diff options
| -rw-r--r-- | racket.html.markdown | 34 | ||||
| -rw-r--r-- | standard-ml.html.markdown | 8 |
2 files changed, 42 insertions, 0 deletions
diff --git a/racket.html.markdown b/racket.html.markdown index 0fe3f030..96dcaf25 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -114,18 +114,42 @@ some-var ; => 5 "Alice" me) ; => "Bob" +;; let* is like let, but allows you to use previous bindings in creating later bindings +(let* ([x 1] + [y (+ x 1)]) + (* x y)) + +;; finally, letrec allows you to define recursive and mutually recursive functions +(letrec ([is-even? (lambda (n) + (or (zero? n) + (is-odd? (sub1 n))))] + [is-odd? (lambda (n) + (and (not (zero? n)) + (is-even? (sub1 n))))]) + (is-odd? 11)) + ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; 3. Structs and Collections ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Structs +; By default, structs are immutable (struct dog (name breed age)) (define my-pet (dog "lassie" "collie" 5)) my-pet ; => #<dog> +; returns whether the variable was constructed with the dog constructor (dog? my-pet) ; => #t +; accesses the name field of the variable constructed with the dog constructor (dog-name my-pet) ; => "lassie" +; You can explicitly declare a struct to be mutable with the #:mutable option +(struct rgba-color (red green blue alpha) #:mutable) +(define burgundy + (rgba-color 144 0 32 1.0)) +(set-color-green! burgundy 10) +(color-green burgundy) ; => 10 + ;;; Pairs (immutable) ;; `cons' constructs pairs, `car' and `cdr' extract the first ;; and second elements @@ -143,6 +167,16 @@ my-pet ; => #<dog> ;; and a quote can also be used for a literal list value '(1 2 3) ; => '(1 2 3) +;; Racket has predefined functions on top of car and cdr, to extract parts of a list +(cadr (list 1 2 3)) ; => 2 +(car (cdr (list 1 2 3))) ; => 2 + +(cddr (list 1 2 3)) ; => '(3) +(cdr (cdr (list 1 2 3))) ; => '(3) + +(caddr (list 1 2 3)) ; => 3 +(car (cdr (cdr (list 1 2 3)))) ; => 3 + ;; Can still use `cons' to add an item to the beginning of a list (cons 4 '(1 2 3)) ; => '(4 1 2 3) diff --git a/standard-ml.html.markdown b/standard-ml.html.markdown index 143980e7..133e4f54 100644 --- a/standard-ml.html.markdown +++ b/standard-ml.html.markdown @@ -24,6 +24,12 @@ val phone_no = 5551337 val pi = 3.14159 val negative_number = ~15 (* Yeah, unary minus uses the 'tilde' symbol *) +(* Optionally, you can explicitly declare types. This is not necessary as + ML will automatically figure out the types of your values. *) +val diameter = 7926 : int +val e = 2.718 : real +val name = "Bobby" : string + (* And just as importantly, functions: *) fun is_large(x : int) = if x > 37 then true else false @@ -31,6 +37,8 @@ fun is_large(x : int) = if x > 37 then true else false val tau = 2.0 * pi (* You can multiply two reals *) val twice_rent = 2 * rent (* You can multiply two ints *) (* val meh = 1.25 * 10 *) (* But you can't multiply an int and a real *) +val yeh = 1.25 * (Real.fromInt 10) (* ...unless you explicitly convert + one or the other *) (* +, - and * are overloaded so they work for both int and real. *) (* The same cannot be said for division which has separate operators: *) |