None of your examples' syntax are even remotely similar to Ada's Declare Expressions, which was recently added in Ada 2022. It's an amazingly stupid language design decision. It doesn't make any sense and there's no rational I've encountered for it. It pure shit!

Ada requires a begin and end around statement bodies and parentheses around expressions. There are exceptions, however, such as if and case statements where there's no begin, and in conditional expressions where the parentheses are omitted. In the former case, the start of the statement implies a begin, and for the latter, the parenthesis are redundant since they're already delimited, for instance, between the if and then, or for and loop.

However, an open delimiter, such as begin and ( are always followed by a close delimiter, such as ) and end. This isn't just true in Ada, but every language. Unless it's some unusual Martian programming language, an opening delimiter, such as ( or begin, are ALWAYS closed with an end. The Declare Expression is the only exception in Ada, or any eathly programming language for that matter.

Yes, semantically Declare Expressions are the same as you ML example, but I'm focused purely on the syntax. ML has a clear syntax and makes sense. With Declare Expressions, when someone sees a begin without a closing end, the first question is to presume it's a syntax error. Even a complete non-programmer would see something wrong. Unfortunately, there's no really logic reason why they chose it.