Scheme Interpreter in Swift

This interpreter was developed for the lecture "Design und Implementation fortgeschrittener Programmiersprachen" at HdM Stuttgart in SS2021. The lecture was given by Claus Gittinger.

The interpreter was built in Swift 5.4.2 as an executable Swift package. For full functionality, swift-tools-version:5.3 is required. As an alternative, the interpreter was also created as a command line project for Xcode 10.1, which can be found at: Xcode 10.1 project

Build

The build process can either be executed automatically in Xcode 12 or manually in the terminal using the following commands:

$ cd ./Scheme-Swift
$ swift build
$ swift run

Syntax

syntax	symbol	example	result
define	define	(define a "value")
if	if	(if #t (display "true") (display "false"))	true
set	set!	(set! a "new value")
begin	begin	(begin (define a 2) (+ 3 a))	5
lambda	lambda	((lambda (x y) (+ x y)) 1 2)	3
quote	quote	(quote 42)	42

Functions

function	symbol	type	example	result
addition	+	builtin	(+ 1 2 5)	8
subtraction	-	builtin	(- 10 5)	5
multiplication	*	builtin	(* 3 2)	6
division	/	builtin	(/ 5 2)	2.5
modulo	%	builtin	(% 5 2)	1
equal numbers	=	builtin	(= 1 11)	#f
equal objects	eq?	builtin	(eq? 1 1)	#t
greater than	>	builtin	(> 5 2)	#t
lesser than	<	builtin	(< 5 2)	#f
greater than or equal	>=	udf	(>= 5 5)	#t
lesser than or equal	<=	udf	(<= 5 5)	#t
display	display	builtin	(display "string")	displays string
print	print	builtin	(print "string")	displays "string"
truncate	truncate	builtin	(truncate 32.7)	displays 32
list	list	builtin	(list 1 2 3)	(1 2 3)
list	'	builtin	'(1 2 4 3)	(1 2 4 3)
cons	cons	builtin	(cons 5 '(4 3))	(5 4 3)
car	car	builtin	(car '(1 2 3))	1
cdr	cdr	builtin	(cdr '(1 2 3))	(2 3)
load	load	builtin	(load "absolute path to file")	Executes all statements in the file.
equal strings	string=?	builtin	(string=? "a" "a")	#t
char in string	string-ref	builtin	(string-ref "Hallo" 4)	'o'
append strings	string-append	builtin	(string-append "Hallo" "..." "!")	"Hallo...!"
length of string	string-length	builtin	(string-length "Hallo")	5
is string	string?	builtin	(string? "asd")	#t
is number	number?	builtin	(number? 0)	#t
is cons	cons?	builtin	(cons? '(1 2 3))	#t
is function	function?	builtin	(function? +)	#t
is function	builtin-funciton?	builtin	(builtin-funciton? +)	#t
is user defined function	user-function?	builtin	(user-function? +)	#f
is bool value	bool?	builtin	(bool? #f)	#t
power of n	pow	udf	(pow 10 3)	1000
factorial	factorial	udf	(factorial 4)	24
fibonacci	fibonacci	udf	(fibonacci 10)	55