typed

gistfile1.txt

options(typed.typed = TRUE)

`%typed%` <- function(e1, e2) {
  if(getOption("typed.typed")) {
    assert_call <- substitute(e1)
    assert_call[[1]] <- quote(assertthat::assert_that)
    eval.parent(assert_call)
  }
  e2
}

types <- function(f) {
  b <- body(f)
  if(is.call(b) && identical(b[[1]], quote(`%typed%`)))
    return(as.list(b[[2]])[-1])
  NULL
}

prefix <- function(str, len) {
  is.character(str)
  is.integer(len)
} %typed% {
  substring(str, 1, len)
}

types(prefix)
#> [[1]]
#> is.character(str)
#> 
#> [[2]]
#> is.integer(len)

prefix(42, 1)
#> Error: str is not a character vector

prefix("test", 1)
#> Error: len is not an integer vector

prefix("test", 1L)
#> [1] "t"

options(typed.typed = FALSE)
prefix(42, 1)
#> [1] "4"