pipe-eager {magrittr}

Eager pipe

Description

Whereas ⁠%>%⁠ is lazy and only evaluates the piped expressions when needed, ⁠%!>%⁠ is eager and evaluates the piped input at each step. This produces more intuitive behaviour when functions are called for their side effects, such as displaying a message.

Note that you can also solve this by making your function strict. Call force() on the first argument in your function to force sequential evaluation, even with the lazy ⁠%>%⁠ pipe. See the examples section.

Usage

lhs %!>% rhs

Arguments

lhs

A value or the magrittr placeholder.

rhs

A function call using the magrittr semantics.

Examples

f <- function(x) {
  message("foo")
  x
}
g <- function(x) {
  message("bar")
  x
}
h <- function(x) {
  message("baz")
  invisible(x)
}

# The following lazy pipe sequence is equivalent to `h(g(f()))`.
# Given R's lazy evaluation behaviour,`f()` and `g()` are lazily
# evaluated when `h()` is already running. This causes the messages
# to appear in reverse order:
NULL %>% f() %>% g() %>% h()

# Use the eager pipe to fix this:
NULL %!>% f() %!>% g() %!>% h()

# Or fix this by calling `force()` on the function arguments
f <- function(x) {
  force(x)
  message("foo")
  x
}
g <- function(x) {
  force(x)
  message("bar")
  x
}
h <- function(x) {
  force(x)
  message("baz")
  invisible(x)
}

# With strict functions, the arguments are evaluated sequentially
NULL %>% f() %>% g() %>% h()

# Instead of forcing, you can also check the type of your functions.
# Type-checking also has the effect of making your function lazy.