# Simple is better than complex

**URL:** <https://discourse.julialang.org/t/simple-is-better-than-complex/18821>\
**Category:** General Usage\
**Tags:** question, proposal\
**Created:** [December 19, 2018, 6:06am UTC](https://discourse.julialang.org/t/simple-is-better-than-complex/18821 "2018-12-19T06:06:47Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![Sukera](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@Sukera](https://discourse.julialang.org/u/Sukera)\
**Post date:** [December 19, 2018, 6:19am UTC](https://discourse.julialang.org/t/simple-is-better-than-complex/18821/2 "2018-12-19T06:19:10Z")

</div>

Please search this forum and the issues on github - there has been A LOT of discussion about this, for example these threads

> [@Another possible solution to the global scope debacle](https://discourse.julialang.org/t/another-possible-solution-to-the-global-scope-debacle/15894):
>
> The infamous issue [https://github.com/JuliaLang/julia/issues/28789](https://github.com/JuliaLang/julia/issues/28789) has been on most of our minds for a while now. Although I’ve stopped posting there, I can tell you I’ve been thinking about it a lot, as have Stefan and Jameson and others, and we have continued discussing it off and on. We should really try to get it right. Last time around, we more-or-less settled on changing only the REPL, which has the main advantage of being non-breaking for most code. But after sleeping on it, it does not …

> [@New scope solution](https://discourse.julialang.org/t/new-scope-solution/16707):
>
> I have an alternate, non-breaking solution to the scope issue previously discussed on [discourse](https://discourse.julialang.org/t/another-possible-solution-to-the-global-scope-debacle/15894) and [github](https://github.com/JuliaLang/julia/issues/28789). The new potential solution is the following rule to decide whether a variable, x, which is not marked as explicitly local or glogal and which is assigned to in a top-level scope construct is local or global: x is global if it is accessed before being assigned on all paths through the scope body. In other words, x is local unless there’s no way it could make sense for it to be local. Or…

> <https://github.com/JuliaLang/julia/issues/28789>
>
> \### Example 1
> 
> This came up with a student who upgraded from 0.6 to 1.0 direct…ly, so never even got a chance to see a deprecation warning, let alone find an explanation for new behavior:
> 
> \`\`\`julia
> julia\> beforefor = true
> true
> 
> julia\> for i in 1:2
> beforefor = false
> end
> 
> julia\> beforefor # this is surprising bit
> true
> 
> julia\> beforeif = true
> true
> 
> julia\> if 1 == 1
> beforeif = false
> end
> false
> 
> julia\> beforeif # Another surprise!
> false
> 
> julia\> function foo()
> infunc = true
> for i in 1:10
> infunc = false
> end
> @show infunc
> end
> foo (generic function with 1 method)
> 
> julia\> foo() # "I don't get this"
> infunc = false 
> \`\`\`
> 
> \### Example 2
> 
> \`\`\`julia
> julia\> total\_lines = 0
> 0
> 
> julia\> list\_of\_files = \["a", "b", "c"\]
> 3-element Array{String,1}:
> "a"
> "b"
> "c"
> 
> julia\> for file in list\_of\_files
> # fake read file
> lines\_in\_file = 5
> total\_lines += lines\_in\_file
> end
> ERROR: UndefVarError: total\_lines not defined
> Stacktrace:
> \[1\] top-level scope at ./REPL\[3\]:4 \[inlined\]
> \[2\] top-level scope at ./none:0
> 
> julia\> total\_lines # This crushs the students willingness to learn
> 0
> \`\`\`
> 
> I "get" why this happens in the sense that I think I can explain, with sufficient reference to the arcana in the manual about what introduces scopes and what doesn't, but I think that this is problematic for interactive use.
> 
> In example one, you get a silent failure. In example two, you get an error message that is very there-is-no-spoon. Thats roughly comparable to some Python code I wrote in a notebook at work today.
> 
> I'm not sure what the rules are in Python, but I do know that generally you can't assign to things at the global scope without invoking global. But at the REPL it does work, presumably because at the REPL the rules are different or the same logic as if they were all are in the scope of function is applied.
> 
> I can't language-lawyer the rules enough to propose the concrete change I would like, and based on Slack this isn't even necessarily perceived as an issue by some people, so I don't know where to go with this except to flag it.
> 
> Cross-refs:
> \#19324
> https://discourse.julialang.org/t/repl-and-for-loops-scope-behavior-change/13514
> https://stackoverflow.com/questions/51930537/scope-of-variables-in-julia

And plenty of others.

---

_[View the full topic](https://discourse.julialang.org/t/simple-is-better-than-complex/18821)._