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Kristopher Paulsen
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NAME

Sub::Fp - A Clojure / Python Toolz / Lodash inspired Functional Utility Library

SYNOPSIS

This library provides numerous functional programming utility methods, as well as functional varients of native in-built methods, to allow for consistent, concise code.

SUBROUTINES/METHODS

Self Partialing: The __ function

Sub::Fp has a "special" function, the __ placeholder. This function allows for "self partialing", which is similar to auto-currying in many functional languages. This works for every single function in the Sub::Fp library, except for flow flow_right partial chain

    # TLDR

    my $person = { name => "Sally" };

    my $get_name = get('{name}', __);  # <---- Function uses placeholder to "self-partial", and return new sub

    print $get_name->($person);        # <---- Invoke function with argument

    # "Sally"

That's it! It also works with multiple placeholders, in different positions, with different permutations of supplied arguments.

    my $range = range(__, __);

    print Dumper($range->(1, 10));

    # [1,2,3,4,5,6,7,8,9]


    my $range = range(__, __, __);

    print Dumper($range->(1, 4, 0));

    # [1,1,1,1];



    my $range = range(__, 4, __);

    print Dumper($range->(1, 0));

    # [1,1,1,1];

Prior Art: This is not a new concept by any means (I'm just stealing it), and it's existed in functional languages for well over half a century. Its a natural application of functional composition. To get a better feel for what it looks like in other languages see:

1. thread-as macro in Clojure

2. Partialing in Lodash, PyToolz etc

3. Auto Currying in Haskell, Lodash-Fp, Ramda, Elm

4. The use of _ in languages as a placeholder. This library uses double underscore instead to differentiate it from the native library, which already uses a single underscore in some circumstances.

EXPORT

    incr         reduces   flatten
    drop_right  drop      take_right  take
    assoc       maps      decr        chain
    first       end       subarray    partial
    __          find      filter      some
    none        uniq      bool        spread   every
    len         is_array  is_hash     to_keys  to_vals
    noop        identity  is_empty    flow     eql
    is_sub      to_pairs  for_each    apply
    get         second

incr

Increments the supplied number by 1

    incr(1)

    # 2

decr

Decrements the supplied number by 1

    decr(2)

    # 1

once

Creates a function that is restricted to invoking func once. Repeat calls to the function return the value of the first invocation.

    my $times_called = 0;
    my $sub          = once(sub {
        $times_called++;
        return "I was only called $times_called time"
    });

    $sub->(); # "I was only called 1 time"
    $sub->(); # "I was only called 1 time"
    $sub->(); # etc

apply

Calls the supplied function with the array of arguments, spreading the arguments into the function it invokes

    my $sum_all_nums = sub {
        my $num        = shift;
        my $second_num = shift;

        return $num + $second_num;
    };

    apply($sum_all_nums, [100, 200]);
    # same as $sum_all_nums->(100, 200)

    # 300

range

Creates an array of numbers (positive and/or negative) progressing from start up to, but not including, end. A step of -1 is used if a negative start is specified without an end or step. If end is not specified, it's set to start with start then set to 0.

    range(10);

    # [1,2,3,4,5,6,7,8,9]


    range(1,10);

    # [1,2,3,4,5,6,7,8,9]

    range(-1, -10);

    # [-1, -2, -3, -4, -5, -6 ,-7, -8, -9]

    range(1, 4, 0);

    # [1, 1, 1]


    #Ranges that "dont make sense" will return empty arrays

    range(-1, -4, 0);

    # []

    range(100, 1, 0)

    # []

    range(0,0,0)

    # []

    range(0, -100, 100)

    # []

    range(0, 100, -100)

    # []

    #etc...

for_each

Iterates over elements of collection and invokes iteratee for each element. The iteratee is invoked with three arguments: (value, index|key, collection).

    for_each(sub {
       my $num = shift;
       print $num;
    }, [1,2,3]);


    for_each(sub {
       my ($num, $idx, $coll) = @_;
       print $idx;
    }, [1,2,3])

