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@theodesp
Last active August 22, 2018 11:35
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Scheme Reference #scheme
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
;; Make a variable `call/cc' an alias of `call-with-current-continuation`.
(define call/cc call-with-current-continuation)
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
;; Local Variables and Environments
(define a 5.3)
(define b 4.7)
(define c 2.8)
(define area
(let ((s (/ (+ a b c) 2)))
(sqrt (* s (- s a) (- s b) (- s c)))))
;; Lexixal Scoping
(define currency-abbreviation "USD")
(define (currency-string units hundredths)
(string-append currency-abbreviation
(number->string units)
"."
(number->string hundredths)))
(define (french-currency-string units hundredths)
(let ((currency-abbreviation "FRF"))
(currency-string units hundredths)))
(french-currency-string 33 44) ; "USD33.44" as `currency-abbreviation` inside `currency-string` is taken from the global environment
(define (make-serial-number-generator)
(let ((current-serial-number 0))
(lambda ()
(set! current-serial-number (+ current-serial-number 1))
current-serial-number)))
(define entry-sn-generator (make-serial-number-generator))
(entry-sn-generator) ; 1
(entry-sn-generator) ; 2
;; Example with A Shared Persistent Variable
(define get-balance #f)
(define deposit #f)
(let ((balance 0))
(set! get-balance
(lambda ()
balance))
(set! deposit
(lambda (amount)
(set! balance (+ balance amount))
balance)))
(define (withdraw amount)
(deposit (- amount)))
(get-balance) ; 0
(deposit 50) ; 50
(withdraw 75) ; -25
;; Example: Object Orientation
(define (make-account)
(let ((balance 0))
(define (get-balance)
balance)
(define (deposit amount)
(set! balance (+ balance amount))
balance)
(define (withdraw amount)
(deposit (- amount)))
(lambda args
(apply
(case (car args)
((get-balance) get-balance)
((deposit) deposit)
((withdraw) withdraw)
(else (error "Invalid method!")))
(cdr args)))))
(define my-account (make-account))
(my-account 'get-balance) ; 0
(my-account 'withdraw 5) ; -5
(my-account 'deposit 396) ;391
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
;; A Scheme program consists of a sequence of expressions.
;; A Scheme interpreter executes the program by evaluating these expressions in order, one by one.
;; Evaluating Literal Data
"abc" ; string
3+4i ; complex number
#(1 2 3) ; vector
'() ; list
;; Evaluating a Variable Reference
(define key "Paul Smith")
(set! key 3.74)
(set! another 3.75) ;; error!
;; Evaluating a Procedure Invocation Expression
(string-length (string-append "/home" "/" "andrew"))
;; (string-length (string-append "/home" "/" "andrew") =>
;; (string-length "/home/andrew") => 12
;; Evaluating Special Syntactic Expressions
;; `If` needs to be evaluated before we delete the file. `If` is a special syndax.
(if (string=? (read-answer "Should I delete this file?")
"yes")
(delete-file file))
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
; Define module with list of exports
(define-module (foo bar)
#:export (times-2))
(define (times-2 x) (* 2 x))
(begin
(display (times-2 10))
(newline))
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
;; A procedure invocation in Scheme is written like this:
;; (procedure [arg1 [arg2 …]])
(string-append "/home" "/" "andrew") ;; "/home/andrew"
;; Returns the length of a single string argument,
(string-length "abc") ;; 3
;; Creating
;; (lambda (name address) expression …)
;; Invocation
((lambda (name address)
(string-append "Name=" name ":Address=" address))
"FSF"
"Cambridge")
;; Return a function
(define make-combined-string
(lambda (name address)
(string-append "Name=" name ":Address=" address)))
(make-combined-string "FSF" "Cambridge") ;; "Name=FSF:Address=Cambridge"
;; A define expression of the form
;; (define (name [arg1 [arg2 …]])
;; expression …)
;; is exactly equivalent to the longer form
;; (define name
;; (lambda ([arg1 [arg2 …]])
;; expression …))
;; Variadic arguments
(define (square-var x . rest)
(* x (car rest)))
(square-var 5 6 7 8) ;; 30
(import (rnrs (6)))
(use-modules ((rnrs) :version (6)))
;; Make a variable `x' with initial numeric value 1.
(define x 1)
;; Make a variable `organization' with an initial string value.
(define organization "Free Software Foundation")
;; Change the value of `x' to 5.
(set! x 5)
;; Change the value of `organization' to the FSF's street number.
(set! organization 545)
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