An embeddable LISP interpreter for Swift
The framework converts string literals in nested structures based on the
SExpr enum that can then be evaluated.
Let's see some usage examples:
import SwiftyLisp var expr:SExpr = "(cond ((atom (quote A)) (quote B)) ((quote true) (quote C)))" print(expr) dump(expr) print(expr.eval()!) //B expr = "(car ( cdr ( quote (1 2 \"aaaa\" 4 5 true 6 7 () ))))" print(expr.eval()!) //2 expr = "( (lambda (x y) (atom x)) a b)" print(expr.eval()!) //true expr = "(defun ff (x) (cond ((atom x) x) (true (ff (car x)))))" print(expr.eval()!) expr = "(ff (quote ((a b) c)))" print(expr.eval()!) //a expr = "(eval (quote (atom (quote A)))" print(expr.eval()!) //true expr = "(defun alt (x) (cond ((or (null x) (null (cdr x))) x) (true (cons (car x) (alt (cddr x))))))" print(expr.eval()!) expr = "(alt (quote (A B C D E))" print(expr.eval()!) //(A C E)
Here is a recap of the available operators:
|(print e)||Prints its sub-expression|
|Eval||(eval e)||Eval evaluates its sub-expression|
|Quote||(quote e)||This atom once evaluated returns its sub-expression as is, e.g. (quote A) = A|
|Car||(car l)||Returns the first element of a non-empty sub-list, e.g. (car (quote (A B C))) = A|
|Cdr||(cdr l)||Returns all the elements of the sub-list after the first in a new list, e.g. (cdr (quote (A B C))) = (B C)|
|Cons||(cons e l)||Returns a new list with e as first element and then the content of the sublist e.g. (cons (quote A) (quote (B C))) = (A B C)|
|Equal||(equal e1 e2)||Returns an atom aptly named true if the two symbolic expressions are recursively equal and the empty list () (that serves as both nil and false value) if they are not, e.g. (equal (car (quote (A B))) = (quote A))|
|Atom||(atom e)||Returns true if the symbolic expression is an atom or an empty list if it is a lis, e.g. (atom A) = true|
|Cond||(cond (p1 e1) (p2 e2) ... (pn en))||Returns the first e expression whose p predicate expression is not equal to the empty list. This is basically a conditional atom with a slightly more convoluted syntax than a common if construct. e.g. (cond ((atom (quote A)) (quote B)) ((quote true) (quote C) = B|
|List||(list e1 e2 ... en)||Returns a list of all the given expressions, identical to applying cons recursively to a sequence of expressions.|
|Lambda||( (lambda (v1 ... vn) e) p1 ... pn)||Defines a lambda expression with body e that describes an anonymous function that uses a series of environment variables v. This function will be evaluated using the provided parameters as value for the variables. e.g. ((lambda (X Y) (cons (car x) y) (quote (A B)) (cdr (quote (C D)))) = (A D)|
|Defun||(defun (v1 ... vn) e)||Define a lambda expression and registers it in the current context to be used when we need it. We'll be able to define a function like (defun cadr (X) (car (cdr x))) and use it in another expression like (cadr (quote (A B C D))).|
Additional examples, and the additional functions and acronyms defined in the paper, can be found in the test suite of the framework.
The library can be installed with either CocoaPods, Carthage or the SwiftPM.
To include it in your project using the Swift Package Manager, add a dependency to your
import PackageDescription let package = Package( ... dependencies: [ ... .Package(url: "https://github.com/uraimo/SwiftyLISP.git") ] )
Regardless of how you added the framework to your project, import it with
The MIT License (MIT)
Copyright (c) 2016 Umberto Raimondi
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