Re: DSSSL side effect-freeness

[Harald Hanche-Olsen <hanche+dsssl-l@xxxxxxxxxxxx>]

- "G. Ken Holman" <gkholman@xxxxxxxxxxxxxx>:

| At 14:06 98/01/27 +0900, Frank A. Christoph wrote:
| >It seems very odd to me that a language which has been so
| >conscientiously purged of side effects is nevertheless call-by-value.
| 
| But wouldn't it be necessary to be call-by-value?  Call-by-reference
| would (I think) blatantly allow potential side effects.  If the
| calling routine called a subroutine using call-by-reference, then
| the subroutine could have incredible side effects on the variable
| being passed.

Only if the language had primitives for mutating whatever is
referenced, which the DSSSL language doesn't.  And without such
primitives, I don't see that there is any difference, from the point
of view of the programmer, between call-by-value and
call-by-reference!  In fact, in the absence of side-effects, the
implementor is free to use call-by-reference if he so wishes, and he
might well wish to for efficiency reasons.  Only he might not call it
call-by-reference, but rather think of it as there being no need to
duplicate information that is not going to be mutated anyway.  Or,
since calling the same procedure twice with the same arguments in the
same context will always yield the same result, the implementor is
free to cache results and simply return the cached result the next
time around.

| [...] but as I said above, I'm not a language theorist

Neither am I.  Pretty soon now, some such is going to come out of the
woods and shoot both our arguments to pieces.  Such is life.

- Harald


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