/// <summary>
/// Takes a lambda expression that maps the elements of the enumerable and returns an
/// enumerable of the elements after they were mapped.
/// </summary>
/// <param name="expression">The enumerable expression.</param>
/// <param name="selector">The mapping function.</param>
/// <returns>The enumerable after mapping.</returns>
public static EnumerableExpression Select(this EnumerableExpression expression, LambdaExpression selector)
{
Func <ParameterExpression, Expression> SelectorBody(Func <ParameterExpression, Expression> continuation)
{
Expression Inner(ParameterExpression curElem)
{
ParameterExpression newElemVar = Expression.Variable(selector.ReturnType, "newElem");
return(Expression.Block(
new[] { newElemVar },
Expression.Assign(newElemVar, selector.Substitute(curElem)),
continuation(newElemVar)));
}
return(Inner);
}
return(expression.SelectRaw(SelectorBody, selector.ReturnType));
}
/// <summary>
/// Takes an enumerable of element T, and an expression from T -> bool, and filters the
/// enumerable to elements where the predicate is true.
/// </summary>
/// <param name="expression">The enumerable to filter.</param>
/// <param name="predicate">The predicate to filter on.</param>
/// <returns>The filtered enumerable.</returns>
public static EnumerableExpression Where(this EnumerableExpression expression, LambdaExpression predicate)
{
return(expression.SelectRaw(
k => cur => Expression.IfThen(predicate.Substitute(cur), k(cur)),
expression.ElementType));
}