# Mod not defined for two identical irrationals
**URL:** https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153
**Category:** General Usage
**Tags:** question
**Created:** [April 4, 2018, 11:25am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153 "2018-04-04T11:25:07Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@mvhulten](https://discourse.julialang.org/u/mvhulten)
#### Post date: [April 4, 2018, 11:25am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/1 "2018-04-04T11:25:08Z")
```julia
julia> mod(π,ℯ)
0.423310825130748
julia> mod(√2,π)
1.4142135623730951
julia> mod(π,π)
ERROR: mod not defined for Irrational{:π}
Stacktrace:
[1] error(::String, ::String, ::Type) at ./error.jl:42
[2] no_op_err at ./promotion.jl:420 [inlined]
[3] mod(::Irrational{:π}, ::Irrational{:π}) at ./promotion.jl:440
[4] top-level scope
julia> versioninfo()
Julia Version 0.7.0-DEV.3686
...
```
Two identical irrational numbers don’t parse well by `mod()`. Is this a bug or by design?
---
### Author:  [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)
#### Post date: [April 4, 2018, 11:29am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/2 "2018-04-04T11:29:30Z")
Just to give a reason for why this happens (without commenting on if this is a bug or by design).
```julia
julia> typeof(promote(π, ℯ))
Tuple{Float64,Float64}
julia> typeof(promote(π, π))
Tuple{Irrational{:π},Irrational{:π}}
```
So in the first case we will call the `mod` function with the irrationals converted to floats, but not in the second.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [April 4, 2018, 11:37am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/3 "2018-04-04T11:37:37Z")
Perhaps something like
```julia
Base.mod(::Irrational{T}, ::Irrational{T}) where T = 0
```
& related could be used to cover this corner case.
---
### Author:  [@mvhulten](https://discourse.julialang.org/u/mvhulten)
#### Post date: [April 4, 2018, 11:46am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/4 "2018-04-04T11:46:44Z")
Thanks for the explanation. I don’t know if a corner case must be introduced, but of course I was expecting `mod(π,π)==0`.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [April 4, 2018, 11:49am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/5 "2018-04-04T11:49:49Z")
I must be missing something, but I thought `mod(x,x)` should be `0`.
---
### Author:  [@mvhulten](https://discourse.julialang.org/u/mvhulten)
#### Post date: [April 4, 2018, 11:50am UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/6 "2018-04-04T11:50:52Z")
Of course! Fixed 🙂
---
### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [April 4, 2018, 3:18pm UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/7 "2018-04-04T15:18:14Z")
This would make a nice small feature addition pull request.
---
### Author:  [@simonbyrne](https://discourse.julialang.org/u/simonbyrne)
#### Post date: [April 4, 2018, 4:17pm UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/8 "2018-04-04T16:17:22Z")
Yes, please open an issue!
---
### Author:  [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)
#### Post date: [April 4, 2018, 6:56pm UTC](https://discourse.julialang.org/t/mod-not-defined-for-two-identical-irrationals/10153/9 "2018-04-04T18:56:35Z")
opened: [https://github.com/JuliaLang/julia/issues/26701](https://github.com/JuliaLang/julia/issues/26701)