# How to write a recursive macro?
**URL:** https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652
**Category:** General Usage
**Created:** [July 22, 2022, 8:12pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652 "2022-07-22T20:12:56Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@greatpet](https://discourse.julialang.org/u/greatpet)
#### Post date: [July 22, 2022, 8:12pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/1 "2022-07-22T20:12:56Z")
I came across some online posts about implementing short-circuiting logical operators as macros in Lisp, and I’m wondering how to do the same in Julia. I’m trying to write a vararg macro `@or` such that
```julia
@or expr1 expr2 expr3 expr4
```
expands into
```julia
if expr1
true
else
@or expr2 expr3 expr4
end
```
The recursion should end when there is only one argument, i.e.
```julia
@or expr1
```
should expand into simply `expr1`.
I made some attempts but got confused about how to interpolate vararg tuples in `quote` expressions. Any ideas?
---
### Author:  [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)
#### Post date: [July 22, 2022, 8:38pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/2 "2022-07-22T20:38:40Z")
This is not recursive, however it seems to do what you want.
```julia
ior(x,y) = x || y
macro or(xs...)
:(foldl(ior, $xs, init=false))
end
```
```julia
julia> @or(false), @or(true)
(false, true)
julia> @or(false, false), @or(true, true)
(false, true)
julia> @or(true, false), @or(false,true)
(true, true)
```
---
### Author:  [@greatpet](https://discourse.julialang.org/u/greatpet)
#### Post date: [July 22, 2022, 8:44pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/3 "2022-07-22T20:44:44Z")
Thanks, but I was actually trying to avoid the built-in `||` operator and re-implement it using only the if-else clause, just for fun, following this [Stack Overflow Post](https://stackoverflow.com/a/24843965/3623956) in Lisp.
---
### Author:  [@jules](https://discourse.julialang.org/u/jules)
#### Post date: [July 22, 2022, 8:54pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/4 "2022-07-22T20:54:45Z")
Like this?
```julia
macro or(args...)
length(args) == 1 && return only(args)
quote
if $(esc(args[1]))
true
else
@or $(args[2:end]...)
end
end
end
```
```julia
julia> @or 1 == 2 1 == 3 1 == 1
true
julia> @macroexpand @or 1 == 2 1 == 3 1 == 1
quote
#= Untitled-2:150 =#
if 1 == 2
#= Untitled-2:151 =#
true
else
#= Untitled-2:153 =#
begin
#= Untitled-2:150 =#
if 1 == 3
#= Untitled-2:151 =#
true
else
#= Untitled-2:153 =#
1 == 1
end
end
end
end
```
Probably the escaping isn’t quite right 🙂
---
### Author:  [@greatpet](https://discourse.julialang.org/u/greatpet)
#### Post date: [July 22, 2022, 9:08pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/5 "2022-07-22T21:08:06Z")
> [@jules](#):
>
> ```julia
> macro or(args...)
> length(args) == 1 && return only(args)
> quote
> if $(esc(args[1]))
> true
> else
> @or $(args[2:end]...)
> end
> end
> end
>
> ```
That works! A little glitch is that I tried to add `esc` to your `args[2:end]` but that breaks the interpolation. I’ll be very interested if someone knows how to do this.
---
### Author:  [@greatpet](https://discourse.julialang.org/u/greatpet)
#### Post date: [July 22, 2022, 9:42pm UTC](https://discourse.julialang.org/t/how-to-write-a-recursive-macro/84652/6 "2022-07-22T21:42:39Z")
OK, here’s a simple modification of @jules’s code to impose hygiene.
```julia
macro or(args...)
args_esc = esc.(args)
length(args_esc) == 1 && return only(args_esc)
quote
if $(args_esc[1])
true
else
@or $(args_esc[2:end]...)
end
end
end
```