How do I substitute symbols in a language object?

Question

Suppose I have the following language object:

lang <- quote( f(x=a) )

and I want to substitute in 1 for a. How

Answer 1

You can use substituteDirect rather than substitute:

substituteDirect(lang, list(a=1))

Eventually you may be able to use substitute. According to ?substituteDirect:

The goal is to replace this with an eval= argument to substitute.