alternate syntax for functionals using tags

gistfile1.txt

``` r
#################################################
# DEFINE TAGS / TAG ADVERBS USING PACKAGE {tag} #
#################################################

# remotes::install_github("moodymudskipper/tag")
mapping_impl <- tag::tag(
  args = alist(.pmap =),
  {
    # setup
    call <- match.call()
    f    <- call[[c(1,3)]]
    args <- as.list(call[-1])
    # prefix detection
    is_prefixed <- function(x) {
      is.call(x) && 
        identical(x[[1]], quote(`!`)) && 
        is.call(x[[2]]) && 
        identical(x[[2]][[1]], quote(`?`))
    }
    prefixed_lgl <- sapply(args, is_prefixed)
    # remove prefix from args
    args[prefixed_lgl] <- lapply(args[prefixed_lgl], `[[`,c(2,2))
    
    # build pmap call, feed prefixed args to the .l argument, and the rest to the `...`
    list_call <- as.call(c(quote(list),args[prefixed_lgl]))
    pmap_call <- as.call(c(.pmap, list_call, f, args[!prefixed_lgl]))
    # run in appropriate environment
    eval.parent(pmap_call)
  })

# define tag adverbs, with aliases
mapping     <- m     <- mapping_impl(quote(purrr::pmap))
mapping_chr <- m_chr <- mapping_impl(quote(purrr::pmap_chr))
mapping_dbl <- m_dbl <- mapping_impl(quote(purrr::pmap_dbl))
mapping_dfr <- m_dfr <- mapping_impl(quote(purrr::pmap_dfr))
mapping_dfc <- m_dfc <- mapping_impl(quote(purrr::pmap_dfc))
mapping_int <- m_int <- mapping_impl(quote(purrr::pmap_int))
mapping_lgl <- m_lgl <- mapping_impl(quote(purrr::pmap_lgl))
mapping_raw <- m_raw <- mapping_impl(quote(purrr::pmap_raw))

############
# EXAMPLES #
############

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# use appropriate variant instead of map
mapping$sum(!? mtcars[1:3])
#> $mpg
#> [1] 642.9
#> 
#> $cyl
#> [1] 198
#> 
#> $disp
#> [1] 7383.1
mapping_dbl$sum(!? mtcars[1:3])
#>    mpg    cyl   disp 
#>  642.9  198.0 7383.1


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# no need to reposition arguments, just mark them, only marked arguments are vectorized
set.seed(1)
mapping$rnorm(4, !? 1:2) 
#> [[1]]
#> [1] 0.3735462 1.1836433 0.1643714 2.5952808
#> 
#> [[2]]
#> [1] 2.329508 1.179532 2.487429 2.738325


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# this unifies map and pmap and avoids nesting and visual confusion in mutate/transform calls
transform(
  head(iris,2),
  x = mapping_dbl$median(!?Sepal.Width, !?Sepal.Length, !?Petal.Width))
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species   x
#> 1          5.1         3.5          1.4         0.2  setosa 3.5
#> 2          4.9         3.0          1.4         0.2  setosa 3.0
```

<sup>Created on 2019-10-30 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0)</sup>

!~ might be better, as ~ already has the notion of "expanding", while ? means "question"