
string[] aExpressions,
CollectedItems aCollectedItems,
VariableDictionary aBoundVariables)
{
string lFirst = aExpressions[0];
if (aExpressions.Length == 1)
{
return(ParsePropositionalSubexpression(lFirst, aCollectedItems, aBoundVariables));
}
string[] lTail = aExpressions.Tail <string>();
if (AreUnariesFollowedByAQuantifier(aExpressions))
{
return(ParseUnaryOperatorOnTail(lFirst, lTail, aCollectedItems, aBoundVariables));
}
if (lFirst.IsQuantifier())
{
return(ParseQuantification(lFirst, lTail, aCollectedItems, aBoundVariables));
}
if (aExpressions.TakeWhile(fExpression => !fExpression.IsQuantifier()).Any(fToken => fToken.IsBinaryOperator()))
{
return(ParseBinaryOperator(aExpressions, aCollectedItems, aBoundVariables));
}
if (IsUnaryOperator(lFirst))
{
return(ParseUnaryOperatorOnTail(lFirst, lTail, aCollectedItems, aBoundVariables));
}
throw new ParseError("Could not parse \"{0}\"", string.Join("", aExpressions));
}
private static Matrix ParsePropositionalSubexpression(
string aExpression,
CollectedItems aCollectedItems,
VariableDictionary aBoundVariables)
{
if (aExpression.Matches(TwoTermProposition))
{
return(ParseTwoTermProposition(aExpression, aCollectedItems));
}
if (aExpression.Matches(Is))
{
return(aCollectedItems.AddUnaryPredication(
aCollectedItems.AddUnaryPredicate(aExpression[0]),
FindVariable(aExpression[1], aBoundVariables, aCollectedItems)));
}
if (aExpression.Matches(Are))
{
return(aCollectedItems.AddBinaryPredication(
aCollectedItems.AddBinaryPredicate(aExpression[1]),
FindVariable(aExpression[0], aBoundVariables, aCollectedItems),
FindVariable(aExpression[2], aBoundVariables, aCollectedItems)));
}
if (aExpression.Matches(TrueThat))
{
return(aCollectedItems.AddNullPredicate(aExpression[0]));
}
if (aExpression.Matches(IsTheSameAs))
{
return(aCollectedItems.AddIdentification(
FindVariable(aExpression[0], aBoundVariables, aCollectedItems),
FindVariable(aExpression[2], aBoundVariables, aCollectedItems)));
}
if (aExpression.Matches(ThereAreThisManyOfThese))
{
return(Factory.ThereAreThisManyOfThese(
UInt32.Parse(aExpression.Substring(0, aExpression.Length - 1)),
aCollectedItems.AddUnaryPredicate(aExpression[aExpression.Length - 1])));
}
if (aExpression.Matches(ThisManyOfTheseAreTrue))
{
List <Matrix> lPredicates = new List <Matrix>();
RegexMatch lMatch = ThisManyOfTheseAreTrue.Exec(aExpression);
for (int i = 0; i < lMatch[2].Length; i++)
{
lPredicates.Add(aCollectedItems.AddNullPredicate(lMatch[2][i]));
}
return(Factory.ThisManyOfTheseAreTrue(UInt32.Parse(lMatch[1]), lPredicates));
}
if (aExpression.Matches(ParenthesizedExpression))
{
return(Parse(
aExpression.Substring(1, aExpression.Length - 2).GetSubexpressions(),
aCollectedItems,
aBoundVariables));
}
throw new ParseError("Expected predication or parenthesized expression, found \"{0}\"", aExpression);
}
private static Matrix ParseBinaryOperator(
string[] aTokens,
CollectedItems aCollectedItems,
VariableDictionary aBoundVariables)
{
int lNumberOfTokensBeforeBinaryOperator = -1;
int lHighestPrecedenceFound = -1;
for (int i = 0; i < aTokens.Length; i++)
{
if (aTokens[i].IsBinaryOperator())
{
int lPrecedence = aTokens[i].PrecedenceOfBinaryOperator();
if (lPrecedence >= lHighestPrecedenceFound)
{
lHighestPrecedenceFound = lPrecedence;
lNumberOfTokensBeforeBinaryOperator = i;
}
}
if (aTokens[i].IsQuantifier())
{
break;
}
}
string[] lTokensBeforeLastBinaryOperator = aTokens.Subarray(0, lNumberOfTokensBeforeBinaryOperator);
string[] lTokensAfterLastBinaryOperator = aTokens.Subarray(
lNumberOfTokensBeforeBinaryOperator + 1,
aTokens.Length - lNumberOfTokensBeforeBinaryOperator - 1);
string lLastBinaryOperator = aTokens[lNumberOfTokensBeforeBinaryOperator];
if (lTokensBeforeLastBinaryOperator.Length == 0 || lTokensAfterLastBinaryOperator.Length == 0)
{
throw new ParseError("Could not parse \"{0}\"", string.Join("", aTokens));
}
Matrix lLeft = Parse(lTokensBeforeLastBinaryOperator, aCollectedItems, aBoundVariables);
Matrix lRight = Parse(lTokensAfterLastBinaryOperator, aCollectedItems, aBoundVariables);
if (lLastBinaryOperator.Matches(And))
{
return(Factory.And(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(Or))
{
return(Factory.Or(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(OnlyIf))
{
return(Factory.OnlyIf(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(IfAndOnlyIf))
{
return(Factory.IfAndOnlyIf(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(Nor))
{
return(Factory.Nor(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(Xor))
{
return(Factory.Xor(lLeft, lRight));
}
if (lLastBinaryOperator.Matches(NecessarilyOnlyIf))
{
return(Factory.NecessarilyOnlyIf(lLeft, lRight));
}
// The program should never reach this point.
throw new Exception();
}