Re: Overloaded logic operators

m.helvensteijn@gmail.com> wrote
>> (Being able to write if a<b<c is neat though and I've just added
>> that to my language, with about 5 lines of code; it just converts to
>> if (a<b) and (b<c).)
>
> Yes, chained comparison is neat. But watch out. If someone wrote: (a <
> b() < c), he would expect b() to only be evaluated once, not twice.
> This makes a big difference if b() has side-effects. Also, the syntax
> can be extended to mixed comparison operators. For example: (a < b = c
> < d).
>
> Did you catch all that in 5 lines of code? Then I admire your code
> modularity. :-)


No; someone mentioned about evaluating b twice, and I fixed it for when b is
an assignment:


a < (b:=x) < c


becomes: 'a < (b:=x) and b < c'. It just means that the user has to create
an explicit copy by writing (b:=x) instead of just x, when x has side
effects.


That took another 5 or 6 lines. This is all just syntax after all.


And yes the original 5 lines did deal with all six relational operators, and
could cope (by an accident of recursion) with long chains such as a<b<c<d<e.


--
Bartc

Return to the comp.compilers page.
Search the comp.compilers archives again.