• 9il (27/27) Jan 30 2022 [mir.algebraic](http://mir-core.libmir.org/mir_algebraic.html)
• 9il (19/20) Jan 30 2022 I like `suit` a lot. It helps to define very clean visitors.
• SealabJaster (20/21) Jan 30 2022 Nice work!
• SealabJaster (30/33) Jan 30 2022 I missed the full example I wanted to give:

9il <ilyayaroshenko gmail.com> writes:

[mir.algebraic](http://mir-core.libmir.org/mir_algebraic.html) 
additions:
  - `some`, `none`, and `suit` second level algebraic visitor 
handlers
  - ` reflectErr` UDA
  - `Err` auto expanded wrapper when ` reflectErr` can't be used
  - Required utility API

```d
import mir.algebraic;
import mir.conv: to;

alias orElse(alias fun) = visit!(some!"a", none!fun);
alias convertErrToString = orElse!(to!string);

// can be any other type including integer enums
 reflectErr
static struct ErrorInfo {
     string msg;
     auto toString() const { return msg; }
}

alias V = Variant!(Err!string, ErrorInfo, long, double);
alias R = typeof(convertErrToString(V.init));

static assert(is(R == Variant!(string, long, double)), 
R.stringof);
assert(convertErrToString(V(1)) == 1);
assert(convertErrToString(V(1.0)) == 1.0);
assert(convertErrToString(ErrorInfo("b")) == "b");
assert(convertErrToString("Ш".err) == "Ш");
```

9il <ilyayaroshenko gmail.com> writes:

On Sunday, 30 January 2022 at 10:58:33 UTC, 9il wrote:
 [mir.algebraic](http://mir-core.libmir.org/mir_algebraic.html)

I like `suit` a lot. It helps to define very clean visitors.

```d
import std.traits: isDynamicArray, Unqual;
import std.meta: templateNot;
alias V = Variant!(long, int, string, long[], int[]);
alias autoGetElementType = match!(
     (string s) => "string", // we override the suit handler below 
for string
     suit!(isDynamicArray, a => Unqual!(typeof(a[0])).stringof),
     suit!(templateNot!isDynamicArray, a => 
Unqual!(typeof(a)).stringof),
);
assert(autoGetElementType(V(string.init)) == "string");
assert(autoGetElementType(V((long[]).init)) == "long");
assert(autoGetElementType(V((int[]).init)) == "int");
assert(autoGetElementType(V(long.init)) == "long");
assert(autoGetElementType(V(int.init)) == "int");
```

SealabJaster <sealabjaster gmail.com> writes:

On Sunday, 30 January 2022 at 10:58:33 UTC, 9il wrote:
 ...

Nice work!

Anytime I see things like this it makes me wish D would adopt 
some form of pattern matching.


expressive it can be in certain cases, i.e.:

```fsharp
let (|Seconds|NotANumber|) (str : string) =
     let mutable value = 0.0
     match Double.TryParse(str, &value) with
     | true -> Seconds value
     | false -> NotANumber

...somewhere in an expression/function

        match model.Duration with
        | Seconds s -> ValidRequest {
                 ...omitted
             }
        | NotANumber -> InvalidRequest "Duration is not a valid 
number"
```

SealabJaster <sealabjaster gmail.com> writes:

On Sunday, 30 January 2022 at 16:08:17 UTC, SealabJaster wrote:
 On Sunday, 30 January 2022 at 10:58:33 UTC, 9il wrote:
 ...

 ...

I missed the full example I wanted to give:

```fsharp
let (|Seconds|NotANumber|) (str : string) =
     let mutable value = 0.0
     match Double.TryParse(str, &value) with
     | true -> Seconds value
     | false -> NotANumber

let (|ValidRequest|InvalidRequest|) (model : PutSubModel, rs : 
ResultSet) =
     if model.Taken > DateTimeOffset.UtcNow then
         InvalidRequest "This result was taken in the future?"
     ...
     else
         match model.Duration with
         | Seconds s -> ValidRequest {
                ...
             }
         | NotANumber -> InvalidRequest "Duration is not a valid 
number"

let rec handleModel (model: PutSubModel) (array: PutSubModel[]) =
     match (model, rs) with
     | InvalidRequest error -> Some error
     | ValidRequest req ->
         req |> db.Add |> ignore
         if array.Length = 0 then
             None
         else
             handleModel array.[0] array.[1..]
```