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+---
+language: "Scheme" 
+filename: scheme.scm 
+contributors:
+- ["Bruno Ciccarino", "https://github.com/BrunoCiccarino"]
+---
+
+Scheme is a minimalist dialect of Lisp that is widely used in education, research, and industry. It emphasizes simplicity, powerful abstractions, and functional programming paradigms.
+
+A classic resource to learn Scheme is [Structure and Interpretation of Computer Programs (SICP)](https://web.mit.edu/6.001/6.037/sicp.pdf). For a modern introduction, consider [The Scheme Programming Language](https://www.scheme.org/).
+
+```scheme
+;;;-----------------------------------------------------------------------------
+;;; 0. Syntax
+;;;-----------------------------------------------------------------------------
+
+;;; General form
+
+;;; Scheme has two fundamental elements of syntax: ATOM and S-EXPRESSION.
+;;; S-expressions are used for both data and code.
+
+10          ; a number atom; evaluates to itself
+'symbol     ; a symbol atom; evaluates to itself when quoted
+#t          ; boolean true
+(+ 1 2 3)   ; an s-expression (function application)
+'(4 'foo #t) ; quoted s-expression (a list)
+
+
+;;; Comments
+
+;;; Single-line comments start with a semicolon:
+; This is a single-line comment
+
+;;; Block comments use `#|` and `|#`:
+#| This is a block comment.
+   It spans multiple lines.
+|#
+
+
+;;; REPL and environment
+
+;;; Scheme is typically developed interactively in a Read-Eval-Print Loop (REPL). 
+;;; Implementations such as Racket, Guile, or MIT Scheme provide REPLs for interactive exploration.
+;;; Libraries and tools can be installed depending on the specific implementation.
+
+
+
+;;;-----------------------------------------------------------------------------
+;;; 1. Primitive datatypes and operators
+;;;-----------------------------------------------------------------------------
+
+;;; Numbers
+
+42          ; integers
+#b101       ; binary => 5
+#o777       ; octal => 511
+#xFF        ; hexadecimal => 255
+3.14        ; floating-point numbers
+1/2         ; fractions (exact rational numbers)
+(make-rectangular 1 2) ; complex numbers
+
+
+;;; Basic arithmetic
+
+(+ 1 2)     ; => 3
+(- 7 3)     ; => 4
+(* 2 5)     ; => 10
+(/ 10 3)    ; => 10/3
+(sqrt 4)    ; => 2
+(expt 2 3)  ; => 8
+
+
+;;; Booleans
+
+#t          ; true
+#f          ; false
+(and #t #f) ; => #f
+(or #t #f)  ; => #t
+(not #t)    ; => #f
+
+
+;;; Strings
+
+"Hello, World!"
+(string-append "Hello, " "World!") ; => "Hello, World!"
+
+
+;;; Lists
+
+'(1 2 3)      ; a list
+(cons 1 '(2 3)) ; => '(1 2 3)
+(car '(1 2 3))  ; => 1
+(cdr '(1 2 3))  ; => '(2 3)
+(append '(1 2) '(3 4)) ; => '(1 2 3 4)
+
+
+;;;-----------------------------------------------------------------------------
+;;; 2. Variables
+;;;-----------------------------------------------------------------------------
+
+;;; Define a variable
+
+(define x 10)
+x           ; => 10
+
+
+;;; Define a local variable
+
+(let ((x 5)) (+ x 10)) ; => 15
+x                      ; => 10 (unchanged globally)
+
+
+;;;-----------------------------------------------------------------------------
+;;; 3. Functions
+;;;-----------------------------------------------------------------------------
+
+;;; Define a named function
+
+(define (square x)
+  (* x x))
+
+(square 4) ; => 16
+
+
+;;; Define an anonymous (lambda) function
+
+((lambda (x) (* x x)) 5) ; => 25
+
+
+;;; Higher-order functions
+
+(define (apply-twice f x)
+  (f (f x)))
+
+(apply-twice square 2) ; => 16
+
+
+;;;-----------------------------------------------------------------------------
+;;; 4. Conditionals and control flow
+;;;-----------------------------------------------------------------------------
+
+;;; If statements
+
+(if (> 5 3)
+    'yes
+    'no)     ; => 'yes
+
+
+;;; Cond expressions (multi-branch conditionals)
+
+(cond
+  [(< 5 3) 'less]
+  [(> 5 3) 'greater]
+  [else 'equal]) ; => 'greater
+
+
+;;;-----------------------------------------------------------------------------
+;;; 5. Structs and collections
+;;;-----------------------------------------------------------------------------
+
+;;; Define a structure
+
+(define-struct dog (name breed age))
+
+(define my-dog (make-dog "Fido" "Labrador" 5))
+
+(dog-name my-dog)   ; => "Fido"
+(dog-age my-dog)    ; => 5
+
+
+;;;-----------------------------------------------------------------------------
+;;; 6. Common patterns
+;;;-----------------------------------------------------------------------------
+
+;;; Recursive functions
+
+(define (factorial n)
+  (if (= n 0)
+      1
+      (* n (factorial (- n 1)))))
+
+(factorial 5) ; => 120
+
+
+;;;-----------------------------------------------------------------------------
+;;; 7. Libraries and modules
+;;;-----------------------------------------------------------------------------
+
+;;; Importing libraries/modules depends on the implementation.
