[erlang-questions] extend parser to allow single quotes in variable names (or: "let's confuse the text editors!")

Richard O'Keefe <>
Sun Oct 7 23:44:45 CEST 2012


On 8/10/2012, at 5:35 AM, Motiejus Jakštys wrote:

> Hi,
> 
> In Haskell you can have variable names with single quotes. Imagine for a
> moment you are in a perfect world:
> 
> oops() ->
>    A = 1024,
>    A' = math:log(A) / math:log(2),
>    io:format("Wow! ~p~n", [A']).
> 
> What would you think about this extension?

I would think it was pointless.

Haskell			Erlang
x			X
x'			X1
x''			X2
x'''			X3
x''''			X4
x'''''			X5

Spot the pattern?

Haskell (or at least GHC) allows primes inside identifiers too,
but nobody seems to take advantage of that.

Consider f'x 'y'.  Want to read _that_ fast?
Consider f'x' y'.  Want to tell them apart fast?

SML also allows primes inside and at the end of identifiers.
This is much less of a pain in SML because SML writes
character literals as #"x" rather than 'x'.

There is historically and in good typography a clearly visible
distinction between the apostrophe and the superscript I II III
IV V: (x' is x prime; x'' is x second; x''' is x third, and
the next one is x<sup><small>IV</small></sup>, x fourth, not
x'''').  It's only the limitations of old typewriters and ASCII
that lead us to confuse them.  Superscript Roman numerals in
Unicode identifiers, fine; using the apostrophe as the quote
character for atoms and also in identifiers, not fine.




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