Whisker is a {{Mustache}} implementation in R confirming to the Mustache specification. Mustache is a logicless templating language, meaning that no programming source code can be used in your templates. This may seem very limited, but Mustache is nonetheless powerful and has the advantage of being able to be used unaltered in many programming languages. It makes it very easy to write a web application in R using Mustache templates which could also be re-used for client-side rendering with "Mustache.js".

Mustache (and therefore whisker) takes a simple, but different, approach to templating compared to most templating engines. Most templating libraries, such as Sweave, knitr and brew, allow the user to mix programming code and text throughout the template. This is powerful, but ties your template directly to a programming language and makes it difficult to seperate programming code from templating code.

Whisker, on the other hand, takes a Mustache template and uses the variables of the current environment (or the supplied list) to fill in the variables.

The syntax of Mustache templates is described in http://mustache.github.com/mustache.5.html How the mustache template are used with whisker can be found in the whisker documentation, and below.

Whisker conforms to the Mustache 1.1 specificaton except for delimiter switching and lambdas. We expect that these will be implented shortly.

To install whisker use the following statement in your R console

install.packages("whisker")

The latest whisker version is not yet available on CRAN, but can be installed from github:

library(devtools)

# dev_mode()
install_github("whisker", "edwindj")

whisker.render accepts a character template and a list or environment containing data to render:

library(whisker)
template <- 
'Hello {{name}}
You have just won ${{value}}!
{{#in_ca}}
Well, ${{taxed_value}}, after taxes.
{{/in_ca}}
'

data <- list( name = "Chris"
            , value = 10000
            , taxed_value = 10000 - (10000 * 0.4)
            , in_ca = TRUE
            )

text <- whisker.render(template, data)
cat(text)

## Hello Chris
## You have just won $10000!
## Well, $6000, after taxes.

Or using a text file

library(whisker)

template <- readLines("./template.html")
data <- list( name = "Chris"
            , value = 10000
            , taxed_value = 10000 - (10000 * 0.4)
            , in_ca = TRUE
            )

writeLines(whisker.render(template, data), "./output.html")

By default whisker applies html escaping on the generated text. To prevent this use {{{variable}}} (triple) in stead of {{variable}}.

template <- 
"I'm escaped: {{name}}
And I'm not: {{{name}}}"

data <- list( name = '<My Name="Nescio">')
whisker.render(template, data)

Generates:

I'm escaped: <My Name="Nescio">
And I'm not: <My Name="Nescio">