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?

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

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^{<small>IV</small>}, 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.