    # 0 1 2

    for_each(sub {
       my ($num, $idx, $coll) = @_;
       print Dumper $coll;
    }, [1,2,3])

    #   [1,2,3],
    #   [1,2,3],
    #   [1,2,3]

maps

Creates an array of values by running each element in collection thru iteratee. The iteratee is invoked with three arguments: (value, index|key, collection).

    maps(sub {
        my $num = shift;
        return $num + 1;
    }, [1,1,1]);

    # [2,2,2]

reduces

Reduces collection to a value which is the accumulated result of running each element in collection thru iteratee, where each successive invocation is supplied the return value of the previous. If accumulator is not given, the first element of collection is used as the initial value. The iteratee is invoked with four arguments: (accumulator, value, index|key, collection).

    # Implicit Accumulator

    reduces(sub {
        my ($sum, $num) = @_;

        return $sum + $num;
    }, [1,1,1]);

    # 3


    # Explict Accumulator

    reduces(sub {
        my ($accum, $num) = @_;
        return {
            spread($accum),
            key => $num,
        }
    }, {}, [1,2,3]);

    # {
    #    key => 1,
    #    key => 2,
    #    key => 3,
    # }

flatten

Flattens array a single level deep.

    flatten([1,1,1, [2,2,2]]);

    # [1,1,1,2,2,2];

pop / pushes / shifts / unshifts

Works the same as builtin pop / push etc etc, with mutations, except it uses references instead of @ lists.

    my $array = [1,2,3];

    pops($array)

    # 3

    my $array = [1,2,3];

    pushes($array, 4);

    # [1,2,3,4]

drop

Creates a slice of array with n elements dropped from the beginning.

    drop([1,2,3])

    # [2,3];

    drop(2, [1,2,3])

    # [3]

    drop(5, [1,2,3])

    # []

    drop(0, [1,2,3])

    # [1,2,3]

drop_right

Creates a slice of array with n elements dropped from the end.

    drop_right([1,2,3]);

    # [1,2]

    drop_right(2, [1,2,3])

    # [1]

    drop_right(5, [1,2,3])

    # []

    drop_right(0, [1,2,3])

    #[1,2,3]

take

Creates a slice of array with n elements taken from the beginning.

    take([1, 2, 3);

    # [1]

    take(2, [1, 2, 3]);

    # [1, 2]

    take(5, [1, 2, 3]);

    # [1, 2, 3]

    take(0, [1, 2, 3]);

    # []

take_right

Creates a slice of array with n elements taken from the end.

    take_right([1, 2, 3]);

    # [3]

    take_right(2, [1, 2, 3]);

    # [2, 3]

    take_right(5, [1, 2, 3]);

    # [1, 2, 3]

    take_right(0, [1, 2, 3]);

    # []

second

Returns the second item in an array

    second(["I", "am", "a", "string"])

    # "am"

    second([5,4,3,2,1])

    # 4

first

Returns the first item in an array

    first(["I", "am", "a", "string"])

    # "I"

    first([5,4,3,2,1])

    # 5

end

Returns the end, or last item in an array

    end(["I", "am", "a", "string"])

    # "string"

    end([5,4,3,2,1])

    # 1

len

Returns the length of the collection. If an array, returns the number of items. If a hash, the number of key-val pairs. If a string, the number of chars (following built-in split)

    len([1,2,3,4])

    # 4

    len("Hello")

    # 5

    len({ key => 'val', key2 => 'val'})

    #2

    len([])

    # 0

noop

A function that does nothing (like our government), and returns undef

    noop()

    # undef

identity

A function that returns its first argument

    identity()

    # undef

    identity(1)

    # 1

    identity([1,2,3])

    # [1,2,3]

eql

Returns 0 or 1 if the two values have == equality, with convience wrapping for different types (no need to use eq vs ==). Follows internal perl rules on equality following strings vs numbers in perl.

    eql([], [])

    # 1

    eql(1,1)

    # 1


    my $obj = {};

    eql($obj, $obj);

    # 1


    eql("123", 123)

