CAS command question

[parisse]

Programs are symbolic expressions of root node 'program' with 3 arguments: the arguments, the arguments*0 (not used currently), and a (list of) expressions to be executed. During evaluation, a local context is created where the arguments variable names are assigned to the arguments variables values and the list of expression is executed.

The general scheme for any CAS is : input is a whole string, parse it into a CAS expression, eval it from top rootnode recursively. There is no I/O from the CAS point of view, the computing kernel is completely separated from user interaction.

I disagree with DrD with the fact that in an educatonial environment, we should make softwares available that exactly support the syntax of textbook problems, students are not robots, we should explain students the logic behind so that they can adapt to any kind of software later. In a professional environment, it's different and being able to copy/paste without user intervention is desirable. The additional work will be done by a programmer that should take the time to understand how the software works, I have shown code slices in this thread which demonstrate how left/right can be used to extract the relevant information with more freedom for the user and more control on the syntax than with strings. Using strings instead of symbolic expressions shoud not be the normal choice because strings have no structure, and calling the parser is inefficient. But I have nothing against improving left and right for strings arguments if DrD really prefers to program with strings.