Wisp is a homoiconic JavaScript dialect with clojure syntax, s-expressions and macros. Unlike clojurescript, Wisp code compiles to human-readable JavaScript. The goal of Wisp is to compile to the JavaScript you would have written anyway. Think of Wisp as markdown for JS programing!

Homoiconic syntax and macros are the primary motivations!

You can try it before you buy it: http://jeditoolkit.com/wisp/

npm install -g wisp

Wisp is homoiconic JS dialect with a clojure syntax, s-expressions and macros. Wisp code compiles to a human readable javascript, which is one of they key differences from clojurescript.

nil is just like JS undefined with a difference that it cannot be redefined. It's just a shortcut for void(0) in JS.

nil ;; => void(0)

Wisp booleans true / false are plain JS booleans.

true ;; => true

Wisp numbers are JS numbers

1  ;; => 1

Wisp strings are JS Strings

"Hello world"

Wisp strings can be multiline

"Hello,
My name is wisp!"

Characters are syntatic sugar for JS single char strings

\a  ;; => "a"
\b  ;; => "b"

Keywords are symbolic identifiers that evaluate to themselves.

:keyword  ;; => "keyword"

Since in JS string constants fulfill the purpose of symbolic identifiers, keywords compile to equivalent JS strings.

(window.addEventListener :load handler false)

Keywords can also be invoked as functions, that desugars to associated value access in JS:

(:bar foo) ;; => foo["bar"]

Wisp vectors are JS arrays.

[ 1 2 3 4 ]

Note: Commas are whitespace & can be used if desired

[ 1, 2, 3, 4]

Maps are hash maps, plain JS objects. Note that unlike in clojure, keys cannot be of arbitary types.

{ "foo" bar :beep-bop "bop" 1 2 }

Commas are optional but can come handy for separating key value pairs.

{ a 1, b 2 }

In a future JSONs syntax may be made compatible with map syntax.

You can't have a lisp without lists! Wisp is homoiconic and its code is made up of lists representing expressions. The first item in the expression is a function, being invoked with rest items as arguments.

(foo bar baz) ; => foo(bar, baz);

Wisp puts a lot of effort in making naming conventions transparent, by encouraging lisp conventions and then translating them to their equivalent JS conventions:

(dash-delimited)   ;; => dashDelimited
(predicate?)       ;; => isPredicate
(**privates**)     ;; => __privates__
(list->vector)     ;; => listToVector

As a side effect some names can be expressed in a few ways, although it's considered to be an advantage.

(parse-int x)
(parseInt x)

(array? x)
(isArray x)

There are some functions in wisp that are special, in the sense that they compile to JS expressions & cannot be passed around as regular functions. JS operators are represented in wisp as special forms

Wisp comes with special form for arithmetic operations.

(+ a b)        ; => a + b
(+ a b c)      ; => a + b + c
(- a b)        ; => a - b
(* a b c)      ; => a * b * c
(/ a b)        ; => a / b
(mod a b)      ; => a % 2

Wisp comes with special forms for comparisons

(identical? a b)     ;; => a === b
(identical? a b c)   ;; => a === b && b === c
(= a b)              ;; => a == b
(= a b c)            ;; => a == b && b == c
(> a b)              ;; => a > b
(>= a b)             ;; => a >= b
(< a b c)            ;; => a < b && b < c
(<= a b c)           ;; => a <= b && b <= c

Wisp comes with special forms for logical operations

(and a b)            ;; => a && b
(and a b c)          ;; => a && b && c
(or a b)             ;; => a || b
(and (or a b)
     (and c d))      ;; (a || b) && (c && d)

Variable definitions also happen through special forms.

(def a)     ; => var a = void(0);
(def b 2)   ; => var b = 2;

In wisp new values can be set to a variables via set! special form. Note that in functional programing binding changes are a bad practice, avoiding those would make your programs only better! Still if you need it you have it.

(set! a 1)

Conditional code branching in wisp is expressed via if special form. First expression following if is a condition, if it evaluates to true result of the if expression is the second expression, otherwise it's the third expression.

(if (< number 10)
  "Digit"
  "Number")

Else expression is optional, if missing and conditional evaluates to true result will be nil.

(if (monday? today) "How was your weekend")

In wisp is everything is an expression, but sometimes one might want to combine multiple expressions into one, usually for the purpose of evaluating expressions that have side-effects

(do
  (console.log "Computing sum of a & b")
  (+ a b))

do can take any number of expressions, even 0. If 0, the result of evaluation will be nil.

(do) ;; => nil

Let special form evaluates containing expressions in a lexical context of in which symbols in the bindings-forms (first item) are bound to their respective expression results.

(let [a 1
      b (+ a c)]
  (+ a b))

Wisp functions are JS functions

(fn [x] (+ x 1))

Wisp functions can have names, just as in JS

(fn increment [x] (+ x 1))

Wisp functions can also contain documentation and some metadata. Note: Docstrings and metadata are not presented in compiled JS yet, but in the future they will compile to comments associated with function.

