On Tue, Nov 16, 2010 at 12:27 PM, Serge Le Huitouze <serge.lehuitouze@gmail.com> wrote:
It seems that there is no predefined function to test an "'a option" for being
specifically "None" or "Some _". This seems to be confirmed by the very
existence of:
http://ocaml-lib.sourceforge.net/doc/Option.html
which defines such functions ("is_none" and "is_some").
I found it weird to be forced to use "match" expressions in my code for
doing that, e.g.:
* let curSelectedRow = ref None in
* let updateButtonsStatus () =
* button_remove#misc#set_sensitive
* (match !curSelectedRow with None -> false | _ -> true)
* in
* ...
Though useless in this case (just use ((<>) None)), there is a very nice syntax extension proposal by Richard Jones to transform any pattern into a boolean predicate : (matches p) would be equivalent to a function that returns true if the input matches the pattern. I have implemented it in camlp4 (the code may be slightly bitrotten) in case you're interested:
I'm not familiar with operators and their precedence, but I wonder: is it
possible to do something similar with OCaml?
In OCaml, the associativity/precedence of an operator is defined by its first symbols. For example (++$*) has exactly the precedence of (+). You can find all precedence classes and their prefixes in the OCaml Manual:
Though this is less flexible that other languages that let you choose precedence and associativity on a case per case basis, it gives a nice homogeneity to binary operators: you don't need to look at the operator definition site to have a (vague, unless you know the table by hearth) idea of its syntactic properties.