Andrei Alexandrescu:

Just read the slides, very interesting.

There are many papers, books and articles around that explain the same things, but that explanation is easy to understand even for people not used to functional programming (as I still partially am).

I think it would be interesting to experiment with an Expected!T that holds an Algebraic!(T, Exception) as state,

In those slides as other member of the sum type they have used an enumeration of possible error conditions (or at first even just strings of the error messages), sometimes augmented with more information, like:

| EmailNotValid of EmailAddress
| DbAuthorizationError of ConnectionString * Credentials
| SmtpTimeout of SmtpConnection
| SmtpBadRecipient of EmailAddress

template bind(alias fun) { ... }

such that given a function e.g.

int fun(string a, double b);

bind!fun is this function:

Expected!int bind!fun(Expected!string a, Expected!double b) {
  if (a.sux || b.sux) return composeExceptions(a, b);
  return fun(a.rox, b.rox);

There would also be bindNothrow:

Expected!int bindNothrow!fun(Expected!string a, Expected!double b) {
  if (a.sux || b.sux) return composeExceptions(a, b);
  try return fun(a.rox, b.rox);
  catch (Exception e) return e;

One of the main points of using those two railways is to avoid exceptions.

but of course built-in tuple syntax and basic forms of pattern matching in switch ( ) improve the syntax and make the code more handy, handy enough to push more D
programmers in using it.

No :o).

Are you saying you don't want built-in tuples and that you also don't agree with the proposal in issue 596 and that you don't agree that a better syntax doesn't make monads like those actually handy to use? I don't understand what's controversial in what I have written there.

From a syntax point of view issue 596 asks for an optional onMatch method, and if you want a syntax to create variables in switch cases. Plus support for structs and classes as variables to switch on.

The use of Algebraic, Nullable and Expected is very different (and safer) if you use them through pattern matching. The point is not to ape the functional languages: currently in D Nullable is not much safer (and not more handy) than using a null pointer.


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