[R] list of interdependent functions

[Thomas Petzoldt]

Hello,

I discussed the following problem on the great useR conference with
several people and wonder if someone of you knows a more elegant (or
more common ?) solution than the one below.

The problem:
============

I have several sets of interrelated functions which should be compared.
The functions themselves have different structure, application-specific
names (for readability) and they should be exchangeable. I want to avoid
to construct a generic for every new function, but the functions should
be aggregated together in a common data structure (e.g. list "eq" or an
S4 instance) *and* it should be able for them to "see" and call each
other with too many $ or @. These functions are used in another function
(called "solver" here) which may be used to prepare something before the
call to f2.

The example and a possible solution (which uses an environment
manipulating function "putInEnv()") is given below.

Thanks a lot

Thomas


##======================================================
## An example
##======================================================

## a small list of functions
eq <- list(
  f1 = function(x, K) K - x,
  f2 = function(x, r, K) r * x * f1(x, K)
)

## a solver fnction which calls them
solverB <- function(eq) {
  eq <- putInEnv(eq, environment()) # that's the trick
  f1(3,4) + f2(1,2,3)
 }

## and the final call (e.g. from the command line)
solverB(eq)


##======================================================
## One possible solution. Is there a better one???
##======================================================


putInEnv <- function(eq, e) {
  ## clone, very important to avoid "interferences"!!!
  eq <- as.list(unlist(eq))
  lapply(eq, "environment<-", e)
  nn <- names(eq)
  for (i in 1:length(eq)) {
    assign(nn[i], eq[[i]], envir = e)
  }
  eq
 }