https://github.com/samuelschlesinger/merge

Describe merging of data types
https://github.com/samuelschlesinger/merge

Last synced: 22 days ago
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Describe merging of data types

• Host: GitHub
• URL: https://github.com/samuelschlesinger/merge
• Owner: SamuelSchlesinger
• License: mit
• Created: 2021-09-16T08:57:33.000Z (over 3 years ago)
• Default Branch: master
• Last Pushed: 2021-09-19T00:54:58.000Z (over 3 years ago)
• Last Synced: 2024-10-27T19:10:53.646Z (2 months ago)
• Language: Haskell
• Size: 12.7 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# Merge

Often, one finds themselves having multiple sources of knowledge

for some piece of data, and having to merge these together. Perhaps

we have a type representing partial information about a digital friend.

```haskell

data Friend = Friend

  { name :: Maybe Text

  , email :: Maybe Text

  , age :: Max Int

  , pubKey :: PublicKey

  }

```

If we learn some information about a friend from someone, and some

from someone else, we'll want to merge that information to have a

more complete picture. That said, it might not succeed, as we may

have inconsistent information like two different names or different

public keys. We'll want a function of type:

```haskell

f :: Friend -> Friend -> Maybe Friend

```

That's the pattern that this library encapsulates!

```

mergeFriends :: Merge [String] Friend Friend

mergeFriends =

  User

    <$> optional name   .? ["name"]

    <*> optional email  .? ["email"]

    <*> combine age     .? ["age"]

    <*> required pubKey .? ["pubKey"]

f :: Friend -> Friend -> Validation [String] Friend

f x y = runMerge mergeFriends x y

```

We didn't get exactly what we thought we wanted, but this Validation

type is better: it is an Applicative which accumulates the errors for

every field.