Tools for defensive programming, inspired by {purrr}
mappers and based
on {rlang}
.
{attempt}
is designed to handle the cases when something / someone
attempts to do something it shouldn’t.
For example:
log("a")
(error)paste()
"good morning"
and iris
(message/warning){attempt}
provides several condition handlers, from try catch to
simple message printing.
{attempt}
only depends on {rlang}
, and every function is design to
be fast, making it easy to implement in other functions and packages.
From CRAN:
install.packages("attempt")
The dev version:
install.packages("attempt", repo = "https://colinfay.me/ran")
library(attempt)
attempt()
is a wrapper around base try()
that allows you to insert a
custom messsage on error.
attempt(log("a"))
# Error: non-numeric argument to mathematical function
attempt(log("a"), msg = "Nop !")
# Error: Nop !
You can make it verbose (i.e. returning the expression):
attempt(log("a"), msg = "Nop !", verbose = TRUE)
# Error in log("a"): Nop !
Of course the result is returned if there is one:
attempt(log(1), msg = "Nop !", verbose = TRUE)
# [1] 0
As with try()
, the result can be saved as an error object:
a <- attempt(log("a"), msg = "Nop !", verbose = TRUE)
a
# [1] "Error in log(\"a\"): Nop !\n"
# attr(,"class")
# [1] "try-error"
# attr(,"condition")
# <simpleError in log("a"): Nop !>
You can check if the result is an error with is_try_error()
a <- attempt(log("a"), msg = "Nop !", verbose = FALSE)
#> Error: Nop !
is_try_error(a)
#> [1] TRUE
silent_attempt()
is a wrapper around silently()
(see further down
for more info) and attempt()
. It attempts to run the expr, stays
silent if the expression succeeds, and returns error or warnings if any.
silent_attempt(log("a"))
# Error: non-numeric argument to mathematical function
silent_attempt(log(1))
You can write a try catch with these params:
expr
the expression to be evaluated.e
a mapper or a function evaluated when an error occurs.w
a mapper or a function evaluated when a warning occurs.f
a mapper or an expression which is always evaluated before
returning or exitingIn .e
and .f
, the .x
refers to the error / warning object.
try_catch(expr = log("a"),
.e = ~ paste0("There is an error: ", .x),
.w = ~ paste0("This is a warning: ", .x))
#[1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"
try_catch(log("a"),
.e = ~ stop(.x),
.w = ~ warning(.x))
# Error in log("a") : non-numeric argument to mathematical function
try_catch(matrix(1:3, nrow= 2),
.e = ~ print(.x),
.w = ~ print(.x))
#<simpleWarning in matrix(1:3, nrow = 2): data length [3] is not a sub-multiple or multiple of the number of rows [2]>
try_catch(expr = 2 + 2 ,
.f = ~ print("Using R for addition... ok I'm out!"))
# [1] "Using R for addition... ok I'm out!"
# [1] 4
As usual, the handlers are set only if you call them:
try_catch(matrix(1:3, nrow = 2), .e = ~ print("error"))
# [,1] [,2]
# [1,] 1 3
# [2,] 2 1
# Warning message:
# In matrix(1:3, nrow = 2) :
# data length [3] is not a sub-multiple or multiple of the number of rows [2]
try_catch(matrix(1:3, nrow = 2), .w = ~ print("warning"))
# [1] "warning"
{attempt}
is flexible in how you can specify your arguments.
You can, as you do with {base}
tryCatch()
, use a plain old function:
try_catch(log("a"),
.e = function(e){
print(paste0("There is an error: ", e))
print("Ok, let's save this")
time <- Sys.time()
a <- paste("+ At",time, ", \nError:",e)
# write(a, "log.txt", append = TRUE) # commented to prevent log.txt creation
print(paste("log saved on log.txt at", time))
print("let's move on now")
})
# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"
# [1] "Ok, let's save this"
# [1] "log saved on log.txt at 2018-01-30 16:59:13"
# [1] "let's move on now"
You can even mix both:
try_catch(log("a"),
.e = function(e){
paste0("There is an error: ", e)
},
.f = ~ print("I'm not sure you can do that pal !"))
# [1] "I'm not sure you can do that pal !"
# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"
try_catch(log("a"),
.e = ~ paste0("There is an error: ", .x),
.f = function() print("I'm not sure you can do that pal !"))