    # 1  'Following perls internal rules on comparing scalars'


    eql({ key => 'val' }, {key => 'val'});

    # 0 'Only identity equality'

is_sub

Returns 0 or 1 if the argument is a sub ref

    is_sub()

    # 0

    is_sub(sub {})

    # 1

    my $sub = sub {};
    is_sub($sub)

    # 1

is_array

Returns 0 or 1 if the argument is an array

    is_array()

    # 0

    is_array([1,2,3])

    # 1

is_hash

Returns 0 or 1 if the argument is a hash

    is_hash()

    # 0

    is_hash({ key => 'val' })

    # 1

is_empty

Returns 1 if the argument is 'empty', 0 if not empty. Used on strings, arrays, hashes.

    is_empty()

    # 1

    is_empty([])

    # 1

    is_empty([1,2,3])

    # 0

    is_empty({ key => 'val' })

    # 0

    is_empty("I am a string")

    # 0

get

Returns value from hash, string, array based on key/idx provided. Returns default value if provided key/idx does not exist on collection. Only works one level deep;

    my $hash = {
        key1 => 'value1',
    };

    get('key1', $hash);

    # 'value1'


    my $array = [100, 200, 300]

    get(1, $array);

    # 200


    my $string = "Hello";

    get(1, $string);

    # e


    # Also has the ability to supply default-value when key/idx does not exist

    my $hash = {
        key1 => 'value1',
    };

    get('key2', $hash, "DEFAULT HERE");

    # 'DEFAULT HERE'

spread

Destructures an array / hash into non-ref context. Destructures a string into an array of chars (following in-built split)

    spread([1,2,3,4])

    # 1,2,3,4

    spread({ key => 'val' })

    # key,'val'

    spread("Hello")

    # 'H','e','l','l','o'

bool

Returns 0 or 1 based on truthiness of argument, following internal perl rules based on ternary coercion

    bool([])

    # 1

    bool("hello!")

    # 1

    bool()

    # 0

    bool(undef)

    # 0

to_keys

Creates an array of the key names in a hash, indicies of an array, or chars in a string

    to_keys([1,2,3])

    # [0,1,2]

    to_keys({ key => 'val', key2 => 'val2' })

    # ['key', 'key2']

    to_keys("Hey")

    # [0, 1, 2];

to_vals

Creates an array of the values in a hash, of an array, or string.

    to_vals([1,2,3])

    # [0,1,2]

    to_vals({ key => 'val', key2 => 'val2' })

    # ['val', 'val2']

    to_vals("Hey");

    # ['H','e','y'];

to_pairs

Creates an array of key-value, or idx-value pairs from arrays, hashes, and strings. If used on a hash, key-pair order can not be guaranteed;

    to_pairs("I am a string");

    # [
    #  [0, "I"],
    #  [1, "am"],
    #  [2, "a"],
    #  [3, "string"]
    # ]

    to_pairs([100, 101, 102]);

    # [
    #  [0, 100],
    #  [1, 102],
    #  [2, 103],
    # ]

    to_pairs({ key1 => 'value1', key2 => 'value2' });

    # [
    #   [key1, 'value1'],
    #   [key2, 'value2']
    # ]

    to_pairs({ key1 => 'value1', key2 => { nested => 'nestedValue' }});

    # [
    #   [key1, 'value1'],
    #   [key2, { nested => 'nestedValue' }]
    # ]

uniq

Creates a duplicate-free version of an array, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array.

    uniq([2,1,2])

    # [2,1]

    uniq(["Hi", "Howdy", "Hi"])

    # ["Hi", "Howdy"]

assoc

Returns new hash, or array, with the updated value at index / key. Shallow updates only

    assoc([1,2,3,4,5,6,7], 0, "item")

    # ["item",2,3,4,5,6,7]

    assoc({ name => 'sally', age => 26}, 'name', 'jimmy')

    # { name => 'jimmy', age => 26}

subarray

Returns a subset of the original array, based on start index (inclusive) and end idx (not-inclusive)

    subarray(["first", "second", "third", "fourth"], 0,2)

