On Tue, Nov 16, 2010 at 12:27 PM, Serge Le Huitouze < serge.lehuito...@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: http://bluestorm.info/camlp4/pa_matches.ml.html > 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: http://caml.inria.fr/pub/docs/manual-ocaml/expr.ht...@manual.kwd33 <http://caml.inria.fr/pub/docs/manual-ocaml/expr.ht...@manual.kwd33>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.
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