# Function subtypes
**URL:** https://discourse.julialang.org/t/function-subtypes/92292
**Category:** General Usage
**Created:** [December 29, 2022, 9:11pm UTC](https://discourse.julialang.org/t/function-subtypes/92292 "2022-12-29T21:11:30Z")
**Posts on this page:** 2
**Page:** 3
### Author:  [@nchisholm](https://discourse.julialang.org/u/nchisholm)
#### Post date: [January 17, 2023, 8:05pm UTC](https://discourse.julialang.org/t/function-subtypes/92292/42 "2023-01-17T20:05:42Z")
Hmm… 🤔. How about leaving things more like your original macro:
```julia
abstract type MyAbstractType end
@singleton foo isa MyAbstractType
```
where the `@singleton` expands to
```julia
struct var"#foo" <: MyAbstractType end
const foo = var"#foo"()
```
Then it would be just a matter adjusting `Base.show` methods to nicely pretty-print things depending on whether the singleton instance `isa Function` or not.
```julia
julia> foo
foo (singleton)
julia> typeof(foo) # internally var"#foo", but that's transparent to the user
typeof(foo)
julia> abstract type MyFuncType <: Function end
julia> @singleton bar <: MyFuncType
bar (generic function with 0 methods)
julia> typeof(bar) # internally var"#bar"
typeof(bar)
```
This would not require any change to the language itself—only a new macro and adjustment of `Base.show`.
---
### Author:  [@dylanxyz](https://discourse.julialang.org/u/dylanxyz)
#### Post date: [January 17, 2023, 8:38pm UTC](https://discourse.julialang.org/t/function-subtypes/92292/43 "2023-01-17T20:38:08Z")
You’re right. A macro makes more sense. I’m gonna edit my original answer (where the macro is defined) to use `isa` instead of `<:`, which i also think its better, and omit the `Base.show` definition.
[Previous page](https://discourse.julialang.org/t/function-subtypes/92292.md?page=2)