lazy pipe

[moodymudskipper]

We can reasonably easily implement a lazy pipe, there's just a weird issue with functional sequences :

library(fastpipe)

`%~>%` <- function (lhs, rhs) 
{
  if (globals$master) {
    sc <- sys.call()
    return(eval_slaves(sc, parent.frame()))
  }
  lhs_call <- substitute(lhs)
  rhs_call <- insert_dot(substitute(rhs))

  if (lhs_call == quote(.)) {
    bare_pipe <- attr(sys.function(), "bare_version")
    res <- call(bare_pipe, lhs_call, rhs_call)
    fs_on()
    return(res)
  }

  if (globals$is_fs) {
    bare_pipe <- attr(sys.function(), "bare_version")
    res <- call(bare_pipe, lhs, rhs_call)
    return(res)
  }

  new_env <- new.env()
  eval(bquote(
    delayedAssign(".", .(lhs_call),eval.env = parent.frame(), assign.env = new_env)))
  eval(rhs_call, envir = new_env, enclos = parent.frame())
}

`%~>>%` <- function (lhs, rhs) {
  lhs_call <- substitute(lhs)
  rhs_call <- substitute(rhs)
  new_env <- new.env()
  eval(bquote(
    delayedAssign(".", .(lhs_call),eval.env = parent.frame(), assign.env = new_env)))
  eval(rhs_call, envir = new_env, enclos = parent.frame())
}

class(`%~>%`) <- class(`%~>>%`) <- "fastpipe"
attr(`%~>%`, "bare_version") <- "%~>>%"

environment(`%~>%`) <- as.environment(asNamespace("fastpipe"))
environment(`%~>>%`) <- as.environment(asNamespace("fastpipe"))


stop("!") %>%
  tryCatch(error = function(e) "An error")
#> Error in force(lhs): !

stop("!") %~>%
  tryCatch(error = function(e) "An error")
#> [1] "An error"

stop("!") %~>>%
  tryCatch(error = function(e) "An error")
#> [1] "An error"

"!" %>% stop() %~>%
  tryCatch(error = function(e) "An error") %>%
  toupper()
#> [1] "AN ERROR"

fs <- . %>% stop() %~>% 
  tryCatch(error = function(e) "An error") %>%
  toupper()

# this is weird, maybe just a namespace thing, try in package
fs
#> function (.) 
#> . %>>% stop(.) %>>% toupper(.)

# what if it had worked ?
fs <- function(.)
  . %>>% stop(.) %~>>% 
  tryCatch(error = function(e) "An error") %>>%
  toupper(.)

# then as expected
fs("!")
#> [1] "AN ERROR"

msg <- "old"
delayedAssign("x", stop("hi!"))
substitute(x) # shows only 'x', as it is in the global env.
#> x
msg <- "new!"
x # new!
#> Error in eval(expr, envir, enclos): hi!

^{Created on 2019-11-08 by the reprex package (v0.3.0)}