Functional programming -- 2009-2010 -- info.uvt.ro/Laboratory/Notes 2

person

(define a 5)
(define b 7)
(print (if (> a b) a b))

int a = 5;
int b = 7;
System.out.println ((a > b) ? a : b);

a = 5
b = 7
print a if a > b else b

A = 5,
B = 7,
io:format ("~p~n", [if A > B -> A; true -> B end]).

(compute-something
    (let ((value (get-value)))
        (if (null? value) default-value value)))

compute_something (
    case get_value () of
        null -> DefaultValue;
        Value -> Value
    end).

Type v = getValue ();
computeSomething ((v != null) ? v : defaultValue);

(define s ... obtain socket ...)
(listen s
    (let ((port (get-env "port")))
        (cond
            ((eq? port null) 9999)
            ((convert-to-int port))
            (#t 9999))))

(define a '(1 2 3))
(define b '(4 5 6))
(print (for/list ((i a) (j b)) (+ i j)))

a = [1, 2, 3]
b = [4, 5, 6]
print [i + j for i, j in zip (a, b)]

A = [1, 2, 3],
B = [4, 5, 6],
io:format ("~p~n", [ [I + J || {I, J} <- lists:zip (A, B)] ]).

(define persons ... obtain the persons list ...)
(combo-set-labels! combo
    (sort (for/list ((p persons)) (person-get-name p))))

(define persons ... obtain the persons list ...)
(combo-set-labels-! combo (sort (map person-get-name persons)))

persons = ... obtain the persons list ...
combo.set_labels (sorted (map (lambda p : p.name, persons))

List<Persons> persons = ... obtain the persons list ...;
List<Names> names = new ArrayList<String> ();
for (Person person : persons)
    names.append (person.getName ());
names = Collections.sort (names);
combo.setLabels (names);

(define (compute a b)
    (values (+ a b) (* a b) (/ a b)))

(define-values (s p f) (compute 1 2))
(print (list s p f))

Compute = fun (A, B) ->
    {A + B, A * B, A / B} end,

{S, P, F} = Compute (1, 2),
io:format ("~p ~p ~p~n", [S, P, F]).

def compute (a, b) :
    return a + b, a * b, a / b

s, p, f = compute (1, 2)
print s, p, f

int[] compute (int a, int b) {
    return new int[] {a + b, a * b, a / b};
}

...
int[] o = compute (1, 2)
s = o[0]
p = o[1]
f = o[2]
System.out.format ("%d %d %d", s, p, f);

void compute (int a, int b, int *s, int *p, int *f) {
    *s = a + b;
    *p = a + b;
    *f = a / b;
}

Object[] compute (/* arguments */) {
    return Object[] {/* compute first value */, /* compute second value */};
}

...
Object[] o = compute (/* arguments */)
// we must use a casts
TypeA a = (TypeA) o[0];
TypeB b = (TypeB) o[1];

class Outcome {
    public Outcome (TypeA a, TypeB b) {
        this.a = a;
        this.b = b;
    }
    public TypeA a;
    public TypeB b;
}

Outcome compute (/* arguments */) {
    return new Outcome (/* compute first value */, /* compute second value */);
}

...
Outcome o = compute (/* arguments */);

class Triplet<TypeA, TypeB, TypeC> {
    public Outcome (TypeA a, TypeB b, TypeC c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
    public TypeA a;
    public TypeB b;
    public TypeC c;
}

Outcome compute (/* arguments */) {
    return new Triplet<MyTypeA, MyTypeB, MyTypeC> (/* compute first value of TypeA */, /* compute second value */, ...);
}

...
Triplet<TypeA, TypeB, TypeC> o1 = compute (/* arguments */);
Triplet<TypeA, TypeB, TypeC> o2 = compute (/* arguments */); // let's just assume we need two of this outcomes

(defun get-value (database key &optional (default nil))
    ...)

; ssn is Social Security Number (CNP in Romania)
(print (get-value persons ssn))
(print (get-value persons ssn "not-found"))

(define (get-value database key (default null))
    ...)

(print (get-value persons ssn))
(print (get-value persons ssn "not-found"))

def get_value (database, key, default = None) :
    ...

print get_value (database, key, "not-found")

public Object getValue (Database database, Object key) {
    return getValue (database, key, null);
}

public Object getValue (Database database, Object key, Object default_) {
...
}

(defun download (url &key (stream null) (login null) (password null) (timeout 60))
    ...)

(download "http://my-server/some-secret" :login "me" :password "secret")
(download "http://my-server/?some-service-query" :timeout 6)

(define (download url #:stream (s null) #:login (l null) #:password (p null) #:timeout (t 60))
    ...)

(download "http://my-server/some-secret" #:login "me" #:password "secret")
(download "http://my-server/?some-service-query" #:timeout 6)

def download (url, stream = sys.stdout, login = None, password = None, timeout = 60) :
    ...

download ("http://www.google.com", stream = file ("/tmp/google.html", "w"))
download ("http://my-server/?some-service-query", timeout = 6, login = "me", password = "secret")

(defun std-dev (&rest values)
    ...)

(print (std-dev 1 2 3 4 5 6))

(define (std-dev . values)
    ...)

(print (std-dev 1 2 3 4 5 6))

def std_dev (*values) :
    ...

print std_dev (1, 2, 3, 4)

float std_dev (float ... values) {
    ...
}

Functional programming -- 2009-2010 -- info.uvt.ro/Laboratory/Notes 2

Covered topics

Examples

Control structures as expressions

Multiple return values

Function arguments

Exercises

References

Reading

API