Clojure-style cond macro in R

cond.R

library(magrittr)

cond <- function(...) {
    # Clojure-style cond macro in R -- creates nested if-else calls
    # arguments: pairs -- condition1, what-if-true1,
    #                     condition2, what-if-true2,
    #                     etc...
    #                                 what-if-all-contitions-false
    e <- parent.frame()
    substitute(list(...)) %>%
        as.list %T>%
        {if (length(.) < 4)
            stop('\ncond requires at least 3 arguments!',
                call.=FALSE)} %>%
        tail(-1) %T>%
        {if (length(.) %% 2 != 1)
            stop('\ncond requires an uneven number of arguments!',
                call.=FALSE)} %>%
        split(((seq_along(.) + 1)/2) %>%
                  floor) %>%
        rev %>%
        {c(.[[1]], tail(., -1))} %>%
        Reduce(function(x,y)
            list(`if`, y[[1]], y[[2]], x) %>%
                as.call, .) %>%
        eval(envir=e)
}

# Example based on the first example from
# https://clojuredocs.org/clojure.core/cond
#
# `pos-neg-or-zero` <- function(n)
#                      cond(n < 0, 'negative',
#                           n > 0, 'positive',
#                                  'zero')
# `pos-neg-or-zero`(5)
# => "positive"
# `pos-neg-or-zero`(-1)
# => "negative"
# `pos-neg-or-zero`(0)
# => "zero"

condv <- function(...) {
    # Clojure-style cond macro in R -- creates nested if-else calls
    # A vectorised version using R's ifelse function rather than if
    # arguments: pairs -- condition1, what-if-true1,
    #                     condition2, what-if-true2,
    #                     etc...
    #                                 what-if-all-contitions-false
    e <- parent.frame()
    substitute(list(...)) %>%
        as.list %T>%
        {if (length(.) < 4)
            stop('\ncondv requires at least 3 arguments!',
                call.=FALSE)} %>%
        tail(-1) %T>%
        {if (length(.) %% 2 != 1)
            stop('\ncondv requires an uneven number of arguments!',
                call.=FALSE)} %>%
        split(((seq_along(.) + 1)/2) %>%
                  floor) %>%
        rev %>%
        {c(.[[1]], tail(., -1))} %>%
        Reduce(function(x,y)
            list(quote(ifelse), y[[1]], y[[2]], x) %>%
                as.call, .) %>%
        eval(envir=e)
}