# A most harrowing collection of Julia WATs
**URL:** https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323
**Category:** General Usage
**Tags:** wat
**Created:** [March 2, 2022, 6:15pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323 "2022-03-02T18:15:32Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@miguelraz](https://discourse.julialang.org/u/miguelraz)
#### Post date: [March 2, 2022, 6:15pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/1 "2022-03-02T18:15:33Z")
Hello all! đ
Iâve been collecting a few of the most cursed corner cases of Julia [WATs](https://www.destroyallsoftware.com/talks/wat) that [I know of here](https://miguelraz.github.io/blog/juliawats/) (WIP), but I would appreciate if people could share their own rare specimens as well.
Please ping me with your contributions and Iâll post with proper credit.
Hereâs an example of what I mean by a Julia WAT:
```julia
julia> e = 9998.0
9998.0
julia> 2e
19996.0
julia> 2e+4
20000.0
julia> 2e+5 # This should be 20001.0, right?
200000.0
julia> 2e + 5 # note the spacing
20001.0
```
âŚwat.
Some of these are just unavoidable corner cases of multiple design constraints, others are an artifact of parsing being hard, but theyâre all supposed to be tongue-in-cheek puzzles of our dear JuliaLang \<3.
---
### Author:  [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)
#### Post date: [March 2, 2022, 6:26pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/2 "2022-03-02T18:26:27Z")
I mean, as a scientist I did not understand the point until the last line, because the `2e+4` immediately was parsed by my mind as a number in scientific notation and I did not understand the relation with the previous `e` or what you did mean by your first comment.
Surely there are some Julia WATs, but this seems kinda expected from any language with both floating points and implicit multiplication, is Julia the only language with these two characteristics?
---
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [March 2, 2022, 6:30pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/3 "2022-03-02T18:30:28Z")
> [@miguelraz](#):
>
> âŚwat.
Interestingly, syntax highlighting makes it hard to understand the wat
---
### Author:  [@lawless-m](https://discourse.julialang.org/u/lawless-m)
#### Post date: [March 2, 2022, 8:14pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/4 "2022-03-02T20:14:52Z")
See also BogumiĹ KamiĹskiâs
[Pitfalls of macro invocation in Julia](https://bkamins.github.io/julialang/2022/01/14/macros.html)
```julia
julia> macro m(args...)
show(args)
end
@m (macro with 1 method)
julia> @m 1 + 1
(:(1 + 1),)
julia> @m 1+1
(:(1 + 1),)
julia> @m 1 +1
(1, 1)
```
---
### Author:  [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)
#### Post date: [March 3, 2022, 4:23am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/5 "2022-03-03T04:23:56Z")
I always thought allowing things like `2x` (instead of requiring `2*x`) was just setting up things to fail in
unexpected ways. Wat!?
---
### Author:  [@Philogicatician](https://discourse.julialang.org/u/Philogicatician)
#### Post date: [March 3, 2022, 7:34am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/6 "2022-03-03T07:34:19Z")
One of your WATs isnât quite true:
---
### Author:  [@Philogicatician](https://discourse.julialang.org/u/Philogicatician)
#### Post date: [March 3, 2022, 7:37am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/7 "2022-03-03T07:37:50Z")
However, the other example of âShadowingâ does reproduce the error shown that Kristopher Carlsson pointed out:
---
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [March 3, 2022, 7:50am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/8 "2022-03-03T07:50:55Z")
Probably because you already used `-` in your session
---
### Author:  [@lawless-m](https://discourse.julialang.org/u/lawless-m)
#### Post date: [March 3, 2022, 10:54am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/9 "2022-03-03T10:54:26Z")
One from many on [another of BogumiĹ KamiĹskiâs blog posts](https://bkamins.github.io/julialang/2021/11/12/so.html)
```julia
julia> isequal(sum([-0.0, -0.0]), sum([-0.0, -0.0], init=0.0))
false
```
---
### Author:  [@Philogicatician](https://discourse.julialang.org/u/Philogicatician)
#### Post date: [March 3, 2022, 7:11pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/10 "2022-03-03T19:11:00Z")
Ah, thanks @giordano, looks like youâre right:
---
### Author:  [@tim.holy](https://discourse.julialang.org/u/tim.holy)
#### Post date: [March 4, 2022, 12:08pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/11 "2022-03-04T12:08:08Z")
Great collection! A couple of comments though:
- âand, or on empty collectionsâ: not spelled out, what is the WAT? Or is it really in reference to the âbroadcasting shenanigansâ below it?
- âwhat is this syntax?â Iâm not sure whatâs wrong with it.