    # ["first", "second"]

find

Iterates over elements of collection, returning the first element predicate returns truthy for.

    my $people = [
        {
            name => 'john',
            age => 25,
        },
        {
            name => 'Sally',
            age => 25,
        }
    ]

    find(sub {
        my $person = shift;
        return eql($person->{'name'}, 'sally')
    }, $people);

    # { name => 'sally', age => 25 }

filter

Iterates over elements of collection, returning only elements the predicate returns truthy for.

    my $people = [
        {
            name => 'john',
            age => 25,
        },
        {
            name => 'Sally',
            age => 25,
        },
        {
            name => 'Old Greg',
            age => 100,
        }
    ]

    filter(sub {
        my $person = shift;
        return $person->{'age'} < 30;
    }, $people);

    # [
    #    {
    #        name => 'john',
    #        age => 25,
    #    },
    #    {
    #        name => 'Sally',
    #        age => 25,
    #    }
    # ]

none

If one element is found to return truthy for the given predicate, none returns 0

    my $people = [
        {
            name => 'john',
            age => 25,
        },
        {
            name => 'Sally',
            age => 25,
        },
        {
            name => 'Old Greg',
            age => 100,
        }
    ]

    none(sub {
        my $person = shift;
        return $person->{'age'} > 99;
    }, $people);

    # 0

    none(sub {
        my $person = shift;
        return $person->{'age'} > 101;
    }, $people);

    # 1

every

Itterates through each element in the collection, and checks if element makes predicate return truthy. If all elements cause predicate to return truthy, every returns 1;

    every(sub {
        my $num = shift;
        $num > 0;
    }, [1,2,3,4]);

    # 1

    every(sub {
        my $num = shift;
        $num > 2;
    }, [1,2,3,4]);

    # 0

some

Checks if predicate returns truthy for any element of collection. Iteration is stopped once predicate returns truthy.

    some(sub {
        my $num = shift;
        $num > 0;
    }, [1,2,3,4]);

    # 1

    some(sub {
        my $num = shift;
        $num > 2;
    }, [1,2,3,4]);

    # 1

partial

Creates a function that invokes func with partials prepended to the arguments it receives. (funcRef, args)

    my $add_three_nums = sub {
        my ($a, $b, $c) = @_;

        return $a + $b + $c;
    };

    my $add_two_nums = partial($add_three_nums, 1);

    $add_two_nums->(1,1)

    # 3


    # Can also use __ to act as a placeholder

    my $add_four_strings = sub {
        my ($a, $b, $c, $d) = @_;

        return $a . $b . $c . $d;
    };

    my $add_two_strings = partial($add_four_strings, "first ", __, "third ", __);

    $add_two_strings->("second ", "third ")

    # "first second third fourth"

chain

Composes functions, left to right, and invokes them, returning the result. Accepts an expression as the first argument, to be passed as the first argument to the proceding function

    chain(
        [1,2,3, [4,5,6]],
        sub {
            my $array = shift;
            return [spread($array), 7]
        },
        \&flatten,
    );

    # [1,2,3,4,5,6,7]


    # Invokes first function, and uses that as start value for next func
    chain(
        sub { [1,2,3, [4,5,6]] },
        sub {
            my $array = shift;
            return [spread($array), 7]
        },
        \&flatten,
    )

    # [1,2,3,4,5,6,7]

flow

Creates a function that returns the result of invoking the given functions, where each successive invocation is supplied the return value of the previous.

    my $addTwo = flow(\&incr, \&incr);

    $addTwo->(1);

    # 3

AUTHOR

Kristopher C. Paulsen, <kristopherpaulsen+cpan at gmail.com>

BUGS

Please report any bugs or feature requests to bug-sub-fp at rt.cpan.org, or through the web interface at https://rt.cpan.org/NoAuth/ReportBug.html?Queue=Sub-Fp. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Sub::Fp

You can also look for information at:

ACKNOWLEDGEMENTS

LICENSE AND COPYRIGHT

MIT

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.