public Rule(Expression pattern, Expression replacement, Func<IDictionary<string, Expression>, bool> conditions)
{
this.pattern = pattern;
this.replacement = replacement;
this.conditions = conditions;
matches = new Dictionary<string, Expression>();
}
public double Calculate(Expression expr)
{
Expression simplified = simplifier.Simplify(expr);
if (!(simplified is NumberExpression))
throw new Exception("Expression can't be calculated");
return ((NumberExpression)simplified).Value;
}
public Expression Apply(Expression expr)
{
matches.Clear();
bool matching = match(expr);
if (matching == false)
return null;
Expression result = applyMatches((new EliminateSubtractions(replacement)).Result, matches);
return result;
}
private Expression applyMatches(Expression expr, IDictionary<string, Expression> matches)
{
if (expr is VariableExpression)
{
VariableExpression vexpr = (VariableExpression)expr;
if (matches.ContainsKey(vexpr.Name))
return matches[vexpr.Name];
return vexpr;
}
else if (expr is FunctionExpression)
{
FunctionExpression fexpr = (FunctionExpression)expr;
IList<Expression> args = new List<Expression>();
foreach (Expression arg in fexpr.Arguments)
args.Add(applyMatches(arg, matches));
return Expression.Function(fexpr.Name, args);
}
else if (expr is BinaryExpression)
{
BinaryExpression bexpr = (BinaryExpression)expr;
Expression left = applyMatches(bexpr.Left, matches);
Expression right = applyMatches(bexpr.Right, matches);
/*
if (bexpr.Operator == Binary.Subtract)
{
if (right is NumberExpression)
{
NumberExpression nright = (NumberExpression)right;
right = Expression.Number(-nright.Value);
}
else
right = Expression.Multiply(Expression.Number(-1), right);
return Expression.Add(left, right);
}
*/
return Expression.FromBinary(bexpr.Operator, left, right);
}
return expr;
}
public Rule(Expression pattern, Expression replacement)
: this(pattern, replacement, d => true)
{
}
private bool match(Expression expr, Expression pattern)
{
if (!(pattern is VariableExpression))
{
if (!expr.GetType().Equals(pattern.GetType()))
return false;
if (pattern is BinaryExpression)
{
BinaryExpression bexpr = (BinaryExpression)expr;
BinaryExpression bpattern = (BinaryExpression)pattern;
if (bexpr.Operator != bpattern.Operator)
return false;
return match(bexpr.Left, bpattern.Left) && match(bexpr.Right, bpattern.Right);
}
else if (pattern is FunctionExpression)
{
FunctionExpression fexpr = (FunctionExpression)expr;
FunctionExpression fpattern = (FunctionExpression)pattern;
if (fexpr.Name != fpattern.Name || fexpr.Arguments.Count != fpattern.Arguments.Count)
return false;
bool matching = true;
for (int i = 0; i < fexpr.Arguments.Count; i++)
matching = matching && match(fexpr.Arguments[i], fpattern.Arguments[i]);
return matching;
}
return expr.Equals(pattern);
}
else
{
VariableExpression vpattern = (VariableExpression)pattern;
string name = vpattern.Name;
if (matches.ContainsKey(name))
{
Expression fmatch = matches[name];
if (!expr.Equals(fmatch))
return false;
}
matches[name] = expr;
return true;
}
}
private bool match(Expression expr)
{
matches.Clear();
bool matching = match(expr, pattern);
return matching && conditions(matches);
}
public Calculator(Expression expr, IVariableScope variables = null, IFunctionScope functions = null)
: this(variables, functions)
{
this.result = Calculate(expr);
}