# [1] "I'm not sure you can do that pal !"
# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"
try_catch_df()
try_catch_df()
returns a tibble with the call, the error message if
any, the warning message if any, and the value of the evaluated
expression or “error”. The values will always be contained in a
list-column.
res_log <- try_catch_df(log("a"))
res_log
#> call error warning value
#> 1 log("a") non-numeric argument to mathematical function NA error
res_log$value
#> [[1]]
#> [1] "error"
res_matrix <- try_catch_df(matrix(1:3, nrow = 2))
res_matrix
#> call error
#> 1 matrix(1:3, nrow = 2) NA
#> warning
#> 1 data length [3] is not a sub-multiple or multiple of the number of rows [2]
#> value
#> 1 1, 2, 3, 1
res_matrix$value
#> [[1]]
#> [,1] [,2]
#> [1,] 1 3
#> [2,] 2 1
res_success <- try_catch_df(log(1))
res_success
#> call error warning value
#> 1 log(1) NA NA 0
res_success$value
#> [[1]]
#> [1] 0
map_try_catch()
map_try_catch()
and map_try_catch_df()
allow you to map on a list of
arguments l
, to be evaluated by the function in fun
.
map_try_catch(l = list(1, 3, "a"), fun = log, .e = ~ .x)
#> [[1]]
#> [1] 0
#>
#> [[2]]
#> [1] 1.098612
#>
#> [[3]]
#> <simpleError in .Primitive("log")("a"): non-numeric argument to mathematical function>
map_try_catch_df(list(1,3,"a"), log)
#> call error
#> 1 .Primitive("log")(1) <NA>
#> 2 .Primitive("log")(3) <NA>
#> 3 .Primitive("log")("a") non-numeric argument to mathematical function
#> warning value
#> 1 NA 0
#> 2 NA 1.098612
#> 3 NA error
Adverbs take a function and return a modified function.
silently()
silently()
transforms a function so that when you call this new
function, it returns nothing unless there is an error or a warning
(contrary to attempt
that returns the result). In a sense, the new
function stay silent unless error or warning.
silent_log <- silently(log)
silent_log(1)
silent_log("a")
#> Error in .f(...) : non-numeric argument to mathematical function
# Error in .f(...) : non-numeric argument to mathematical function
With silently()
, the result is never returned.
silent_matrix <- silently(matrix)
silent_matrix(1:3, 2)
#Warning message:
#In .f(...) :
# data length [3] is not a sub-multiple or multiple of the number of rows [2]
surely()
surely()
transforms a function so that when you call this new
function, it calls attempt()
- i.e. in the code below, calling
sure_log(1)
is the same as calling attempt(log(1))
. In a sense,
you’re sure this new function will always work.
sure_log <- surely(log)
sure_log(1)
# [1] 0
sure_log("a")
# Error: non-numeric argument to mathematical function
with_message()
and with_warning()
These two functions take a function, and add a warning or a message to it.
as_num_msg <- with_message(as.numeric, msg = "We're performing a numeric conversion")
as_num_warn <- with_warning(as.numeric, msg = "We're performing a numeric conversion")
as_num_msg("1")
#> We're performing a numeric conversion
#> [1] 1
as_num_warn("1")
#> Warning in as_num_warn("1"): We're performing a numeric conversion
#> [1] 1
without_message()
, without_warning()
, and discretly()
These three functions do the opposite, as they remove warnings and messages:
matrix(1:3, ncol = 2)
no_warning_matrix <- without_warning(matrix)
no_warning_matrix(1:3, ncol = 2)
if_
conditionsif_none()
, if_any()
and if_all()
test the elements of the list.
if_all(1:10, ~ .x < 11, ~ return(letters[1:10]))
#> [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
if_any(1:10, is.numeric, ~ "Yay!")
#> [1] "Yay!"
if_none(1:10, is.character, ~ rnorm(10))
#> [1] -0.62041260 1.18903502 0.34425236 0.40211829 -0.89651209
#> [6] 0.08673175 -0.65066136 0.47734033 -1.34301785 -0.20193553
The defaut for all .p
is isTRUE()
. So you can:
a <- c(FALSE, TRUE, TRUE, TRUE)
if_any(a, .f = ~ "nop!")
#> [1] "nop!"
if_then()
performs a simple “if this then do that”:
if_then(1, is.numeric, ~ "nop!")
#> [1] "nop!"
if_not()
runs .f
if .p(.x)
is not TRUE :
if_not(.x = 1, .p = is.character, ~ ".x is not a character")
#> [1] ".x is not a character"
And if_else()
is a wrapper around base::ifelse()
.
