# Interesting problem with where parameters
**URL:** https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824
**Category:** General Usage
**Created:** [December 19, 2018, 11:00am UTC](https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824 "2018-12-19T11:00:48Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Qiyamah](https://discourse.julialang.org/u/Qiyamah)
#### Post date: [December 19, 2018, 11:00am UTC](https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824/1 "2018-12-19T11:00:48Z")
I have the following code:
```nohighlight
abstract type TypedFun end
abstract type ReturnFun{R} <: TypedFun end
abstract type NoArgFun{R} <: ReturnFun{R} end
abstract type FullFun{Tuple,R} <: ReturnFun{R} end
#single argument function
struct SAFun{T,R} <: FullFun{Tuple{T},R}
fn::Function
end
(⇒)(::Type{T}, ::Type{R}) where {T,R} = SAFun{T, R}
(⇒)(::Nothing, ::Type{R}) where {R} = NoArgFun{R}
struct MM{T}
x::T
end
f(fun::(Any ⇒ MM{T})) where T = fun(3)
```
the function f definition gives the following error
ERROR: UndefVarError: R not defined
However this doesn’t give the same error:
```nohighlight
f(fun::(Any ⇒ MM)) = fun(3)
```
Why is this happening…
Thanks, and how can I fix it?
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [December 19, 2018, 11:04am UTC](https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824/2 "2018-12-19T11:04:11Z")
Please provide a **self-contained** example. We don’t know what `SAFun` is and you are not providing a stack trace.
> [@Please read: make it easier to help you](https://discourse.julialang.org/t/psa-make-it-easier-to-help-you/14757):
>
> Welcome to the Julia Discourse! We are enthusiastic about helping Julia programmers, both beginner and experienced. This public service announcement (PSA) outlines best practices when asking for help. Following these points makes it easier for us to help you and more likely you’ll get a prompt, useful answer. Keywords are highlighted to make it easier to refer to specific points. Choose a descriptive title that captures the key part of your question, eg “plots with multiple axes” instead of …
---
### Author:  [@mauro3](https://discourse.julialang.org/u/mauro3)
#### Post date: [December 19, 2018, 11:13am UTC](https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824/3 "2018-12-19T11:13:39Z")
This works `f(fun::(Any ⇒ MM{T} where T)) = fun(3)`. Note though that the `Any ⇒ MM{T} where T` part is evaluated at function definition and not later. Thus having the `where` outside does not make sense.
---
### Author:  [@Qiyamah](https://discourse.julialang.org/u/Qiyamah)
#### Post date: [December 19, 2018, 7:51pm UTC](https://discourse.julialang.org/t/interesting-problem-with-where-parameters/18824/4 "2018-12-19T19:51:57Z")
what if the same T is used in other parameters of the function such as
f(x::T, fun::(Any ⇒ MM{T})) where T = fun(x)
how do we fix this?