Raddle

A minimalist functional language

What?

Raddle is a functional language for manipulating structured documents (XML, HTML, JSON or... Raddle itself).

This library provides only a parser and compiler. It utilizes L3N, a tiny format for encoding the language as a flat stream, and Frink, the core functionality using a reactive approach.

Raddle is inspired by RQL and XQuery.

Getting started

Run npm install to fetch all dependencies. We need them to compile a string of code, for example:

import { parseString, run } from 'raddle';
import { fromStream } from 'l3n';
import * as n from 'frink';
 
parseString("add(1,2)").pipe(toVNodeStream,$o => run($o,{
    modules:{
        n:n
    }
}));

The parser emits an L3N stream, a flat binary encoding of the program. However, the compiler expects a VNode stream, which wraps the binary data into a more convenient interface. See L3N for more information.

The compiler takes a confuration object with at least the module containing the core functions. The default prefix for this is n, but this may be configured as well in the near future.

Definition Anatomy

The dollar sign provides a context where stuff can be assigned to, and it can be called as a function. So you could write:

$(name[,documentation][,type],body)

Character strings don't have to be written in quotes always. Only in cases where ambiguity with reserved characters would arise, a string should be notated between a pair of (single or double) quotes.

To retrieve the value from the variable, you can call the dollar function with its name:

$(name)

However, you may leave off the parentheses for a shorthand notation:

$name

Lambdas

Functions can be defined in the same way as variables are assigned. Anonymous functions (also known as lambdas) are written within a block of curly brackets. Each parameter of the lambda is referenced numerically, in the order that the function will receive it when it's called, for instance:

{add($1,$2)}

Whenever a new lambda function is created, all previous numbered parameters go out of scope. This way inline functions can also be created. So when a parameter needs to be adressed in a nested lambda, its value should be assigned to a named variable first, since named variables are scoped to the entire block of curly brackets they're in. Example:

{$(x,$1),$(y,$2),add($x,$y)}

Top-level functions

$* declare a module

A module must be explicitly prefixed:

$*(my-module)

$< import a module

$*(other-module,"path")

$> export a constant

$>(my-module:compute,body)

If you don't want to expose the constant, just leave off the > sign.

Types

Types can be provided as function calls:

• string()
• number() (Equivalent to double())
• integer()
• array()
• array(T) (T is the type of the items in the array.)
• map()
• map(K,V) (K is the type of the key and V is the type of the value.)
• function() (A function with an unknown number of arguments. This is the default constraint for any lambda.)
• function(S,R) (S is a sequence of parameter types, and R is the type of the value the function should return.)
• element(Q) (Q is the qualified name of the XML element)
• attribute(Q) (Q is the qualified name of the XML attribute)

Partial application

Any function can be partially applied by using a question mark as a placeholder for an unknown parameter:

add(?,4)

The above function call returns a partially applied function that can be called with a single argument.