Variable by itself on a line: meaning?

Hi Proto,

Yes, the variable on its own line, if it is the last thing in a let, procedure etc. will return the value of that variable from that block (procedure, let, progn, ...).  The return() statement is for the prog() construct. Note also that some programming constructs have useful return values, such as 'case' and 'cond', but others are not so useful (e.g. 'for' and 'foreach' unless it is used with another construct like 'mapcar'). I do not personally like 'prog-return' blocks as it can be difficult to work out the flow of control with arbitrary exits in the middle of the prog code block.

Best regards,

Lawrence.

Hi Lawrence,

Thank you for your detailed explanation -- it makes sense now. I am fairly experienced with different programming languages (C/C++, Python, Tcl), but SKILL is just something else. It has some unusual syntax that still confuses the heck out of me

Cheers,

Proto

Hi Lawrence,

Thank you for your detailed explanation -- it makes sense now. I am fairly experienced with different programming languages (C/C++, Python, Tcl), but SKILL is just something else. It has some unusual syntax that still confuses the heck out of me

Cheers,

Proto

Hi Proto,

SKILL is essentially a LISP underneath - it just has some alternative input syntax to make the code look more C-like by allowing infix operators - so that you can use (for example):

a=a+2*3

rather than:

(setq a (plus a (times 2 3)))

(both work in SKILL though and are entirely equivalent). One key principle to understand in SKILL is that everything is a function (so every operator, everything you call, corresponds to a function) and all functions have a return value, whether you use it or not. Because of that, there is a principle in most expressions that the return value is the last thing computed - so the return value of a let() is the last thing computed, as is the return value of a procedure(). There are a few exceptions to this, such as prog() which returns nil unless you call the return() function within to indicate the return value, but I'm less keep on arbitrary jumps out of the middle of a block of code because it's harder to follow, as Lawrence said (it's "spaghetti programming").

You might want to take a look at my video: Writing Good SKILL Code (Video)

By the way, LISP is one of the oldest high level languages, and whilst old has been quite innovative over the years and has influenced a lot of other languages (there are quite a few concepts in Python that originate from LISP, for example).

So yes, I agree - it's quite different from C/C++, Python and Tcl, but then again Python and Tcl are quite different from C/C++ too!

Andrew.