R help - Oct 2025 - Construct a function with argments specified by an R expression

Define the names and a prototype and then use formals(f) <- ... as shown.

  # inputs
  arg_names <- c("x", "y", paste0("a", 1:3),
paste0("b", 1:3))
  f <- function() {}

  arg <- alist(x = )
  formals(f) <- setNames(c(arg, rep(arg, length(arg_names)-1)), arg_names)
  f

giving

  function (x, y, a1, a2, a3, b1, b2, b3)
  {
  }

On Fri, Oct 24, 2025 at 10:23?PM Rolf Turner <rolfturner at posteo.net>
wrote:
>
>
> I want to build a function (say "buildFn") to *return* a function
of the
> form
>
>     foo(x,y,a1, ... an, b1, ..., bn)
>
> where the arguments ai and bi are given in the form of a list created
> in R.  E.g. I'd like to be able to say
>
>      argnms <-
c(paste0("a",1:3),paste0("b",1:3"))
>      foo <- buildFn(argnms)
>
> with the resulting "foo" having arguments x, y, a1, a2, a3, b1,
b2, b3.
>
> I thought I might be able to do this using "formals<-" but I
cannot get
> this to work.  i could provide more detail of what I've tried, but
it's
> probably not worth it.
>
> Can anyone steer me in the right direction?  Thanks.
>
> cheers,
>
> Rolf Turner
>
> --
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Stats. Dep't. (secretaries) phone:
>          +64-9-373-7599 ext. 89622
> Home phone: +64-9-480-4619
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

This can be simplified slightly to

  # inputs
  arg_names <- c("x", "y", paste0("a", 1:3),
paste0("b", 1:3))
  f <- function() {}

  arg <- alist(x = )
  formals(f) <- setNames(rep(arg, length(arg_names)), arg_names)
  f

  ## function (x, y, a1, a2, a3, b1, b2, b3)
  ## {
  ## }

On Sun, Oct 26, 2025 at 10:41?AM Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
>
> Define the names and a prototype and then use formals(f) <- ... as
shown.
>
>   # inputs
>   arg_names <- c("x", "y", paste0("a",
1:3), paste0("b", 1:3))
>   f <- function() {}
>
>   arg <- alist(x = )
>   formals(f) <- setNames(c(arg, rep(arg, length(arg_names)-1)),
arg_names)
>   f
>
> giving
>
>   function (x, y, a1, a2, a3, b1, b2, b3)
>   {
>   }
>
> On Fri, Oct 24, 2025 at 10:23?PM Rolf Turner <rolfturner at
posteo.net> wrote:
> >
> >
> > I want to build a function (say "buildFn") to *return* a
function of the
> > form
> >
> >     foo(x,y,a1, ... an, b1, ..., bn)
> >
> > where the arguments ai and bi are given in the form of a list created
> > in R.  E.g. I'd like to be able to say
> >
> >      argnms <-
c(paste0("a",1:3),paste0("b",1:3"))
> >      foo <- buildFn(argnms)
> >
> > with the resulting "foo" having arguments x, y, a1, a2, a3,
b1, b2, b3.
> >
> > I thought I might be able to do this using "formals<-"
but I cannot get
> > this to work.  i could provide more detail of what I've tried, but
it's
> > probably not worth it.
> >
> > Can anyone steer me in the right direction?  Thanks.
> >
> > cheers,
> >
> > Rolf Turner
> >
> > --
> > Honorary Research Fellow
> > Department of Statistics
> > University of Auckland
> > Stats. Dep't. (secretaries) phone:
> >          +64-9-373-7599 ext. 89622
> > Home phone: +64-9-480-4619
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
https://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com


-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com