Here's a way to do it :
Expression<Func<Foo, bool>> IsSuperhuman = x => x.CanFly && x.HasXRayVision;
Expression<Func<Foo, bool>> IsSuperheroine = AndAlso(IsSuperhuman, x => x.IsFemale);
...
public static Expression<Func<T, TResult>> AndAlso<T, TResult>(Expression<Func<T, TResult>> expr1, Expression<Func<T, TResult>> expr2)
{
var arg = Expression.Parameter(typeof(T), expr1.Parameters[0].Name);
var andExpr = Expression.AndAlso(
ReplaceParameter(expr1.Body, expr1.Parameters[0], arg),
ReplaceParameter(expr2.Body, expr2.Parameters[0], arg));
return Expression.Lambda<Func<T, TResult>>(andExpr, arg);
}
public static Expression ReplaceParameter(Expression expr, ParameterExpression oldParam, ParameterExpression newParam)
{
return new ReplaceParameterVisitor(oldParam, newParam).Visit(expr);
}
internal class ReplaceParameterVisitor : ExpressionVisitor
{
private ParameterExpression _oldParam;
private ParameterExpression _newParam;
public ReplaceParameterVisitor(ParameterExpression oldParam, ParameterExpression newParam)
{
_oldParam = oldParam;
_newParam = newParam;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (node == _oldParam)
return _newParam;
return node;
}
}
It is probably not the simplest way to do it, but it works...