# A Knitr "Polyglot" Example for Markdown

This is a minimal example of using "polyglot"" **knitr** to produce an _HTML_ page from _Markdown_.

```{r setup}
knitr::opts_chunk$set(engine.opts = list(
  perl = "-Mstrict -Mwarnings -Mfeature=say",
  bash = "-o errexit -o nounset"
))
toTest <- c("R", "python", "scala", "bash", "perl")
where <- Sys.which(toTest)
```

## Engine runtime paths

```{r list-engines, message=FALSE}
for(n in names(where)) {
  path <- where[n]
  if(nchar(path) <= 0) {
    path <- "<not found>"
  }
  message("* __", n, "__: `", path, "`\n")
}
```

## Input Data

Pass the string to transform to engine subprocess via environment variable.

```{r, echo=TRUE}
Sys.setenv(SOMETHING = "something")
```

## Compute Something in R

```{r something-in-R, engine='R', comment='R>'}
something <- Sys.getenv("SOMETHING")
somethingelse <- paste(something, "+ R")
cat(paste("'", something, "' is now '", somethingelse, "'", sep=""))
```

## Compute Something in Scala

Running small fragments without caching can take some time, as the Scala compiler has to launch and compile the script to JVM bytecode. The `-savecompiled` option (passed via `engine.opts`) will result in Scala caching the compiled script outside of _knitr_.

```{r something-in-Scala, engine='scala', comment='Scala>', engine.opts='-savecompiled -nc', cache=TRUE}
val something = System.getenv("SOMETHING")
val somethingelse = something + " + Scala"
println("'" + something + "' is now '" + somethingelse + "'")
```

## Compute Something in Python

```{r something-in-Python, engine='python', comment='Python>'}
import os
something = os.getenv("SOMETHING")
somethingelse = something + " + Python"
print("'" + something + "' is now '" + somethingelse + "'")
```

## Compute Something in Bash

```{r something-in-Bash, engine='bash', comment='Bash>'}
something=$SOMETHING
somethingelse="$something + Bash"
echo "'$something' is now '$somethingelse'"
```

## Compute Something in Perl

```{r something-in-Perl, engine='perl', comment='Perl>'}
my $something = $ENV{SOMETHING};
$something .= ' + Perl';
say join ' ', qw{something is now}, "'$something'";
```