+;;; For example, in Racket:
+
+(require racket/math)
+
+(sqrt 16) ; => 4
+
+;;;-----------------------------------------------------------------------------
+;;; 8. Macros
+;;;-----------------------------------------------------------------------------
+
+;;; Macros allow you to create new syntactic constructs.
+
+(define-syntax when
+  (syntax-rules ()
+    [(when test body ...)
+     (if test
+         (begin body ...))]))
+
+(when #t
+  (display "Condition is true!\n")) ; Output: Condition is true!
+
+
+;;;-----------------------------------------------------------------------------
+;;; 9. Input and Output (I/O)
+;;;-----------------------------------------------------------------------------
+
+;;; Printing to the console
+
+(display "Hello, Scheme!") ; => prints "Hello, Scheme!"
+(newline)                  ; => moves to the next line
+
+
+;;; Reading input
+
+(let ((user-input (read)))
+  (display "You entered: ")
+  (display user-input))
+
+
+;;; File I/O
+
+(define output-port (open-output-file "example.txt"))
+(display "Writing to a file." output-port)
+(close-output-port output-port)
+
+(define input-port (open-input-file "example.txt"))
+(let ((file-content (read input-port)))
+  (display file-content))
+(close-input-port input-port)
+
+
+;;;-----------------------------------------------------------------------------
+;;; 10. Iteration
+;;;-----------------------------------------------------------------------------
+
+;;; Iterating with `do`
+
+(do ((i 0 (+ i 1)))        ; initialize i to 0, increment by 1
+    ((>= i 5))             ; stop when i >= 5
+  (display i)              ; print i
+  (newline))
+
+
+;;; Using recursion for iteration
+
+(define (countdown n)
+  (if (= n 0)
+      (display "Blastoff!\n")
+      (begin
+        (display n)
+        (newline)
+        (countdown (- n 1)))))
+
+(countdown 5) ; Output: 5 4 3 2 1 Blastoff!
+
+
+;;;-----------------------------------------------------------------------------
+;;; 11. Error handling
+;;;-----------------------------------------------------------------------------
+
+;;; Using `guard` for error handling (Racket example)
+
+(guard [e (displayln (format "Error: ~a" e))]
+  (/ 1 0)) ; Output: Error: division by zero
+
+
+;;; Catching exceptions manually
+
+(with-handlers ([exn:fail? (lambda (e) (displayln "Caught an error!"))])
+  (error "Something went wrong!")) ; Output: Caught an error!
+
+
+;;;-----------------------------------------------------------------------------
+;;; 12. Advanced concepts
+;;;-----------------------------------------------------------------------------
+
+;;; Continuations with `call/cc`
+
+(call/cc
+ (lambda (cont)
+   (display "Before continuation\n")
+   (cont #f)
+   (display "After continuation\n"))) ; Output: Before continuation
+
+
+;;; Lazy evaluation (streams)
+
+(define (make-stream start step)
+  (cons start
+        (lambda () (make-stream (+ start step) step))))
+
+(define nums (make-stream 0 1)) ; Infinite stream starting at 0, incrementing by 1
+
+(define (stream-ref stream n)
+  (if (= n 0)
+      (car stream)
+      (stream-ref ((cdr stream)) (- n 1))))
+
+(stream-ref nums 5) ; => 5
+
+
+;;;-----------------------------------------------------------------------------
+;;; 13. Meta-programming
+;;;-----------------------------------------------------------------------------
+
+;;; Evaluate expressions dynamically
+
+(eval '(+ 1 2)) ; => 3
+
+
+;;; Quasiquoting for meta-programming
+
+`(1 2 ,(+ 3 4)) ; => '(1 2 7)
+
+```