Dissuade from doing assignments inside a call to a function

Functions.Rmd

@@ -567,6 +567,8 @@ A promise has three components:
     y
     ```
 
+    Note that doing the above is generally considered bad style since – due to the nature of lazy evaluation – there is no guarantee that the argument will ever be evaluated and hence the assignment may never take place.[^off-doc-argeval]
+
 *   A value, which is computed and cached the first time a promise is 
     accessed when the expression is evaluated in the specified environment.
     This ensures that the promise is evaluated at most once, and is why you
@@ -587,6 +589,7 @@ A promise has three components:
 
 You cannot manipulate promises with R code. Promises are like a quantum state: any attempt to inspect them with R code will force an immediate evaluation, making the promise disappear. Later, in Section \@ref(quosures), you'll learn about quosures, which convert promises into an R object where you can easily inspect the expression and the environment.
 
+[^off-doc-argeval]: See [chapter 4.3.3 _Argument evaluation_](https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Argument-evaluation) of the official R language definition for some more information about the topic.
 
 ### Default arguments
 \index{functions!default values}