“Identity element” section with an explanation and a table of Raku ops

[AlexDaniel]

See https://en.wikipedia.org/wiki/Identity_element.

I think this should be discussed in Perl 6 docs (not just linked to wikipedia). We can have a similar table that specifically lists perl 6 ops.

For example, identity element for ~ is an empty string (""), even though ~ can be used for Blobs. There's a separate trap for that particular detail (see #2124), but it should be discussed in main docs also in context of identity elements (or maybe reduction).

[JJ]

Maybe include it in the Math document? It's a mathematical concept, after all...

[JJ]

There are 71 messages in the thread about identity operators: https://groups.google.com/forum/#!topic/perl.perl6.language/YIWdmJ54buw
I'm checking out the source, and it's almost impossible to find out which are the identity operators unless you go source by source. Let me see if I can find a compromise, at least with some operators.

[AlexDaniel]

I don't like the table as it is confusing and doesn't answer the question for some ops.

For example, what about × (multiplication)? It says 0 for “Arithmetic” but the identity for × is 1.

What about //? Or ∘? And so on.

I think the table should list all operators, maybe group them if you like. I don't think there's necessarily a need to check the source code as you can just do say […] and it'll give you the identity op in most cases. Also we should probably have a test file in roast that checks identities of all ops (if we don't have it already, please create it).

[mykhal]

At its current state, the section is quite informative.

For now, I see a couple of issues in the table:

• Bool::True for Equality should probably be just True, for consistency
• junctions are not mentioned, [&], [|], [^] # => (all(), any(), one())

.. as @AlexDaniel mentioned, e.g. [o] has also interesting result.

[coke]

Updated the Bool::True item - Someone needs to verify that the junction and o items are spec or "only" rakudo's implementation.