cmdstanr depends R >= 4.1

[jsocolar]

If we try to install cmdstanr on old R versions, we get (here the code says jsocolar instead of stan-dev but I'm on a fresh pull of master)

> remotes::install_github("jsocolar/cmdstanr")
Downloading GitHub repo jsocolar/cmdstanr@HEAD
── R CMD build ───────────────────────────────────────────────────────────────────────────────────────────────
✔  checking for file ‘/tmp/RtmpFkMY9G/remotes1b3f49de2ec6/jsocolar-cmdstanr-a787764/DESCRIPTION’ ...
─  preparing ‘cmdstanr’:
✔  checking DESCRIPTION meta-information ...
─  checking for LF line-endings in source and make files and shell scripts
─  checking for empty or unneeded directories
─  building ‘cmdstanr_0.5.3.tar.gz’
   
Installing package into ‘/home/ec2-user/R/x86_64-koji-linux-gnu-library/4.0’
(as ‘lib’ is unspecified)
* installing *source* package ‘cmdstanr’ ...
** using staged installation
** R
Error in parse(outFile) : 
  /tmp/RtmpkwuvBf/R.INSTALL52123e8a5d25/cmdstanr/R/fit.R:1450:23: unexpected input
1449:     log_lik_i_upars <- function(x, upars, i, parameter_name = "log_lik", ...) {
1450:       apply(upars, 1, \
                            ^
ERROR: unable to collate and parse R files for package ‘cmdstanr’
* removing ‘/home/ec2-user/R/x86_64-koji-linux-gnu-library/4.0/cmdstanr’
Warning message:
In i.p(...) :
  installation of package ‘/tmp/RtmpFkMY9G/file1b3f7c22c84a/cmdstanr_0.5.3.tar.gz’ had non-zero exit status

To fix, we either need to revert from \ to function or we need to depend on R >= 4.1.0. Happy to make either fix depending on what you want.

[rok-cesnovar]

Yeah, we need to revert from \ to function. Its not worth to bump the minimal R version just for this. Thanks for spotting this!!