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[racket/en] Add more details about Racket (#2278)
* Add let* and letrec reference * More elaboration on structs * Add code about predefined car, cdr functions * Mention explicit typing, int to real conversion
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@ -114,18 +114,42 @@ some-var ; => 5
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"Alice"
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me) ; => "Bob"
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;; let* is like let, but allows you to use previous bindings in creating later bindings
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(let* ([x 1]
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[y (+ x 1)])
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(* x y))
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;; finally, letrec allows you to define recursive and mutually recursive functions
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(letrec ([is-even? (lambda (n)
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(or (zero? n)
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(is-odd? (sub1 n))))]
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[is-odd? (lambda (n)
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(and (not (zero? n))
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(is-even? (sub1 n))))])
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(is-odd? 11))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; 3. Structs and Collections
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Structs
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; By default, structs are immutable
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(struct dog (name breed age))
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(define my-pet
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(dog "lassie" "collie" 5))
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my-pet ; => #<dog>
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; returns whether the variable was constructed with the dog constructor
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(dog? my-pet) ; => #t
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; accesses the name field of the variable constructed with the dog constructor
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(dog-name my-pet) ; => "lassie"
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; You can explicitly declare a struct to be mutable with the #:mutable option
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(struct rgba-color (red green blue alpha) #:mutable)
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(define burgundy
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(rgba-color 144 0 32 1.0))
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(set-color-green! burgundy 10)
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(color-green burgundy) ; => 10
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;;; Pairs (immutable)
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;; `cons' constructs pairs, `car' and `cdr' extract the first
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;; and second elements
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@ -143,6 +167,16 @@ my-pet ; => #<dog>
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;; and a quote can also be used for a literal list value
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'(1 2 3) ; => '(1 2 3)
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;; Racket has predefined functions on top of car and cdr, to extract parts of a list
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(cadr (list 1 2 3)) ; => 2
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(car (cdr (list 1 2 3))) ; => 2
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(cddr (list 1 2 3)) ; => '(3)
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(cdr (cdr (list 1 2 3))) ; => '(3)
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(caddr (list 1 2 3)) ; => 3
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(car (cdr (cdr (list 1 2 3)))) ; => 3
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;; Can still use `cons' to add an item to the beginning of a list
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(cons 4 '(1 2 3)) ; => '(4 1 2 3)
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@ -24,6 +24,12 @@ val phone_no = 5551337
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val pi = 3.14159
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val negative_number = ~15 (* Yeah, unary minus uses the 'tilde' symbol *)
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(* Optionally, you can explicitly declare types. This is not necessary as
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ML will automatically figure out the types of your values. *)
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val diameter = 7926 : int
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val e = 2.718 : real
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val name = "Bobby" : string
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(* And just as importantly, functions: *)
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fun is_large(x : int) = if x > 37 then true else false
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@ -31,6 +37,8 @@ fun is_large(x : int) = if x > 37 then true else false
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val tau = 2.0 * pi (* You can multiply two reals *)
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val twice_rent = 2 * rent (* You can multiply two ints *)
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(* val meh = 1.25 * 10 *) (* But you can't multiply an int and a real *)
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val yeh = 1.25 * (Real.fromInt 10) (* ...unless you explicitly convert
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one or the other *)
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(* +, - and * are overloaded so they work for both int and real. *)
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(* The same cannot be said for division which has separate operators: *)
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