(fn incerement
  "Returns a number one greater than given."
  {:added "1.0"}
  [x] (+ x 1))

Wisp makes capturing of rest arguments a lot easier than JS. argument that follows special & symbol will capture all the rest args in array.

(fn [x & rest]
  (rest.reduce (fn [sum x] (+ sum x)) x))

In wisp functions can be overloaded depending on number of arguments they take, without introspection of rest arguments.

(fn sum
  "Return the sum of all arguments"
  {:version "1.0"}
  ([] 0)
  ([x] x)
  ([x y] (+ x y))
  ([x & more] (more.reduce (fn [x y] (+ x y)) x)))

If function does not has variadic overload and more arguments is passed to it, it throws exception.

(fn
  ([x] x)
  ([x y] (- x y)))

In wisp type instantiation has a concise form. The type function just needs to be suffixed with . character

(Type. options)

The more verbose but more JS-like form is also valid

(new Class options)

In wisp method calls are no different from function calls, it's just that method functions are prefixed with . character

(.log console "hello wisp")

More JS-like forms are supported too!

(window.addEventListener "load" handler false)

In wisp attribute access is also just like function call. Attribute name just needs to be prefixed with .-

(.-location window)

Compound properties can be access via get special form

(get templates (.-id element))

In wisp exceptions can be handled via try special form. As with everything else, the try form is also expression. It results to nil if no handling takes place.

(try (raise exception))

Although the catch form can be used to handle exceptions

(try
  (raise exception)
  (catch error (.log console error)))

Also finally clause can be used when necessary

(try
  (raise exception)
  (catch error (recover error))
  (finally (.log console "That was a close one!")))

Throw special form allows throwing exceptions, although doing that is not idiomatic.

(fn raise [message] (throw (Error. message)))

Wisp has a programmatic macro system which allows the compiler to be extended by user code. Many core constructs of Wisp are in fact normal macros.

Before diving into macros too much, we need to learn about few more things. In lisp any expression can be marked to prevent it from being evaluated. For instance, if you enter the symbol foo you will be evaluating the reference to the value of the corresponding variable.

foo

If you wish to refer to the literal symbol, rather than reference you could use

(quote foo)

or more usually

'foo

Any expression can be quoted, to prevent its evaluation. Although your resulting programs should not have these forms compiled to JS.

'foo
':bar
'(a b)

Wisp doesn’t have unless special form or a macro, but it's trivial to implement it via macro. Although let's try implemting it as a function to understand a use case for macro!

We want to execute body unless condition is true.

(defn unless-fn [condition body]
  (if condition nil body))

Although following code will log "should not print" anyway, since function arguments are exectued before function is called.

(unless-fn true (console.log "should not print"))

Macros solve this problem, because they do not evaluate their arguments immediately. Instead, you get to choose when (and if!) the arguments to a macro are evaluated. Macros take items of the expression as arguments and return new form that is compiled instead.

(defmacro unless
  [condition form]
  (list 'if condition nil form))

The body of unless macro executes at macro expansion time, producing an if form for compilation. Later this is compiled as usual. This way the compiled JS is a conditional instead of function call.

(unless true (console.log "should not print"))

Simple macros like above could be written via templating, expressed as syntax-quoted forms.

syntax-quote is almost the same as the plain quote, but it allows sub expressions to be unquoted so that form acts a template. Symbols inside form are resolved to help prevent inadvertent symbol capture. Which can be done via unquote and unquote-splicing forms.

(syntax-quote (foo (unquote bar)))
(syntax-quote (foo (unquote bar) (unquote-splicing bazs)))

Note that there is special syntactic sugar for both unquoting operators:

Syntax quote: Quote the form, but allow internal unquoting so that the form acts as template. Symbols inside form are resolved to help prevent inadvertent symbol capture.

`(foo bar)

Unquote: Use inside a syntax-quote to substitute an unquoted value.

`(foo ~bar)

Splicing unquote: Use inside a syntax-quote to splice an unquoted list into a template.

`(foo ~bar ~@bazs)

For example, the built-in defn macro can be defined expressed with simple template macro. That's more or less how build-in defn macro is implemented.

(defmacro define-fn
  [name & body]
  `(def ~name (fn ~@body)))

Now if we use define-fn form above defined macro will be expanded and compile time resulting into diff program output.

(define-fn print
  [message]
  (.log console message))

Not all of the macros can be expressed via templating, but all of the language is available at hand to assemble macro expanded form. For instance let's define a macro to ease functional chaining popular in JS but usually expressed via method chaining. For example following API is pioneered by jQuery is very common in JS:

open(target, "keypress").
  filter(isEnterKey).
  map(getInputText).
  reduce(render)

Unfortunately though it usually requires all the functions need to be methods of dsl object, which is very limited. Making third party functions second class. Via macros we can achieve similar chaining without such tradeoffs.

(defmacro ->
  [& operations]
  (reduce-list
   (rest operations)
   (fn [form operation]
     (cons (first operation)
           (cons form (rest operation))))
   (first operations)))


(->
 (open target :keypress)
 (filter enter-key?)
 (map get-input-text)
 (reduce render))