object EvaluateWhereClause(Runtime.PassiveExpression expr, Runtime.Pattern lastPattern, ScriptThread thread)
{
// instantiate where-clause pattern
var patt = Pattern.Instantiate(thread);
patt.CopyBoundVariables(lastPattern);
// perform matching
var result = patt.Match(expr);
if (result)
{
// store last recognized pattern as a local variable
thread.SetLastPattern(patt);
// match succeeded, return result expression
if (ResultExpression != null)
{
return ResultExpression.Evaluate(thread);
}
// match succeeded, evaluate more conditions
if (MoreConditions != null)
{
return MoreConditions.Evaluate(thread);
}
}
// matching failed, return nothing
return null;
}
protected override object DoEvaluate(ScriptThread thread)
{
// standard prolog
thread.CurrentNode = this;
// evaluate pattern and copy bound variables of the current block
var patt = Pattern.Instantiate(thread);
if (BlockPattern != null)
{
patt.CopyBoundVariables(BlockPattern);
}
object result = null;
// if pattern is recognized, calculate new expression and return true
var success = patt.Match(InputExpression);
if (success)
{
// store last recognized pattern as a local variable
thread.SetLastPattern(patt);
// simple sentence
if (Expression != null)
{
result = Expression.Evaluate(thread);
}
// sentence with a where- or when-clause
else if (Conditions != null)
{
result = Conditions.Evaluate(thread);
}
}
// standard epilog
thread.CurrentNode = Parent;
return result;
}