Make Julia’s Error Codes Even Better Than Elm’s

Internals & Design
3

Maybe we can start by reading that post and looking at examples of Julia’s errors and considering how they could be more beginner-friendly.

xs = [1,2,3]
xs[0]

% julia tmp.jl      
ERROR: LoadError: BoundsError: attempt to access 3-element Vector{Int64} at index [0]
Stacktrace:
 [1] getindex(A::Vector{Int64}, i1::Int64)
   @ Base ./array.jl:861
 [2] top-level scope
   @ /tmp/tmp.uyTu9zl540/tmp.jl:2
in expression starting at /tmp/tmp.uyTu9zl540/tmp.jl:2

Rewriting the error:

1 | xs = [1,2,3]
2 | xs[0] 
    ^^^^^

I tried to access a Vector{Int64} at index [0] but the valid indexes are 
[1], [2], [3].

The stack of function calls, from latest to earliest, was:
 [1] getindex(A::Vector{Int64}, i1::Int64)
   @ Base ./array.jl:861
 [2] top-level scope
   @ /tmp/tmp.uyTu9zl540/tmp.jl:2
  • arrows point at the location in the code, with context. Does julia currently have the ability to isolate code spans so that the ^^^^ arrows can work?
  • the valid indexes are mentioned
  • uses full sentences
  • uses “I” for the compiler, which does have a more relatable tone IMHO
  • doesn’t introduce “stacktrace” jargon
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