tests/testthat/examples/knitr-examples/106-polyglot.md

In parsermd: Formal Parser and Related Tools for R Markdown Documents

A Knitr "Polyglot" Example for Markdown

This is a minimal example of using "polyglot"" knitr to produce an HTML page from Markdown.

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

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.

Sys.setenv(SOMETHING = "something")

Compute Something in R

something <- Sys.getenv("SOMETHING")
somethingelse <- paste(something, "+ R")
cat(paste("'", something, "' is now '", somethingelse, "'", sep = ""))

R> 'something' is now 'something + R'

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.

val something = System.getenv("SOMETHING")
val somethingelse = something + " + Scala"
println("'" + something + "' is now '" + somethingelse + "'")

Scala> 'something' is now 'something + Scala'

Compute Something in Python

import os
something = os.getenv("SOMETHING")
somethingelse = something + " + Python"
print("'" + something + "' is now '" + somethingelse + "'")

Python> 'something' is now 'something + Python'

Compute Something in Bash

something=$SOMETHING
somethingelse="$something + Bash"
echo "'$something' is now '$somethingelse'"

Bash> 'something' is now 'something + Bash'

Compute Something in Perl

my $something = $ENV{SOMETHING};
$something .= ' + Perl';
say join ' ', qw{something is now}, "'$something'";

Perl> something is now 'something + Perl'

parsermd documentation built on Aug. 21, 2025, 5:27 p.m.