Not null scheme

How do we use them? Scheme provides us with a uniform syntax for invoking functions: function arg1 arg Arguments are passed by value except with special forms , discussed later, to allow for nice things like short circuiting. In Scheme, lists are unbounded, possibly heterogeneous collections of data.

Examples: x elmer fudd 2 3 5 7 11 2 3 x y "zoo" 2. Scheme waits for the user to type an expression, reads it, evaluates it, and prints the return value. Scheme expressions often called S-Expressions , for Symbolic Expressions are either lists or atoms. Lists are composed of other S-Expressions note the recursive definition. Lists are often used to represent function calls, where the list consists of a function name followed by its arguments.

However, lists can also used to represent arbitrary collections of data. Symbols are treated as variables, and to evaluate them, their bindings are looked up in the current environment. For lists, the first element specifies the function. The remaining elements of the list specify the arguments. Evaluate the first element in the current environment to find the function, and evaluate each of the arguments in the current environment, and call the function on these values.

Because Scheme will treat the atom elmer as a variable name and try to look for its binding, which it won't find. We therefore need to "quote" the names elmer and fudd , which means that we want scheme to treat them literally. Scheme provides syntax for doing this. The evaluation for quoted objects is that a quoted object evalutes to itself. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.

Learn more. Best way to check if a list is not null? Ask Question. Asked 10 years, 4 months ago. Active 10 years, 4 months ago. Viewed 34k times. What do you mean by 'will make Scheme think that I am trying to call a function'?

I looked up the complaint on Google and apparently Scheme is trying to call the function with the name of the first item in the list, and since that function doesn't exist, Scheme complains — wrongusername. Sounds like you are not quoting the list, iow 1 2 3 vs ' 1 2 3 with the latter being correct.

Sorry, I have no idea what you mean, please provide some code samples, what you expect, and what you actually get, error message also welcome as well as your Scheme implementation. Hi Dimitri, First congrats for such knowledge sharing!

Hi Dimitri, thanks for the app link. I am trying to test the whole flow, but already tried to reset password with 3 different registered users gmail. Any chance the mail send fucntion at yout apex environment is down? Best Renato. Thanks a lot, Renato.

Hi Dimitri I tried to use you package on oracle apex Hi Dimitri, love your work. I'm trying to use a common package for authentication across several similar apps each for a different client. Any pointers on how to send the extra parameter to my auth proc? Cheers Richard. Hi, can you share source of this application, i am very new with Oracle Apex and i need to see how did you design the login screen.

Hi, Thanks for the solution. But my concern if that Our application use two authentications , one from Database table users and other from LDAP active directory. As the authentication scheme allows to have only one scheme as current then how can I use both at the same time. Please share some information for this issue. Regards, Richa Gandhi omegacoder. Hi Dimitri, great work and great idea. But please, for the sake of the beginners like us, can you host the source somewhere for us to really understand everything you want us to learn, please.

This is more of a problem than solutions to some of us. You might want to consider Github, please. More blessings, sir! I have been struggling with you steps since two years now, still no way. Please, save our souls. Source code, please. Sorry for my previous commemts, please, I would be glad if could be removed even. All odds crushed, except for a little error that's proving stubborn, but I would be happy if you could be of an help over it. Thank you very much for coming up with this blog.

Hi Dimitri, can you share source of this application, i am trying but can't do which you doing with Oracle Apex and i need to see how did you design the login screen. Hi Dimitri, Thanks for sharing this process. I have tried granting access for my user but receive another error "table does not exist".

I am assuming that the ability to access these functions are embedded deep in APEX v Any ideas? Brett, grant execute on sys. Dimitri, One thing I have noticed, if your application is in debug mode, the debug messages log shows the users salt, hash and password in the nobody log. Is there anyway to have this not show other than disabling debug, but we use that for our Testing and Development Apps?

Thanks Dustin. I tried to execute grant execute but receive an error "table or view not found". How we can see clearly apex pages and their code Not good in Apex. Can you put apex pages images or may be create sample app which we can import?

Thanks Dimiri, Awesome!!! You did the excellent job. I am new to APEX. My requirement is very close to your Multiplication Table Game.

Could you please share your source to download from GIT or email to me. I will import your app to my workspace. Tons of Thanks Ashok. Hi Dimitri, I have read through your post and watch the video and it has really added to my knowledge. However, I am not sure what I am doing wrongly, am using Apex Clicking the register button just redirect me back to Login region without inserting any value in user table?

Is there a better way to debug where the process is breaking? Hi Dimitri, Wonderful post.