ignoreIndexRanges argument for FORLOOP

[kenkellner]

Adds an ignoreIndexRanges argument to the FORLOOP macro. You can provide a list of index ranges to the argument and they will be ignored when constructing the loop. For example:

x[1:n] <- FORLOOP(sum(y[1:n, 1:3]), ignoreIndexRanges = list(quote(1:3)))

will return

for (i in 1:n){
  x[i] <- sum(y[i, 1:3])
}

Because the FORLOOP macro, for flexibility reasons, doesn't use the use3pieces or unpackArgs arguments to buildMacro, the implementation of this argument is a bit clunky. The line of code with the macro call goes into the macro function as one undifferentiated line of quoted code, so we need to extract and evaluate the content of the argument

nimbleMacros/R/FORLOOP.R

Line 34 in e5972be

ignore <- eval(code[[length(code)]]$ignoreIndexRanges, envir = .env)

and then remove it from the line of code so the rest of it can be processed

nimbleMacros/R/FORLOOP.R

Line 38 in e5972be

code[[length(code)]]$ignoreIndexRanges <- NULL

Fixes #41