Scandalbars Mark Wunsch @markwunsch 

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Agenda • What is this whole templating thing all about? • Why even bother? • How did you do this crazy thing? 

The World Wide Web Client Server HTTP 

The World Wide Web Client Server HTTP 

The World Wide Web Client Server HTTP 

The World Wide Web Client Server HTTP HTML 

The World Wide Web Client Server HTTP 

The World Wide Web Client Server HTTP 

The World Wide Web Client Server HTTP JSON 

handlebarsjs.com 

SINGLE-PAGE APPS 

SINGLE-PAGE APPS jsappsfailinghorrifically.tumblr.com 

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Client Server HTTP 

Client Server HTTP 

Client Server HTTP HTML 

Client Server HTTP HTML Accept: application/json 

Client Server HTTP HTML Accept: application/json JSON 

Templating 

${brandName}

${brandName}



} mustache.github.io 

scalate.fusesource.org 

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handlebarsjs.com 

// Template <div class="entry"> <h1>{{title}}</h1> <div class="body"> {{body}} </div> </div> // Code var source = $("#entry-template").html(); var template = Handlebars.compile(source); var context = {title: "My New Post", body: "This is my first post!"} var html = template(context); // Result 

“Maybe I’ll just write Handlebars in Scala,” I finally said to Tom. We were at a bar at the time, and I was a bit tipsy, but there was a “yeah, sure, do that” vibe to our conversation. http://tech.gilt.com/post/59708050425/handlebars-scala-a-handlebars-for-scala 

recursive descent into madness 

http://zaach.github.io/jison/ 

%start root %% root : program EOF { return $1; } ; program : simpleInverse statements { $$ = new yy.ProgramNode([], $2); } | statements simpleInverse statements { $$ = new yy.ProgramNode($1, $3); } | statements simpleInverse { $$ = new yy.ProgramNode($1, []); } | statements { $$ = new yy.ProgramNode($1); } | simpleInverse { $$ = new yy.ProgramNode([], []); } | "" { $$ = new yy.ProgramNode([]); } ; statements : statement { $$ = [$1]; } | statements statement { $1.push($2); $$ = $1; } ; statement : openInverse program closeBlock { $$ = new yy.BlockNode($1, $2.inverse, $2, $3); } | openBlock program closeBlock { $$ = new yy.BlockNode($1, $2, $2.inverse, $3); } | mustache { $$ = $1; } | partial { $$ = $1; } | CONTENT { $$ = new yy.ContentNode($1); } | COMMENT { $$ = new yy.CommentNode($1); } 

λ 

Parser Combinators http://eprints.nottingham.ac.uk/221/1/parsing.pdf 

abstract class Parser[+T] extends (Input) 㱺 ParseResult[T] 

def *: Parser[List[T]] def >>[U]:(fq: (T) => Parser[U]): Parser[U] def ^^[U]:(f: (T) => U): Parser[U] def |[U>: T](q:=> Parser[U]): Parser[U] def ~[U](q:=> Parser[U]): Parser[~[T,U]] Combinators 

def *: Parser[List[T]] def >>[U]:(fq: (T) => Parser[U]): Parser[U] def ^^[U]:(f: (T) => U): Parser[U] def |[U>: T](q:=> Parser[U]): Parser[U] def ~[U](q:=> Parser[U]): Parser[~[T,U]] Combinators 

scala.util.parsing 

def ident: Parser[String] // Anything that is a valid Java identifier, according the The Java Language Spec. def wholeNumber: Parser[String] // An integer, without sign or with a negative sign. def stringLiteral: Parser[String] // Double quotes (") enclosing a sequence of... implicit def regex(r: Regex): Parser[String] implicit def literal(s: String): Parser[String] scala.util.parsing.combinator.JavaTokenParsers 

def statements = rep1(statement) def statement = { inverseBlock | block | mustache | partial | CONTENT ^^ { Content(_) } | comment } 

def statements = rep1(statement) def statement = { inverseBlock | block | mustache | partial | CONTENT ^^ { Content(_) } | comment } statements : statement { $$ = [$1]; } | statements statement { $1.push($2); $$ = $1; } ; statement : openInverse program closeBlock { $$ = new yy.BlockNode($1, $2.inverse, $2, $3); } | openBlock program closeBlock { $$ = new yy.BlockNode($1, $2, $2.inverse, $3); } | mustache { $$ = $1; } | partial { $$ = $1; } | CONTENT { $$ = new yy.ContentNode($1); } | COMMENT { $$ = new yy.CommentNode($1); } ; 

def mustache: Parser[Mustache] = { mustachify(pad(inMustache)) ^^ { mustacheable(_) } | mustachify("&" ~> pad(inMustache)) ^^ { mustacheable(_, true) } | mustachify("{" ~> pad(inMustache) <~ "}") ^^ { mustacheable(_, true) } } 

// Template val template = """

Hello, my name is {{name}}. I am from {{hometown}}. I have {{kids.length}} kids:

{{#kids}}
• {{name}} is {{age}}
{{/kids}}

""" // Object object Guy { val name = "Alan" val hometown = "Somewhere, TX" val kids = Seq(Map( "name" -> "Jimmy", "age -> "12" ), Map( "name" -> "Sally", "age" -> "4" )) } // Result scala> val t = Handlebars(template) t: com.gilt.handlebars.Handlebars = com.gilt.handlebars.Handlebars@496d864e scala> t(Guy) res0: String = "

Hello, my name is Alan. I am from Somewhere, TX. I have 2 kids:

• Jimmy is 12
• Sally is 4

" 

trait Handlebars { def apply[T](context: T): String } 

JSON 

types 

Implicit conversions will not work in a template. Because Handlebars.scala makes heavy use of reflection. Bummer, I know. This leads me too... Handlebars.scala makes heavy use of reflection. This means that there could be unexpected behavior. Method overloading will behave in bizarre ways. There is likely a performance penalty. I'm not sophisticated enough in the arts of the JVM to know the implications of this. 

An Existential Crisis 

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github.com/mwunsch/handlebars.scala 

{{thanks}}