> There seems to be a misundertanding. I do not want to describe how but
> why. I.e. why does
> f(s):=s[1] not work as expected?
You can do so, but my belief is that few people care about why.
They only want to get something to work. (that is, how.)
Furthermore, they don't want to read manuals or explanations.
Often they will learn from random trials or maybe by reading examples.
The learn-by-example is the (very successful) theory behind the 1,000 page
books that have titles like "Excel for Dummies".
The learn-from-random-trials is the theory that a well-designed language or
interface will be so natural that people will use it correctly without
needing an explanation. An example of this approach in the mathematical
computation domain is the Macintosh Graphing Calculation by Ron Avitzur,
also see www.nucalc.com for a version for windows, also.
It is natural for academics, to believe in rational logical explanations.
They tend to thrive on more abstract "symbolic" reasoning. Most people, even
mathematicians, do better with visual metaphors.
My tilu web site does symbolic integrals. There have been about 300,000
visits. The link to the instructions is essentially unused.
RJF