icecream

icecream - never use print() to debug again

This package is an implementation of the icecream package for R. A great part of this document is also adapted.

To install the current version (under active development!) use

devtools::install_github("DominikRafacz/icecream")

But why should I use it?

Do you ever use print() to debug your code? Of course you do. IceCream, or ic for short, makes print debugging a little sweeter.

ic() is like print(), but better:

1. It prints both expressions/variable names and their values.
2. It’s 40% faster to type.
3. Data structures are pretty printed.*
4. Output is syntax highlighted.*
5. It optionally includes program context: filename, line number, and parent function.

Points marked with ’*’ are yet to come. We’ve just begun!

Inspect Variables

Have you ever printed variables or expressions to debug your program? If you’ve ever typed something like

print(foo("123"))

or the more thorough

print('foo("123")', foo("123"))

then ic() is here to help. With arguments, ic() inspects itself and prints both its own arguments and the values of those arguments.

library(icecream)

foo <- function(i) i + 333

ic(foo(123))
## ic| foo(123): [1] 456

Similarly,

d <- list(key = list("one"))
ic(d$key[[1]])
## ic| d$key[[1]]: [1] "one"

klass <- structure(list(attr = "yep"))
ic(klass$attr)
## ic| klass$attr: [1] "yep"

Just give ic() a variable or expression and you’re done. Easy.

Inspect Execution

Have you ever used print() to determine which parts of your program are executed, and in which order they’re executed? For example, if you’ve ever added print statements to debug code like

foo <- function() {
  print(0)
  first()

  if (something) {
    print(1)
    second()
  } else {
    print(2)
    third()
  }
}
    

then ic() helps here, too. Without arguments, ic() inspects itself and prints the calling filename, line number, and parent function.

# example.R
library(icecream)

foo <- function() {
  ic()
  2 + 5

  if (3 < 0) {
    ic()
    7 * 8
  } else {
    ic()
    9^0
  }
}

foo()
## ic| example.R:4:2 in global::foo 
## ic| example.R:11:4 in global::foo

Just call ic() and you’re done. Simple.

Return Value

ic() returns its argument(s), so ic() can easily be inserted into pre-existing code.

a <- 6
half <- function(i) i / 2
b <- half(ic(a))
## ic| a: [1] 6
ic(b)
## ic| b: [1] 3