[racket] Racketrivia: Using ' as an identifier suffix

That's a scary convention. It's hard for humans to see the difference!

On Thu, Jan 8, 2015 at 2:32 PM, Jon Zeppieri <zeppieri at gmail.com> wrote:
> You can use the unicode prime character (′) as a suffix. In DrRacket,
> you can type that as \prime followed by ctrl-\. It would be a lot
> nicer to map it to a simple key combo like λ is,
>
> -Jon
>
>
> On Thu, Jan 8, 2015 at 3:15 PM, Greg Hendershott
> <greghendershott at gmail.com> wrote:
>> So Haskell conventionally uses ' as a suffix, prime. From what I've
>> seen, Scheme and Racket tend to use * instead.
>>
>> At some point I "learned" that you cannot use ' as a suffix in Racket.
>>
>> Today I tried again, and was surprised to see that it works... somewhat.
>>
>> $ racket
>> Welcome to Racket v6.1.1.6.
>> -> (define x' 42)
>> -> x'
>> 42
>> -> (+ x' 10)
>> '(+ x '10)
>> -> (+ 10 x')
>> ; readline-input:4:8: read: unexpected `)'
>> -> (+ 10 x' )
>> ; readline-input:5:8: read: unexpected `)'
>>
>>
>> 0. It turns out x' _is_ a valid identifier, and it self-evaluates just
>> fine. Interesting.
>>
>> 1. I don't understand why (+ x' 10) evaluates not to 52, and not even
>> an error, but... '(+ x '10).  WAT.
>>
>> 2. Less surprising to me is that (+ 10 x') and even (+ 10 x' ) are
>> errors. But actually, I wonder why the reader (or lexer?) couldn't
>> handle ' followed by a character that can't be part of an identifier?
>>
>>
>> p.s. I'm not proposing this would be a great suffix style to use.
>> Quick, distinguish x' from 'x ! And don't type one when you mean the
>> other! I get that. Even so, I'm curious.
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