If you want these function to return a value, you need to wrap these
values into a mapper / a function. E.g, to return a vector, you’ll need
to write if_then(1, is.numeric, ~ "Yay")
.
a <- if_else(1, is.numeric, ~ "Yay", ~ "Nay")
a
#> [1] "Yay"
The stop_if()
, warn_if()
and message_if()
are easy to use
functions that send an error, a warning or a message if a condition is
met. Each function has its counterpart with _not
that returns a
message if the condition is not met.
stop_if_not()
is quite the same as assert_that()
from the
{assertthat} package, except that it can takes mappers. It is not the
same as base stopifnot()
, as it doesn’t take a list of expression.
These functions are also flexible as you can pass base predicates (is.numeric, is.character…), a custom predicate built with mappers, or even your own predicate function.
You can either choose a custom message or just let the built-in messages be printed:
x <- 12
# Stop if .x is numeric
stop_if(.x = x,
.p = is.numeric)
#> Error: Test `is.numeric` on `x` returned an error.
y <- "20"
# stop if .x is not numeric
stop_if_not(.x = y,
.p = is.numeric,
msg = "y should be numeric")
#> Error: y should be numeric
a <- "this is not numeric"
# Warn if .x is charcter
warn_if(.x = a,
.p = is.character)
#> Warning: Test `is.character` on `a` returned a warning.
b <- 20
# Warn if .x is not equal to 10
warn_if_not(.x = b,
.p = ~ .x == 10 ,
msg = "b should be 10")
#> Warning: b should be 10
c <- "a"
# Message if c is a character
message_if(.x = c,
.p = is.character,
msg = "You entered a character element")
#> You entered a character element
# Build more complex predicates
d <- 100
message_if(.x = d,
.p = ~ sqrt(.x) < 42,
msg = "The square root of your element must be more than 42")
#> The square root of your element must be more than 42
# Or, if you're kind of old school, you can still pass classic functions
e <- 30
message_if(.x = e,
.p = function(vec){
return(sqrt(vec) < 42)
},
msg = "The square root of your element must be more than 42")
#> The square root of your element must be more than 42
If you need to call a function that takes no argument at .p
(like
curl::has_internet()
), use this function as
.x
.
stop_if(.x = curl::has_internet(), msg = "You shouldn't have internet to do that")
#> Error: You shouldn't have internet to do that
warn_if(.x = curl::has_internet(),
msg = "You shouldn't have internet to do that")
#> Warning: You shouldn't have internet to do that
message_if(.x = curl::has_internet(),
msg = "Huray, you have internet \\o/")
#> Huray, you have internet \o/
If you don’t specify a .p
, the default test is isTRUE()
.
a <- is.na(airquality$Ozone)
message_if_any(a, msg = "NA found")
#> NA found
That can come really handy inside a function:
my_fun <- function(x){
stop_if_not(.x = curl::has_internet(),
msg = "You should have internet to do that")
warn_if_not(x,
is.character,
msg = "x is not a character vector. The output may not be what you're expecting.")
paste(x, "is the value.")
}
my_fun(head(iris))
#> Warning: x is not a character vector. The output may not be what you're
#> expecting.
#> [1] "c(5.1, 4.9, 4.7, 4.6, 5, 5.4) is the value."
#> [2] "c(3.5, 3, 3.2, 3.1, 3.6, 3.9) is the value."
#> [3] "c(1.4, 1.4, 1.3, 1.5, 1.4, 1.7) is the value."
#> [4] "c(0.2, 0.2, 0.2, 0.2, 0.2, 0.4) is the value."
#> [5] "c(1, 1, 1, 1, 1, 1) is the value."
stop_if()
, warn_if()
and message_if()
all have complementary tests
with _all
, _any
and _none
, which combine the if_*
and the
warn_*
, stop_*
and message_*
seen before. They take a list as
first argument, and a predicate. They test if any, all or none of the
elements validate the
predicate.
stop_if_any(iris, is.factor, msg = "Factors here. This might be due to stringsAsFactors.")
#> Error: Factors here. This might be due to stringsAsFactors.
warn_if_none(1:10, ~ .x < 0, msg = "You need to have at least one number under zero.")
#> Warning: You need to have at least one number under zero.
message_if_all(1:100, is.numeric, msg = "That makes a lot of numbers.")
#> That makes a lot of numbers.
on_error()
on_error()
behaves as on.exit()
except it happens only when there is
an error in the function.
y <- function(x){
on_error(~ print("ouch"))
log(x)
}
y(12)
[1] 2.484907
y("a")
Error in log(x) : non-numeric argument to mathematical function
[1] "ouch"
Thanks to Romain for the name suggestion.
Questions and feedbacks welcome!
You want to contribute ? Open a PR :) If you encounter a bug or want to suggest an enhancement, please open an issue.
Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.
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