Lists of language objects

[wlandau]

Summary

What is the best way to create a list of language objects in vctrs?

vctrs::list_of(quote(foo <- 0L))
#> `list(...)[[1]]` must be a vector, not a call
utils::packageDescription("vctrs")$RemoteSha
#> [1] "25d8607960881c74d1d9272eb71580140311c00d"

^{Created on 2019-05-06 by the reprex package (v0.2.1)}

Session info

devtools::session_info()
#> ─ Session info ──────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.5.2 (2018-12-20)
#>  os       Red Hat Enterprise Linux    
#>  system   x86_64, linux-gnu           
#>  ui       X11                         
#>  language (EN)                        
#>  collate  en_US.UTF-8                 
#>  ctype    en_US.UTF-8                 
#>  tz       America/Indiana/Indianapolis
#>  date     2019-05-06                  
#> 
#> ─ Packages ──────────────────────────────────────────────────────────────
#>  package     * version    date       lib source                      
#>  assertthat    0.2.1      2019-03-21 [1] CRAN (R 3.5.2)              
#>  backports     1.1.4      2019-04-10 [1] CRAN (R 3.5.2)              
#>  callr         3.2.0      2019-03-15 [1] CRAN (R 3.5.2)              
#>  cli           1.1.0      2019-03-19 [1] CRAN (R 3.5.2)              
#>  crayon        1.3.4      2017-09-16 [2] CRAN (R 3.5.2)              
#>  desc          1.2.0      2018-05-01 [2] CRAN (R 3.5.2)              
#>  devtools      2.0.2      2019-04-08 [1] CRAN (R 3.5.2)              
#>  digest        0.6.18     2018-10-10 [2] CRAN (R 3.5.2)              
#>  evaluate      0.13       2019-02-12 [1] CRAN (R 3.5.2)              
#>  fs            1.2.7      2019-03-19 [1] CRAN (R 3.5.2)              
#>  glue          1.3.1      2019-03-12 [1] CRAN (R 3.5.2)              
#>  highr         0.8        2019-03-20 [1] CRAN (R 3.5.2)              
#>  htmltools     0.3.6      2017-04-28 [2] CRAN (R 3.5.2)              
#>  knitr         1.22       2019-03-08 [1] CRAN (R 3.5.2)              
#>  magrittr      1.5        2014-11-22 [2] CRAN (R 3.5.2)              
#>  memoise       1.1.0      2017-04-21 [2] CRAN (R 3.5.2)              
#>  pkgbuild      1.0.3      2019-03-20 [1] CRAN (R 3.5.2)              
#>  pkgload       1.0.2      2018-10-29 [2] CRAN (R 3.5.2)              
#>  prettyunits   1.0.2      2015-07-13 [2] CRAN (R 3.5.2)              
#>  processx      3.3.0      2019-03-10 [1] CRAN (R 3.5.2)              
#>  ps            1.3.0      2018-12-21 [1] CRAN (R 3.5.2)              
#>  R6            2.4.0      2019-02-14 [1] CRAN (R 3.5.2)              
#>  Rcpp          1.0.1      2019-03-17 [1] CRAN (R 3.5.2)              
#>  remotes       2.0.4      2019-04-10 [1] CRAN (R 3.5.2)              
#>  rlang         0.3.4.9003 2019-05-06 [1] Github (r-lib/rlang@6a232c0)
#>  rmarkdown     1.12       2019-03-14 [1] CRAN (R 3.5.2)              
#>  rprojroot     1.3-2      2018-01-03 [2] CRAN (R 3.5.2)              
#>  sessioninfo   1.1.1      2018-11-05 [2] CRAN (R 3.5.2)              
#>  stringi       1.4.3      2019-03-12 [1] CRAN (R 3.5.2)              
#>  stringr       1.4.0      2019-02-10 [1] CRAN (R 3.5.2)              
#>  testthat      2.1.1      2019-04-23 [1] CRAN (R 3.5.2)              
#>  usethis       1.5.0      2019-04-07 [1] CRAN (R 3.5.2)              
#>  vctrs         0.1.0.9003 2019-05-06 [1] Github (r-lib/vctrs@25d8607)
#>  withr         2.1.2      2018-03-15 [2] CRAN (R 3.5.2)              
#>  xfun          0.6        2019-04-02 [1] CRAN (R 3.5.2)              
#>  yaml          2.2.0      2018-07-25 [2] CRAN (R 3.5.2)              
#>  zeallot       0.1.0      2018-01-28 [1] CRAN (R 3.5.2)              
#> 
#> [1] /home/c240390/.R/library
#> [2] /opt/R/R-3.5.2/lib64/R/library

Motivation

Lists of language objects come into play at ropensci/drake#489 (comment) and r-lib/pillar#34 (comment). drake in particular makes heavy use of tibbles with lists of language objects, and it would be great to have non-hacky pretty printing.

[hadley]

list_of() is not designed to support lists of non-vectors. vctrs is about vectors, not non-vectors, so you'll need to use something else.