Category:Lambdatalk

Lambdatalk
This programming language may be used to instruct a computer to perform a task.

See Also:	Lambdatalk on the HOPL

Listed below are all of the tasks on Rosetta Code which have been solved using Lambdatalk.

The {lambda way} project is a web application built on two engines:

1) {lambda tank}, a tiny wiki built as a thin overlay on top of any web browser,

2) {lambda talk}, a purely functional language unifying authoring, styling and scripting in a single and coherent s-expression based syntax.

A) {lambda talk} in few words

1) Expressions are written in a prefix notation using curly braces.

2) Away from curly braces words are just words.

 2+3 is equal to {+ 2 3} 
 -> 2+3 is equal to 5

• 3) Functions are created with lambda and named with def.

 {def foo 
  {lambda {:a :b} 
   :a+:b is equal to {+ :a :b}}} 
 -> foo
 {foo 2 3} 
 -> 2+3 is equal to 5

B) {lambda talk}'s foundations

{lambda talk} is freely inspired by the λ-calculus. At the lowest level a {lambda talk} expression is exclusively made of words, abstractions and applications:

 expression is [word|abstraction|application]*
   where
 1) word        is [^\s{}]*                      -> word
 2) abstraction is {lambda {words} expression}   -> word
 3) application is {expression expression}       -> words

1) a word is any character except spaces and curly braces, and is not evaluated out of curly braces,

2) an abstraction is a special form (called a function) selecting words (called arguments) in an expression (called the body), and is evaluated to a word referencing an anonymous function added to a single dictionary, initially empty,

3) an application is a simple form calling an abstraction to replace selected words by some other words (called values), and is evaluated to words.

The evaluation stops when all expressions have been replaced by words.

Implementation

{lambda talk} is not implemented following the standard process, code -> tokens -> tree -> eval. The code is a string from beginning to end. At each keyboard input, the code is processed by a single function, do_eval(), which returns words sent to the browser for the final evaluation and display.

 var do_eval = function( code ) {
   code = pre_processing( code );
   code = eval_lambdas( code );   // {lambda {args} body}
   code = eval_defs( code );      // {def name body}
   code = eval_forms( code );     // {a {b {c ...}}}
   code = post_processing( code );
   return code
 };

Using a single regular expression the eval_forms() function loops over the code string, skips the words out of curly braces, matches nested forms {first rest} from inside out, and replaces them by words. The repeated substitutions inside the code string overcomes limitations of regular language. It's a kind of Turing machine.

The eval_lambdas() function uses arguments as Regular Expressions to successively replace occurences found in the function's body by the given values. Lambdas have the following properties:

- lambdas are first class functions, they can be called as functions' arguments and returned from functions,

- lambdas are pure black boxes, they don't create closures and are context free, inner lambdas don't see outer functions' arguments, there are no lexical scoping, no free variables,

- lambdas accept de facto partial function application: called with a number of values lesser than its arity, a lambda memorizes the given values and returns a new lambda waiting for the rest.

B) {lambda talk} full

In its complete state, {lambda talk} comes with more special forms, [lambda, def, if, let, quote, macro, require, script, style], and a dictionary containing about 200 primitives built on Javascript Math object, the DOM, HTML tags and CSS rules and more, pairs, lists, arrays, ...

As a dwarf standing on their shoulders, {lambda talk} takes benefit from the extraordinary power of modern web browsers. It does not re-invent the wheel and simply adds a coherent and unique language on existing tools.

The {lambda way} project adds on browsers a thin overlay, {lambda tank}, proposing a small "Interactive Development Environment" without any external dependencies and thereby easy to download and install on any web account provider running PHP.

From any web browser, on any system, complex and dynamic web pages can be created, enriched, structured and tested in real time on the web.

A full presentation of {lambda talk} can be seen in:

 - http://lambdaway.free.fr/
 - http://lambdaway.free.fr/workshop/?view=about
 - http://lambdaway.free.fr/workshop/?view=oxford_slides
 - and several other pages of the workshop.