call_modify: Modify the arguments of a call.
In lazyeval: Lazy (Non-Standard) Evaluation

Modify the arguments of a call.

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call_modify(call, new_args, env = parent.frame())

call_standardise(call, env = parent.frame())

`call`	A call to modify. It is first standardised with `call_standardise`.
`new_args`	A named list of expressions (constants, names or calls) used to modify the call. Use `NULL` to remove arguments.
`env`	Environment in which to look up call value.

call <- quote(mean(x, na.rm = TRUE))
call_standardise(call)

# Modify an existing argument
call_modify(call, list(na.rm = FALSE))
call_modify(call, list(x = quote(y)))

# Remove an argument
call_modify(call, list(na.rm = NULL))

# Add a new argument
call_modify(call, list(trim = 0.1))

# Add an explicit missing argument
call_modify(call, list(na.rm = quote(expr = )))