🚀 go-pugleaf

In article <MYltLT200VsiM0U3Yx@andrew.cmu.edu> gb17+@andrew.cmu.edu (George Thomas Baggott) writes:
>In a truly functional language (i.e. no side effects at all), a function
>for altering a large data structure (adding an entry to a dictionary,
>for example) would be written as:
>
>	dictionary_add(dictionary, entry) returns dictionary;
>	/* return a copy of dictionary with entry added to it */
>
>This is very costly, however.  If side effects were allowed, you could
>do it at a much smaller cost:
>
>	dictionary_add(dictionary, entry);
>	/* add entry to dictionary */
>
>Is there some way to have a language with no side effects, yet still be
>able to solve this class of problems in a practical way?  If not what is
>the minimum amount of comprimise that must be made?
>
>
>George

Single assignment semantics requires that an aggregate value be copied
if one wishes to modify an element of the value.  However, an
implementatiion may observe the last use of a value and update it in place.

We have done this for SISAL with good results, although there are still
instances where recognition does not take place.  

A Postscript version of David Cann's Ph.D. dissertation with all the
gory detail on this subject is available via anonymous ftp from
handel.CS.ColoState.EDU (129.82.102.16).  See file TR.89-108.ps in the
directory ~ftp/pub/SISAL.



Rod Oldehoeft                    Email: rro@CS.ColoState.EDU
Computer Science Department      Voice: 303/491-5792
Colorado State University        Fax:   303/491-2293
Fort Collins, CO  80523