> no special syntax for anything.
(list '(1. . #\#)
-5/6+7.s-8i
`(1 ,@2)
1@1 ;hmmm, no unquote splicing comma ;-)
10# ;surprised?
(list #i+1 +1i 1+i) ;complicated or complex?
#e-1e10i ;Old MacDonald?
"(* 9 10)" #())
Yeah - the number syntax is pretty cool.
So `#e0.1` is exact 0.1 which means it will be read as an exact fraction 1/10 and `#i0.1` will be read as a floating point number.The `i` in `8i` is the imaginary unit. The `1@1` is the polar notation for complex numbers.
The `10#` is a compatibility remain (the Scheme authors wanted a way to see how many signifant digits were known. In `10#` there 2. So `#` stands for "some digit". In most implementations this is read as 0. More details at [1]
An `#` followed by a list datum is read as a vector. Thus `#()` is an empty vector and `()` is an empty list.
[1] https://stackoverflow.com/a/10936403/23567
Complicated? Well, to support both inexact (floating point) and exact numbers (bignums and fractions) it makes sense to have `#i` and `#e` to explicitl choose. The default is (more or less): numbers with . are inexact the others are exact.
At first I was frustrated by this comment, having a fair amount of Lisp experience failing to grok the examples. In less than one minute I was able to locate, download and install the latest Racket and was in a REPL. There really are no excuses.
This was a wild ride. I'm torn on whether this feels like the Reader is bloated/polluted or whether this is the coolest numerical parser I've ever used. You can really do a lot to coerce the these numbers just by inserting an {o,s,e,i,b,#} into the number, with different semantics depending on the position of the character.
Somewhat overwhelming, I can only hope there's some elegance underlying it all...
You forgot hash table and regular expression literals.
It looks like Racket nerfed the shared-structure / "Datum Labels" for circular lists and the like (I see it is still in section 2.4 of r7rs):
...and I should have included `#|block comments|#`, datum `#;comments`, and probably `|symbols with spaces|`.That has been in Racket for a long time.
I tried:
...over athttps://onecompiler.com/racket
...and it didn't compile, complaining:
...maybe there is a switch needed to enable it?I am not 100% sure what's going on, but you can use `read` mode this way:
I think the problem is that `read` / `write` support shared data constructed using `shared`. But programs (read by `read-syntax` are not allow to have cycles.Curious, how would look that in Python?
It looks more like a "program" for an HP15c pocket scientific calculator.
Not necessarily a bad thing but also not exactly what I would call "expressive".
You may be able to build anything you want --- which may be efficient when communicating with the machine. But I wonder about now well this would communicate with other programmers.
It's not a program, it is (obviously) a totally unrealistic hodgepodge expression for a list of constant values that simply demonstrates the literal syntax for a variety of types of values (real numbers, dotted pairs, rational numbers, complex numbers, polar coordinates, etc. -- Racket is unusually expressive in the types of literals). Your comment demonstrates something typical of HN, and it's not a good thing. It's as if in a discussion about C someone posted, without explanation, an entry from the Obfuscated C contest and then someone else, making zero effort to understand what was posted, said that it looked like line noise and questioned whether C is conducive to communication between programmers.