LOGO-L> map, high-level functions

[neuwirth <neuwirth@smc.univie.ac.at>]

this is already quoted twice,
so i don't know who originally said it.

> >I also think someone should tackle understanding list
> >manipulation (primarily a lesson in recursion) before
> >moving into high level list manipulation functions
> >such as MAP and friends. Excluding the turtle graphics
> >recursive list processing is the HEART of Logo.

i would like to disagree

especially map is an example which one can think of 
"nonrecursively" and gain something.

the standard approach, if one had to implement map,
of course would be linear recursion.
that in a certain sense is sequential linear thinking.

but map is the prototype of something which can be executed in 
parallel. if you have many computers and all know your code,
each of them can execute one of the function calls and then you 
can collect the results of this parallel executions and
combine the "result list"

if you still are in "linear recursion thinking mode",
you don't see the parallel paradigm in map.

the other important high level function which leads to
parallel algorithms is reduce.

if the underlying 2 argument function is associative,
it can be implemented in a parallel way which is much faster
than the standard linear recursion solution.

i think i said something to that extent already some months 
ago.

if parallel computing is an important paradigm which should be 
taught (and i think it is) we should carefully think
about primitives which lead to parallel computation in a 
natural way.


--
Erich Neuwirth <neuwirth@smc.univie.ac.at>
Computer Supported Didactics Working Group, Univ. Vienna
Visit our SunSITE at http://sunsite.univie.ac.at



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