match Statement

[stvowi]

Dear Fabonicci, please compare the implementation of your matcht Statement with the implementation in PHP.

I find the underscore for the default case not so good and we should use the keyword 'default'.

Please think also to TTS-Models.
Then you could have the source code read aloud in the editor and you can better think about it.

[fibodevy]

Both spellings already exist. _ is the wildcard, else is the no-match fallback, and otherwise is a synonym of else. So if you dislike the underscore, write else or otherwise and you get exactly what default would give you. Adding default would be a third spelling of something that is already there twice.

There is a reason _ is not just cosmetic sugar for else. _ is a pattern, not a clause, and it goes where a clause cannot:

match p of
  (0, _): writeln('on Y axis');
  (_, 0): writeln('on X axis');
  'w', 'a', _: writeln('w, a, or anything else');
end;

Inside a tuple pattern _ means "ignore this field", and it can also close a comma-separated pattern list. default has no meaning in either position. The two constructs are not interchangeable, they just happen to overlap in the simple case where the wildcard sits alone in the last branch.

They also differ in match all, where every matching branch runs. A _: branch is a branch, so it always executes. else is a fallback and runs only when no branch matched at all. Collapsing them into one keyword would lose that distinction.

One more practical point: _ costs nothing. It is not a reserved word, the parser only treats it specially in pattern position, so existing code that uses _ as an identifier keeps working. default is a different story, it is already taken in Pascal for property defaults and for Default(T), and overloading it as a control-flow keyword would be confusing.

On the PHP comparison: PHP match is expression-only, compares with ===, throws on no match, and has no patterns beyond plain values, so default is the only thing it needs. Here match is both a statement and an expression, supports ranges, comma lists, tuple patterns, a subject-less boolean form and match all, so a real wildcard pattern earns its place.

[stvowi]

Ok - thanks for the answer.

[stvowi]

Your match statement sparked my curiosity about Unleashed Pascal.