Strange error when sum_type macro is used inside a begin block #67

Tortar · 2024-01-22T02:16:42Z

For non-parametric sum types this works fine

julia> using SumTypes

julia> begin
           mutable struct A
               x::Int
           end
           @sum_type B begin
               C(a::A)
           end
       end

but when you try with a parametric one a strange error with no informative stacktrace appears:

julia> using SumTypes

julia> begin
           mutable struct A{X}
               x::X
           end
           @sum_type B{X} begin
               C{X}(a::A{X})
           end
       end
ERROR: syntax: SlotNumber objects should not occur in an AST
Stacktrace:
 [1] top-level scope
   @ REPL[2]:1
 [2] top-level scope
   @ REPL[2]:5

Tortar · 2024-01-22T02:19:58Z

This works fine instead

julia> using SumTypes

julia> begin
           mutable struct A{Y}
               x::Y
           end
           @sum_type B{X} begin
               C{X}(a::A{X})
           end
       end

so the workaround is simple, but I'm puzzled by what Julia gets confused

MasonProtter · 2024-01-22T12:31:12Z

I'm guessing this is because SumTypes emits an Expr(:toplevel, ...) object instead of an Expr(:block, ...) for the struct definition. There's some kinda scary edge cases with macros defining structs, but since the implementation of sumtypes has changed a lot, maybe we no longer need to use Expr(:toplevel) and can go back to Expr(:block).

Here's a MWE:

julia> macro foo()
           ex = :(struct Foo{X}; x::X end)
           esc(Expr(:toplevel, ex))
       end
@foo (macro with 1 method)

julia> begin
           mutable struct A{X}
               x::X
           end
           @foo
       end
ERROR: syntax: SlotNumber objects should not occur in an AST
Stacktrace:
 [1] top-level scope
   @ REPL[7]:1
 [2] top-level scope
   @ REPL[7]:5

MasonProtter mentioned this issue Jan 22, 2024

remove unnecessary usage of Expr(:toplevel) #69

Merged

MasonProtter closed this as completed in #69 Jan 22, 2024

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Strange error when sum_type macro is used inside a begin block #67

Strange error when sum_type macro is used inside a begin block #67

Tortar commented Jan 22, 2024 •

edited

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Tortar commented Jan 22, 2024

MasonProtter commented Jan 22, 2024 •

edited

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Strange error when sum_type macro is used inside a begin block #67

Strange error when sum_type macro is used inside a begin block #67

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Tortar commented Jan 22, 2024 • edited Loading

Tortar commented Jan 22, 2024

MasonProtter commented Jan 22, 2024 • edited Loading

Tortar commented Jan 22, 2024 •

edited

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MasonProtter commented Jan 22, 2024 •

edited

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