Hi, I have a question: Short version: If I want to hide the implementation of a data-type "Stack a" from the rest of the program, do I need to put its definition in a separate file? Long version: I want to use a stack, and I might implement it as a list, but I want to hide the implementation from the rest of the program. This is how I understand abstract data type. In "The Craft of Functional Programming", this seems to be implemented by putting each data type into a separate module and only exporting parts of the definitions. In "The Haskell School of Expression", this seems not to be used at all. In the lecture notes at (http://www.dcs.shef.ac.uk/~mps/courses/com2020/adts.pdf), type classes are used for abstract data types. It seems to me that this approach does not hide any parts of any definition, but only requires that all instances of class stack have functions pop and push of the correct types. I am interested in hiding parts of definitions. In the report, I did not find any mention of a requirement to have different modules in separate files, but I have not managed to put several modules in the same file using ghci. I would like to keep my small program in one literate-haskell tex-file and still be able to hide some definitions from others. Is this possible? One option would of course be to write a script that separates the code into different and then compiles the entire program. Thanks in advance! / johan grönqvist