https://github.com/scmorrison/perl6-fp-notes
Notes on functional programing techniques with Perl 6
https://github.com/scmorrison/perl6-fp-notes
functional-programming perl6
Last synced: 9 months ago
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Notes on functional programing techniques with Perl 6
- Host: GitHub
- URL: https://github.com/scmorrison/perl6-fp-notes
- Owner: scmorrison
- Created: 2017-04-29T09:01:33.000Z (almost 9 years ago)
- Default Branch: master
- Last Pushed: 2017-04-30T08:44:01.000Z (almost 9 years ago)
- Last Synced: 2025-04-10T01:18:58.414Z (12 months ago)
- Topics: functional-programming, perl6
- Size: 2.93 KB
- Stars: 0
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Notes on functional programming with Perl 6
### Table of Contents
* __[Prelude](#prelude)__
* __[Notes](#notes)__
* [Immutability](#immutability)
* __[Getting Involved](#getting-involved)__
* __[Copying](#copying)__
* [License](#license)
* [Attribution](#attribution)
## Prelude
[Perl 6] is a multi-paradigm programming language that offers several features that make writing in a functional style simple, most of the time. Perl 6 is not a _*pure*_ functional programming language and shouldn't be treated as such. This repository was created to document various FP solutions and approaches using Perl 6.
**Note**: This is not to be considered the **one_true_way_to_write_perl_6** in any paradigm.
## Notes
### Immutability
* See the following articles regarding Immutability in Perl 6:
* [Perl 6 Information Model]
* [Rosetta Code - Enforced immutability#Perl 6]
* The following built-in types are considered immutable:
| Type | Description |
|---------------|--------------------------------------------------------------|
|**Str** | Perl string (finite sequence of Unicode characters) |
|**Int** | Perl integer (allows Inf/NaN, arbitrary precision, etc.) |
|**Num** | Perl number (approximate Real, generally via floating point) |
|**Rat** | Perl rational (exact Real, limited denominator) |
|**FatRat** | Perl rational (unlimited precision in both parts) |
|**Complex** | Perl complex number |
|**Bool** | Perl boolean |
|**Exception** | Perl exception |
|**Block** | Executable objects that have lexical scopes |
|**Seq** | A list of values (can be generated lazily) |
|**Range** | A pair of Ordered endpoints |
|**Set** | Unordered collection of values that allows no duplicates |
|**Bag** | Unordered collection of values that allows duplicates |
|**Enum** | An immutable Pair |
|**Map** | A mapping of Enums with no duplicate keys |
|**Signature** | Function parameters (left-hand side of a binding) |
|**Capture** | Function call arguments (right-hand side of a binding) |
|**Blob** | An undifferentiated mass of ints, an immutable Buf |
|**Instant** | A point on the continuous atomic timeline |
|**Duration** | The difference between two Instants |
* Use the bind `:=` infix for scalars, which defaults to 'ro':
```perl6
my $name := "Camelia";
$name = "Elaine";
Cannot assign to an immutable value
in block at line 1
```
Keep in mind, you can still re-bind using `:=`:
```perl6
my $name := "Camelia";
$name := "Elaine";
Elaine
```
* Lists without containers are `ro` immutable, use Lists instead of Arrays (@) for listy things:
```perl6
my $list = (1, 2, 3);
push $list, 4;
Cannot call 'push' on an immutable 'List'
in block at line 1
```
> A list is immutable, which means you cannot change the number of elements in a list. But if one of the elements happens to be a scalar container, you can still assign to it. [[1]]
In this example `$list[0]` is a `rw` container, `$x`, with a value of `42`. This will allow replacing the value inside the `$x` scalar container:
```perl6
my $x = 42;
my $list = ($x, 1, 2);
$list[0] = 23;
say $x; # 23
```
Instead, bind the `Int` value to `$x` which which creates a `ro` container:
```perl6
my $x := 42;
my $list = ($x, 1, 2);
$list[0] = 23; # Error
Cannot modify an immutable Int
in block at line 1
```
This example tries replacing the value of `$list[1]`, which is an immutable `Int`:
```perl6
my $x = 42;
my $list = ($x, 1, 2);
$list[1] = 23; # Error
Cannot modify an immutable Int
in block at line 1
```
Use Array (@) in subroutine signatures for FP-style list processing of slurpy subparams. Lists will not work here. The new `@` Array is `ro` immutable within the scope of the subroutine:
```perl6
multi sub do-sum([$head, *@tail] ) { do-sum( $head, @tail ); };
multi sub do-sum($total, [$head, *@tail] ) { do-sum( $total + $head, @tail ); };
multi sub do-sum($total, [] ) { $total; };
my List $list = (1,2,3,4);
do-sum($list);
# Attempting to modify an subparameter Array inside its subrouting
sub edit-param(($head, *@tail)) {
@tail[2] = 30; # Error
return ($head, @tail).flat;
};
say edit-param((1,2,3,4));
Cannot modify an immutable Int
```
Use Map for associative Arrays / Hash like behavior:
```perl6
my Map $list = (name => "Camelia", email => "camelia@perl6.tld").Map
Map.new((:email("camelia\@perl6.tld"),:name("Camelia")))
say $list;
Camelia
# Try modifying $list
$list = "Steve";
Cannot modify an immutable Str
in block at line 1
# Try adding a new key-value pair
$list = "camelia@perl6.tld";
Cannot modify an immutable Mu
in block at line 1
```
## Getting Involved
When you submit a PR and it gets merged, you will be automatically added as a collaborator, but if you wouldn't like to be added, please mention it in your submission.
The larger Perl 6 community is very approachable and does a great job of answering questions and helping those new to Perl 6. If you're looking for other projects to contribute to please see the [Perl 6 Most Wanted Modules][Perl 6 Most Wanted].
## Copying
### License
This work is licensed under a
[Creative Commons Attribution 3.0 Unported License][license]
### Attribution
https://github.com/scmorrison/perl6-fp-notes/graphs/contributors
[FP Notes on Perl 6 (this repo)]: https://github.com/scmorrison/perl6-fp-notes
[Perl 6]: http://perl6.org
[Perl 6 Most Wanted]: https://github.com/perl6/perl6-most-wanted
[Perl 6 Information Model]: http://www.dlugosz.com/Perl6/web/info-model-1.html
[Rosetta Code - Enforced immutability#Perl 6]: https://rosettacode.org/wiki/Enforced_immutability#Perl_6
[1]: https://docs.perl6.org/language/containers.html#Scalar_containers_and_listy_things
[license]: http://creativecommons.org/licenses/by/3.0/deed.en_US
[Elixir Style Guide]: https://github.com/levionessa/elixir_style_guide