R-Expressions

R-expressions or Rich Expressions is a language inspired by S- and M-expressions. The toolkit is written with JavaScript and contains:

✅ Tokenizer,
✅ Parser,
✅ Traverser,
✅ Transformer.

Tokenizer and parser support streaming mode with byte-per-byte input and could be used for REPL creation.

Application

R-expressions could be used for:

Lisp-like programming languages creation.
Language prototyping.
Transpilation.

Example

(pseudo-lang ^1.0)

import({Console} from Core.Io)

Console.log('Hello, %s!' 'World')

Types

R-Expressions contains symbols, strings, lists, calls and comments.

Symbol

Symbol is a sequence of characters without whitespaces, single quotes or parenthesis. While whitespace, semicolon, quote or open parenthesis could be escaped by backslash.

These are all symbols:

true
1_000_000
^1.*
Console.log
http://github.com/rumkin/r-expressions
~/memories/summer\ vacation\ 2019/
<node>

String

String is a sequence of characters surrounded by single quote '. Single quote within a string should be escaped with a backslash \. And backslash could be escaped by another backslash \\. String could contain new lines.

'This is a string'
'Hello! I\'m a string too.'
'This is a multiline
string'

Lists

List is a type which can contain other types: symbols, strings, lists, and calls:

R-expressions has three types of lists round, square, and figure, this lists are enclosed with round, square, or figure parenthesis respectively. They can be used to separate semantic.

; Round parenthesis list
(null true 1_234 'Hello')

; Figure parenthesis list
{x: 1 y: 2 z: 3}

; Square parenthesis list
[1 2 3 4 5]

; Mixed
[a (1 {2} 3) b]

; Empty
()

⚠️ There should be a space between the closing parenthesis of a list and the opening of a following one. While this code {} {} is correct, the next one {}{} is not. Look at Call type.

Call

Call is a type which specifies function call and is presented by symbol followed by a list:

print('Hello world')

Calls could be chained, if there is no space between lists in a sequence:

curry(print 'Hello, %s')('World')
; or
print('Hello, %s' ?)('World')

Lists types could be mixed for different semantics creation:

; HTML like code
div{class: !['badge' 'badge-round' 'badge-red']}(
  p('Users count: 1')
)

Comment

Comment is a line of text prepended with a semicolon ;. Comment ends with new line char \n.

; Hi! I'm a comment. I can help you to describe your program

rumkin/r-expr