[R] glm families in R

[Francisco Cribari]

Is the following difference between S+ and R normal or is it a bug? 
Thanks. FC. 

PS: S+ 4.5 for Windows and R 0.63.1 for Windows. 

S-PLUS output:

> inverse.gaussian()$deriv
> function(mu)
> -2/mu^3
 
R output:

> inverse.gaussian()$deriv
> NULL
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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