We may wonder how Julia parses code when functions are nested. We can pick a simple example here that takes the sine of x+1 and then takes the cosine of the result. The abstract syntax tree is shown as follows:

Here, we can clearly see the tree structure. The outermost function, cos, contains a single argument, which is an expression node with a call to the sin function. This expression in turn contains a single argument, which is another expression node with a call to the + operator function with two arguments—the x variable and a value of 1. Now, let's continue with our work on expressions.