Jons Mostovojs @jonn@social.doma.dev

Polymorphic compare is awfully convenient, but it has serious downsides and should mostly be avoided in production code. To understand why, it helps to understand how polymorphic compare works.

Polymorphic compare operates directly on the runtime representation of #OCaml values, walking the structure of those values without regard for their type.

And despite ignoring types, it mostly behaves as you would hope. Comparisons on ints and floats respect the ordinary ordering of numeric values, and containers like strings, lists, and arrays are compared lexicographically. And it works on almost every OCaml type, with some important exceptions like functions.

But the type-oblivious nature of polymorphic compare means that it peeks under ordinary abstraction boundaries, and that can lead to some deeply confusing results. Maps themselves provide a great example of this. Consider the following two maps.

let m1 = Map.of_alist_exn (module Int) [1, "one";2, "two"];;
val m1 : (int, string, Int.comparator_witness) Map.t = <abstr>
let m2 = Map.of_alist_exn (module Int) [2, "two";1, "one"];;
val m2 : (int, string, Int.comparator_witness) Map.t = <abstr>

OCaml

Logically, these two maps should be equal, and that’s the result that you get if you call Map.equal on them:

Map.equal String.equal m1 m2;;
- : bool = true

OCaml

But because the elements were added in different orders, the layout of the trees underlying the maps will be different. As such, polymorphic compare will conclude that they’re different.

We can see this below. Note that Base hides polymorphic comparison by default, but it is available within the Poly module.

Poly.(m1 = m2);;
Exception: Invalid_argument "compare: functional value".

OCaml
This comparison failed because polymorphic compare doesn’t work on functions, and maps store the comparison function they were created with. Happily, there’s a function,
https://dev.realworldocaml.org/maps-and-hashtables.html

Many people do not understand why I think that the IEEE 754 Floating Point standard is defective and should be replaced.

So I made a demonstrator. You can enter a number literal or arithmetic expression, and it will show you IEEE 754's version. I think the errors are shocking.

https://www.crockford.com/deconstruct.html

The moment when #Odesa yesterday was hit with a #Iskander missile armed with a cluster munitions warhead.

Metal fragments were found as far as 1,5km from the impact site according to the Prosecutor General's Office.

https://t.me/suspilnenews/32032

#Ukraine #Russia

As per the post of @ose_rouge goes: also today the #JewishBrigades and their sympathizers could not take part in the yearly commemoration of liberation from fascism in #Milan #Milano today without extra security. These attacks against the Brigades from #ProPalestine organizations have a inglorious tradition. https://www.juedische-allgemeine.de/juedische-welt/streit-um-die-resistenza/

Oh and by the way

a similar attempt to rewrite the history is coming from the right

They oppose antifascism

I don't condone that one either

again we know history

just because we despise the revisionist attempts form the communists we don't condone the revisionist attempts from the fascists

on april 25th Italy calebrates the liberation from the nazifascism

usually, demonstrations take place all around the country, the largest ones in Rome and Milan

The partisans who fought the fascists were of all the political spectrum

They were catholics, socialists, communists, liberals, even monarchists

In the republican era, the communist part tried to rewrite the history

since many years they have contested the participation of the Jewish Brigade to the demonstrations in Milan and Rome because of antizionism/antisemitism

This year too

The Jewish Brigade fought the fascist under the UK flag

There are tens of thousand of dead US and British soldiers on th emilitary cemeteries in Italy

This is what liberation was all about

You propal, proputin, proassad, protrump are just revisionists

We know history, you won't rewrite it

https://en.wikipedia.org/wiki/Jewish_Brigade