Discussion: Porting 58000 lines of D and C++ to jai, Part 0: Why and How

[FeepingCreature]

On Thursday, 24 November 2022 at 12:04:27 UTC, FeepingCreature 
wrote:
> For instance, this is valid code:
>
>     import std.stdio;
>     void switchtest(int i, bool b)
>     {
>         switch (i)
>         {
>             case 1:
>                 if (b)
>                 {
>                     case 2:
>                         writefln!"Case 1b or 2: %s, %s"(i, b);
>                         return;
>                 }
>                 break;
>             default: break;
>         }
>         assert(false);
>     }
>
>     void main()
>     {
>         switchtest(1, true);
>         switchtest(2, false);
>     }

Ie. to explain what's happening here:

The syntax tree structure of `if/else` is `if (EXPRESSION) 
STATEMENT [else STATEMENT]`. `static foreach` does not match 
`else`, so it fails to parse.

The syntax tree structure of `switch/case` is not, as you would 
expect, `switch (EXPRESSION) { [case EXPRESSION: STATEMENT*]* }`.

Instead, it's `switch (EXPRESSION) STATEMENT` and `STATEMENT = 
... | CASE_STATEMENT`, `CASE_STATEMENT = case EXPRESSION:`, where 
the CASE_STATEMENT is *semantically* (not syntactically) verified 
to occur inside `switch`, with no other restrictions on their 
placement. That's the only reason it works with `static foreach`.

(All parse rules made up from memory, not taken from the spec.)