Matchbox and CMD CHECK

Ok, first, the package I wrote about yesterday will be called matchbox, following Dmytro Perepolkin’s suggestion (thanks!). You can get it at GitHub.

There isn’t much to it yet since I haven’t really started implementing the data structures I want to put in it. I plan to implement most of the structures from Function Data Structures in R but using pattern matching and tail-recursion optimisation, and I will write about it here.

I have implemented some linked-lists functions, but a CMD CHECK of the package fails.

If I run the functions through tailr, I get this interesting Note:

Error in attr(e, "srcref")[[i]] : subscript out of bounds
Calls: <Anonymous> ... <Anonymous> -> collectUsage -> collectUsageFun -> walkCode -> h
Execution halted
llength: Error while checking: subscript out of bounds
llrev: Error while checking: subscript out of bounds

I have no idea what is happening here.

If I disable the tail-recursion optimisation, I get this Note:

llength: no visible global function definition for ‘llength<-’
llength: no visible binding for global variable ‘car’
llrev: no visible global function definition for ‘llrev<-’
llrev: no visible binding for global variable ‘car’
Undefined global functions or variables:
  car llength<- llrev<-

This, I am pretty sure, is because of the pattern matching DSL in pmatch. The llength function, for example, is define like this:

llength <- function(llist, acc = 0) {
    pmatch::cases(
        llist,
        NIL -> acc,
        CONS(car, cdr) -> llength(cdr, acc + 1)
    )
}

and the cases syntax uses the assignment operator. Therefore, the check thinks we are using the replacement operator length<-. The

CONS(car, cdr) -> llength(cdr, acc + 1)

expression is translated into

llength(cdr, acc + 1) <- CONS(car, cdr)

by the parser, and a function call on the left-hand side of an assignment is interpreted as a replacement operator. So here, at least, I think I understand the problem. I just don’t know how to tell the package check that I know what I am doing and it shouldn’t worry about it.

Help!?