if doesn’t add much imo (I prefer case) and the implicit else clause is not obvious to newcomers.
I would also remove the restriction that string keys must precede atom keys in map literals. i.e.
iex> %{"a" => 1, b: 1}
%{"a" => 1}
iex> %{a: 1, "b" => 1}
** (SyntaxError) iex:3: syntax error before: "b"
For a beginner this can be a bit of a wtf moment! 
iex(1)> %{:a => 1, "b" => 1}
%{:a => 1, "b" => 1}
Probably just me, but I like to stay consistent in any given line and use only either the “atom: value” style or “key => value” style for any one declaration / usage .. which neatly side-steps that oddity .. which is, as you note … odd. heh.
yes A data type for rational numbers. It would be best if in code divisions got put straight to this type. I believe clojure does this
3
# %Rational{numerator: 3, divisor:1}
2/3
# %Rational{numerator: 3, divisor:1}
Then a number protocol to get decimal values
Number.to_string(1 + 3/2, decimal_places: 2)
# 2.50
Number.to_string(1 + 2/3, decimal_places: 2)
# 1.67
As a protocol it would be extensible to other structs
Number.to_string(%SquareRoot{value: 2}, decimal_places: 2)
# 1.41
Number.to_string(%Pi{}, decimal_places: 2)
# 3.14
+1 for rationals over floats. And maybe a fixed-decimal type. I remember exactly one instance where I needed floating point calculations in the last 2 decades (conversion of Dutch grid coordinates to WGS84 for a mapping application where we had postal code geocoding in the one and the map in the other), countless of times where rational or fixed-decimal type were asked for and I could start my ticket by converting the old (floating-point and thus error prone for money) code to something better fitting.
IMO floating point is the most overrated and unnecessary datatype in our industry. Unless you work in science, or maybe engineering? But that seems to me a vanishing minority, let them include specific libraries.
Yep, it’s because of the legacy of who used, and therefore drove, the technology decisions in past decades.
Ok, so now that I understand the ideas you have in mind (sorry for the many questions earlier; just so many different things one might mean by “no floats”) .. yeah, I bet a lot of people would find a decimal / rational number type far more useful and less surprising.
Keeping floats as a special type would certainly be enough for those who truly need them …
nice idea 
Yes, I tend to feel that mixing atoms/strings in a map is a code smell in any case. But the ordering issue definitely contradicts the priinciple of least astonishment!
I would think for science you would be most keen to avoid floats. scientific results would definitely want to be more specific about their errors.
I think it should be possible to implement something like this within Elixir Macro’s. I hope to find the time to try eventually. One of the best features is using elixir macro’s to test features which can eventually be a future direction for the language.
I completely forgot but I would also remove with after my macro experiments with alternatives
They may be useful for newcomers so we don’t get a kneejerk “wait, no if statement?” reaction.
There’s a whole field of study called Numerical Analysis that deals with the problem of using floating point to solve engineering equations. Floats aren’t a problem if you understand the limitations and use of precision.
For science the input data almost always has some level of fuziness or imprecision, so learning to deal with that in an appropriate way makes sense. Floating point was designed by scientists to do science. It’s a reasonable compromise between accuracy and speed.
Even today, for large science computations speed and memory use are primary constraints on the kind of science you can do. Having 10 digits of precision in the results is generally not the primary constraint.
And yes, I am very biased as I have spent 30+ years helping scientists get floating point “right” in one way and another.