```julia
julia> f = function(x) x+1 end
#11 (generic function with 1 method)
julia> f(3)
4
```
Itâs just a way to declare an anonymous functionâIMO itâs an elegant syntax because it makes it very clear that what youâre doing is not assigning a name to the function.
---
### Author:  [@Seif\_Shebl](https://discourse.julialang.org/u/Seif_Shebl)
#### Post date: [March 4, 2022, 12:41pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/12 "2022-03-04T12:41:01Z")
That looks perfectly fine to me, no surprise if it behaves like arrays.
---
### Author:  [@Seif\_Shebl](https://discourse.julialang.org/u/Seif_Shebl)
#### Post date: [March 4, 2022, 12:44pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/13 "2022-03-04T12:44:52Z")
This is well documented in `?isequal`
```julia
..
julia> 0.0 == -0.0
true
julia> isequal(0.0, -0.0)
false
..
```
---
### Author:  [@BeastyBlacksmith](https://discourse.julialang.org/u/BeastyBlacksmith)
#### Post date: [March 4, 2022, 12:54pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/14 "2022-03-04T12:54:19Z")
Another one for the shadowing category
```julia
julia> Iterators = (map = (f, x)->f.(x).^2,)
(map = var"#1#2"(),)
julia> Iterators.map(identity, 1:5)
5-element Vector{Int64}:
1
4
9
16
25
```
Itâs a bit contrived, but actually happened to me in a different way because I accidentily pasted a compat requirement into the REPLâŚ
---
### Author:  [@suavesito](https://discourse.julialang.org/u/suavesito)
#### Post date: [March 4, 2022, 6:10pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/15 "2022-03-04T18:10:30Z")
For me it was that I thought that the anonymous function syntax was only valid using `->`, so this came as a surprise.
Looking at it, I also like it too now đ
```julia
julia> const a = (function(x)
# more code
x^2
end)(2)
4
julia> const b = ((x) -> begin
# more code
x^2
end)(2)
4
```
It is more readable for in-place functions (although I donât know if people use them, maybe for some initializer).
---
### Author:  [@miguelraz](https://discourse.julialang.org/u/miguelraz)
#### Post date: [March 4, 2022, 8:06pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/16 "2022-03-04T20:06:40Z")
Thanks for the comments @tim.holy !
Yes, those comments are basically `TODOs` that I pepper in my blogposts and as I come back to them I overwrite them - perhaps the big đ§ WIP đ§ signs should be a bit more prominent.
And although I agree with your comments on the anonymous function syntax - it definitely made me say âWAT? You can do that?â when I first saw it, so Iâm guessing itâs gonna punk other people too on their first encounter.
---
### Author:  [@schnetter](https://discourse.julialang.org/u/schnetter)
#### Post date: [March 5, 2022, 4:42pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/17 "2022-03-05T16:42:44Z")
Miguel
This code is inefficient when called with an integer argument:
```nohighlight
function f(x)
x += 1
x /= 2
return x
end
```
To make it efficient, use different names for the temporary variables:
```nohighlight
function f(x)
y = x+1
z = y/2
return z
end
```
You see the source of the inefficiency with `@code_warntype`.
-erik
---
### Author:  [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)
#### Post date: [March 5, 2022, 6:54pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/18 "2022-03-05T18:54:05Z")
Infers just fine on 1.7:
```julia
julia> function f(x)
x += 1
x /= 2
return x
end
f (generic function with 1 method)
julia> @code_typed f(1)
CodeInfo(
1 â %1 = Base.add_int(x@_2, 1)::Int64
â %2 = Base.sitofp(Float64, %1)::Float64
â %3 = Base.div_float(%2, 2.0)::Float64
âââ return %3
) => Float64
```
To explain: `@code_warntype` isnât telling the whole truth here, since the optimizer can actually deal with this when lowering slots to phi nodes.
---
### Author:  [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)
#### Post date: [March 5, 2022, 11:40pm UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/19 "2022-03-05T23:40:31Z")
This post was temporarily hidden by the community for possibly being off-topic, unfocused, inappropriate, or spammy.
---
### Author:  [@krasi\_sabyata](https://discourse.julialang.org/u/krasi_sabyata)
#### Post date: [March 7, 2022, 3:16am UTC](https://discourse.julialang.org/t/a-most-harrowing-collection-of-julia-wats/77323/20 "2022-03-07T03:16:24Z")
The floating point example feels expected for me (probably not to someone who is newer to writing code) but the rest of it is very interesting! Thank you for the linked post, its helpful as I get more acquainted with the Julia programming language.
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