https://github.com/rawleyfowler/monad-result

Result monad for Raku
https://github.com/rawleyfowler/monad-result

functional-programming monad raku

Last synced: 3 months ago
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Result monad for Raku

• Host: GitHub
• URL: https://github.com/rawleyfowler/monad-result
• Owner: rawleyfowler
• License: artistic-2.0
• Created: 2022-12-31T16:08:14.000Z (about 2 years ago)
• Default Branch: main
• Last Pushed: 2024-01-06T19:58:21.000Z (about 1 year ago)
• Last Synced: 2024-10-10T20:41:30.753Z (3 months ago)
• Topics: functional-programming, monad, raku
• Language: Raku
• Homepage:
• Size: 23.4 KB
• Stars: 4
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Monad-Result

[![SparrowCI](https://ci.sparrowhub.io/project/gh-rawleyfowler-Monad-Result/badge?)](https://ci.sparrowhub.io)

An implementation of the result monad from OCaml. This allows the developer to completely avoid exceptions.

Note the result type is not generic, and cannot be statically typed. I think this makes it more flexible overall, 

compared to OCaml's result monad. (Gradual typing ftw)!

## How to use (default)

```raku

use Monad::Result;

sub my-error-causing-function($value --> Monad::Result) {

  return Monad::Result.error('Bad value!') if $value eq 'bad';

  Monad::Result.ok('Value was good!');

}

# Bind operator: >>=:

my-error-causing-function('bad') >>=: -> $value {

  say $value; # Is not called because this is not bindable (it is an error!)

  return Monad::Result.ok($value);

};

my-error-causing-function('abc') >>=: -> $value {

  say $value; # Is said because this is bindable, it is OK!

  return Monad::Result.ok($value);

};

# Map operator: >>=?

# Since this call results in OK, we can map it!

my $result = (my-error-causing-function('abc') >>=? -> $value {

  $value ~ ' HELLO WORLD';

}); # Results Ok('abc HELLO WORLD');

say $result.is-ok; # True

# NOTE UNWRAP IS DANGEROUS (In this case we know it's okay though!)

say $result.unwrap; # 'abc HELLO WORLD';

```

## How to use (subs)

Subs exist as a separate import, because they interfere with a lot of common packages.

```raku

use Monad::Result :subs;

sub my-error-causing-function($value --> Monad::Result) {

  return error('Bad value!') if $value eq 'bad';

  ok('Value was good!');

}

# Bind operator: >>=:

my-error-causing-function('bad') >>=: -> $value {

  say $value; # Is not called because this is not bindable (it is an error!)

  return ok($value);

};

my-error-causing-function('abc') >>=: -> $value {

  say $value; # Is said because this is bindable, it is OK!

  return ok($value);

};

# Map operator: >>=?

# Since this call results in OK, we can map it!

my $result = (my-error-causing-function('abc') >>=? -> $value {

  $value ~ ' HELLO WORLD';

}); # Results Ok('abc HELLO WORLD');

say $result.is-ok; # True

# NOTE UNWRAP IS DANGEROUS!

say $result.unwrap; # 'abc HELLO WORLD';

```

## How to install

```bash

zef install Monad-Result

```

## LICENSE

Monad::Result is provided under the Artistic-2.0 license.