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Programming-Idioms

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Idiom #27 Create a 3-dimensional array

Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.

 


my $array3d = [
    [ [ 1, 0, 1 ],
      [ 0, 0, 0 ],
      [ 1, 0, 1 ] ],
    [ [ 0, 0, 0 ],
      [ 0, 2, 0 ],
      [ 0, 0, 0 ] ],
    [ [ 3, 0, 3, ],
      [ 0, 0, 0, ],
      [ 3, 0, 3, ] ]
];

Idiom #127 Source code inclusion

Import the source code for the function foo body from a file "foobody.txt".

 


sub foo {
    do './foobody.txt';
}

Idiom #200 Return hypotenuse

Compute the hypotenuse h of the triangle where the sides adjacent to the square angle have lengths x and y.

 


my $h = hypot $x, $y;

For many more Perl snippets to curate, see the full list.

Docs & demos

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45% of the Perl snippets don't have an external link to a documentation page yet. For example, these implementations would need a doc URL:

Idiom #80 Truncate floating point number to integer

Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x .
Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).

 

my $y = int($x);

Idiom #67 Binomial coefficient "n choose k"

Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.

 

sub binom {
   my ($n, $k) = @_;
   my $fact = sub {
      my $n = shift;
      return $n<2 ? 1 : $n * $fact->($n-1);
   };
   return $fact->($n) / ($fact->($k) * ($fact->($n-$k)));
}

Idiom #117 Get list size

Set n to the number of elements of the list x.

 

my $N = @x;

75% of the Perl snippets don't have a runnable demo yet.

For example, these implementations would need a demo URL:

Idiom #209 Type with automatic deep deallocation

Declare a type t which contains a string s and an integer array n with variable size, and allocate a variable v of type t. Allocate v.s and v.n and set them to the values "Hello, world!" for s and [1,4,9,16,25], respectively. Deallocate v, automatically deallocating v.s and v.n (no memory leaks).

 

class T {
    has 's', is => 'ro', isa => Str;
    has 'n', is => 'ro', isa => ArrayRef[Int];
}

{
    my $v = T->new(s => 'Hello, world!', n => [1,4,9,16,25]);
    # deallocation happens at closing brace, see explanation
}

Idiom #3 Create a procedure

Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)

 

sub some_procedure {
    print 'some side effect';
    return;
}

Idiom #7 Iterate over list indexes and values

Print each index i with its value x from an array-like collection items

 

while (my ($i, $x) = each @items) {
    print "array[$i] = $x\n";
}

Missing implementations

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A Perl implementation is missing for 12 idioms out of 344 idioms.

You may help by writing a Perl snippet for these idioms:


Idiom #341 Find substring last position

Set i to the position of the last occurrence of the string y inside the string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.

Idiom #342 Leap year?

Determine if the current year is a leap year.

Idiom #345 Convert string to big integer

Create the integer value i initialized from its string representation s (in radix 10)

Use an integer type that can hold huge values. Explain what happens if s cannot be parsed.