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README.Rmd
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```{r, setup, echo = FALSE, message = FALSE}
knitr::opts_chunk$set(
comment = "#>",
tidy = FALSE,
error = FALSE,
fig.width = 8,
fig.height = 8)
```
# tamper
> Easier Debugging of `magrittr` Pipes
[](https://travis-ci.org/gaborcsardi/tamper)
[](https://ci.appveyor.com/project/gaborcsardi/tamper)
[](http://www.r-pkg.org/pkg/tamper)
[](http://www.r-pkg.org/pkg/tamper)
One difficulty of
[`magrittr`](https://github.com/smbache/magrittr) pipes is that they make
debugging harder. If you don't always write correct code, and you use
pipes, then you'll find `tamper` very useful. It is the `magrittr` specific
alternative of the `recover` function: when used with
`options(error = tamper)`, after an error it displays the whole pipeline,
marks the place of the error, and helps saving the temporary results.
## Installation
```{r eval = FALSE}
devtools::install_github("gaborcsardi/tamper")
```
## Rationale
Pipes make code more readable, but their internal non-standard evaluation sorcery interacts poorly with some development tools, in particular `recover`, which helps inspecting the call stack after an error has occurred.
```r
library(magrittr)
options(error = recover)
1:10 %>%
multiply_by(10) %>%
add(10) %>%
add("oh no!") %>%
subtract(5) %>%
divide_by(5)
Error in add(., "oh no!") : non-numeric argument to binary operator
Enter a frame number, or 0 to exit
1: 1:10 %>% multiply_by(10) %>% add(10) %>% add("oh no!") %>% subtract(5) %>% divide_by(5)
2: withVisible(eval(quote(`_fseq`(`_lhs`)), env, env))
3: eval(quote(`_fseq`(`_lhs`)), env, env)
4: eval(expr, envir, enclos)
5: `_fseq`(`_lhs`)
6: freduce(value, `_function_list`)
7: function_list[[i]](value)
```
Doh? What does that mean? Only @smbache knows! What are mere mortals to do? `tamper` to the rescue.
## Usage
```r
options(error = tamper::tamper)
```
Then, if you make a mistake in a pipeline, instead of the above meta-mumbo-jumbo produced by a clueless `recover`,
`tamper` is invoked and you can explore the data in the pipeline, and also save to a temporary variable.
```r
library(magrittr)
1:10 %>%
multiply_by(10) %>%
add(10) %>%
add("oh no!") %>%
subtract(5) %>%
divide_by(5)
```
You will see:
```r
Error in add(., "oh no!") : non-numeric argument to binary operator
Enter 0 to exit or choose:
1: Switch mode
2: Take me to the error
3: 1:10 %>%
4: multiply_by(., 10) %>%
5: add(., 10) %>%
6: -> add(., "oh no!") %>%
7: subtract(., 5) %>%
8: divide_by(., 5)
Selection:
```
The stage with the error is clearly marked with an arrow. You can get to
the function in which the error happened by selecting `2`. (Unless it
is a primitive function, those are not in the call stack.)
If you select `6`, you can browse the frame that corresponds to the
pipeline stage in which the error happened:
```r
Selection: 6
Called from: eval(substitute(expr), envir, enclos)
Browse[1]> ls()
[1] "function_list" "k" "value"
```
`value` is the value of the `.` dot variable, at the beginning
of the pipeline stage:
```r
Browse[1]> value
[1] 20 30 40 50 60 70 80 90 100 110
```
If you don't want to redo the initial part of the pipeline, you
can save `value` to a global variable in your workspace:
```r
Browse[1]> assign("value", value, envir = globalenv())
```
## Feedback
Please see our
[issue tracker](https://github.com/gaborcsardi/tamper/issues).
## License
MIT © [Gábor Csárdi](https://github.com/gaborcsardi).