# is.R

##### Are we using R, rather than S?

Test if running under R.

- Keywords
- utilities, environment

##### Usage

`is.R()`

##### Details

The function has been written such as to correctly run in all versions
of R, S and S-PLUS.
In order for code to be runnable in both R and S dialects previous to
S-PLUS 8.0, your code must either define `is.R`

or use it as

`if (exists("is.R") && is.function(is.R) && is.R()) {`

` `

*## R-specific code*
`} else {`

` `

*## S-version of code*
`}`

##### Value

`is.R`

returns `TRUE`

if we are using R and `FALSE`

otherwise.

##### See Also

##### Examples

`library(base)`

```
# NOT RUN {
x <- stats::runif(20); small <- x < 0.4
## In the early years of R, 'which()' only existed in R:
if(is.R()) which(small) else seq(along = small)[small]
# }
```

*Documentation reproduced from package base, version 3.5.0, License: Part of R 3.5.0*

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