Run sequence of commands on trigger?

[nathanrboyer]

How can I load a package and then define some constants?

This is working great!
(StucturalUnits.jl reexports Unitful.jl and exports inch.)

["@u_str", "Unitful", "inch"] => :(@usingany StructuralUnits),

julia> x = 2inch
2 inch

But I want more units available by default, and this is not working.

["@u_str", "Unitful", "inch", "mm", "psi"] => :(@usingany StructuralUnits; const mm=u"mm"; const psi=u"psi"),

julia> x = 2mm
┌ Info: Failed to run `begin
│     #= C:\Users\nboyer.AIP\.julia\config\startup.jl:43 =# @usingany StructuralUnits
│     #= C:\Users\nboyer.AIP\.julia\config\startup.jl:43 =#
│     const mm = u"mm"
│     #= C:\Users\nboyer.AIP\.julia\config\startup.jl:43 =#
│     const psi = u"psi"
│ end`
│   exception =
│    LoadError: UndefVarError: `@u_str` not defined in `Main`
│    Suggestion: check for spelling errors or missing imports.
└    in expression starting at C:\Users\nboyer.AIP\.julia\config\startup.jl:43
ERROR: UndefVarError: `mm` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Stacktrace:
 [1] top-level scope
   @ REPL[1]:1
 [2] top-level scope
   @ none:1

[LilithHafner]

Ah. This is an evaluation order issue. You can reproduce it without this package like so:

julia> begin
           using Unitful
           const mm = u"mm"
       end
ERROR: LoadError: UndefVarError: `@u_str` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
in expression starting at REPL[1]:3

The issue is that the macros are expanded first (erroring) and then (if macros expand successfully) the code is executed and Unitful is loaded. A general solution here is using @eval which delays macro expansion of its body until runtime.

julia> begin
           using Unitful
           @eval const mm = u"mm"
       end
mm

In the case of BasicAutoloads

["@u_str", "Unitful", "inch", "mm", "psi"] => :(@usingany StructuralUnits; @eval(const mm=u"mm"; const psi=u"psi")),

You could also do something like using StructuralUnits.Unitful: mm or any other construct that does not rely on Unitful being loaded at macro-expansion time.

[nathanrboyer]

Perfect, thank you! Sorry for it being unrelated.

[LilithHafner]

Happy to help!