seval.js

> S-expression evaluator for TypeScript/JavaScript


seval.js is a safe, sandboxed S-expression parser and evaluator. It's designed to be easily extensible and embeddable in JavaScript/TypeScript applications.

Installation

``bash
npm install seval.js


or


bun add seval.js
`

Quick Start

`typescript
import { evalString, createEvaluator } from 'seval.js'

// Simple evaluation
evalString('(+ 1 2 3)') // 6
evalString('(* 2 (+ 3 4))') // 14

// Conditional and logic
evalString('(if (> 5 3) "yes" "no")') // "yes"
evalString('(and true (not false))') // true

// Lambda and closures
evalString('((lambda (x) (* x x)) 5)') // 25

// Custom primitives
const evaluator = createEvaluator({
primitives: {
uuid: () => crypto.randomUUID(),
greet: (args) => Hello, ${args[0]}!,
}
})
evaluator.evalString('(greet "World")') // "Hello, World!"
`

Features

- Safe sandboxed evaluation - No access to global scope or dangerous APIs
- Rich primitive library - 60+ built-in functions for math, strings, arrays, objects
- Lambda and closures - First-class functions with lexical scoping
- Customizable - Add or override primitives easily
- TypeScript support - Full type definitions included

Built-in Primitives

$3


+, -, *, /, %

$3

=, !=, <, >, <=, >=

$3

and, or, not

$3

abs, min, max, floor, ceil, round, sqrt, pow, clamp, sin, cos, tan, log, exp, random

$3

concat, str, strlen, substr, str-starts-with, str-ends-with, str-contains, str-replace, str-split, str-join, str-trim, str-upper, str-lower, parse-num, parse-int

$3

list, length, first, rest, last, nth, append, prepend, concat-lists, slice, reverse, range, empty?, contains, index-of

$3

obj, get, set, keys, values, has-key, update-at, merge

$3

null?, number?, string?, bool?, list?, object?

Special Forms

`lisp
; Conditionals
(if condition then-expr else-expr)
(cond (test1 expr1) (test2 expr2) (else exprN))

; Variable bindings
(let ((x 1) (y 2)) (+ x y))

; Functions
(lambda (x y) (+ x y))
(define (square x) (* x x))
(define pi 3.14159)

; Sequences
(begin expr1 expr2 ...)
(progn expr1 expr2 ...)

; Higher-order functions
(map (lambda (x) (* x 2)) (list 1 2 3)) ; (2 4 6)
(filter (lambda (x) (> x 2)) (list 1 2 3 4)) ; (3 4)
(reduce (list 1 2 3) 0 (acc x) (+ acc x)) ; 6
`

API

$3

Parse and evaluate an S-expression string.

$3

Evaluate a parsed S-expression AST.

$3

Parse an S-expression string into an AST.

$3

Convert an AST back to string.

$3

Create a custom evaluator with additional primitives.

`typescript
interface EvaluatorOptions {
primitives?: Record
maxDepth?: number // default: 100
}
``

License

MIT