[R] inverse currying

[baptiste auguie]

After some more digging (grep "alist" R-devel/ ), I've come up with this,

tools:::as.alist.symbol("x")

sugar = function(fun, id = "id"){
 ff <- formals(fun)
 if( id %in% names(ff))
   stop(paste(id, "is part of args(fun)"))

 new.arg <- tools:::as.alist.symbol(id)

 formals(fun) <- c(unlist(ff), new.arg)
 fun

}

foo = function(x, a=1){
 x
}

sugar(foo)
sugar(foo, 'a')
sugar(sugar(foo))

sugar(foo, 'my.new.arg')


Best,

baptiste



2009/10/1 baptiste auguie <baptiste.auguie at googlemail.com>:
> Dear list,
>
> I have the following function,
>
> sugar = function(fun, id = "id"){
>  ff <- formals(fun)
>  if( id %in% names(ff))
>    stop("id is part of args(fun)")
>  formals(fun) <- c(unlist(ff), alist(id=))
>  fun
> }
>
> which one may use on a function foo,
>
> foo = function(x){
>  x
> }
>
> sugar(foo) # results in the extended closure,
>
> function (x, id)
> {
>    x
> }
>
> Its limitation (other than not working with .Primitives) is the 'id'
> tag that I add in the formals of fun(). I don't know how to create a
> alist(id=) pairlist where id can be changed. I tried the usual bquote
> and substitute approach but they don't seem to work here. I suppose I
> could do something like,
>
> parse(text = paste("alist(",id, "=)", sep=""))
>
> but this is usually not recommended.
>
> Any ideas?
>
> Best regards,
>
> baptiste
>