Wondering what’s next for npm?Check out our public roadmap! »

    pratica
    TypeScript icon, indicating that this package has built-in type declarations

    2.0.3 • Public • Published

    npm Pratica License PRs Welcome

    🥃 Pratica

    Functional Programming for Pragmatists

    Why is this for pragmatists you say?

    Pratica sacrifices some common FP guidelines in order to provide a simpler and more approachable API that can be used to accomplish your goals quickly - while maintaining data integrity and saftey, through algrebraic data types.

    For V1 docs - check out v1 docs readme

    Install

    With yarn

    yarn add pratica

    or if you prefer npm

    npm i pratica

    Documentation

    Table of Contents

    Changes from V1 to V2

    If you are migrating from Pratica V1 to V2. Here is a small list of changes made:

    • Maybe() utility was renamed to nullable()
    • .default(() => 'value') was renamed to .alt('value') and does not require a function to be passed in, just a value.

    That's it. Enjoy.

    Monads

    Maybe

    Use this when dealing with nullable and unreliable data that needs actions performed upon.

    Maybe is great for making sure you do not cause runtime errors by accessing data that is not there because of unexpected nulls or undefineds.

    Every Maybe can either be of type Just or Nothing. When the data is available, it is wrapped with Just, if the data is missing, it is Nothing. The examples below should clarify futher.

    Maybe.map

    Map is used for running a function on the data inside the Maybe. Map will only run the function if the Maybe type is Just. If it's Nothing, the map will short circuit and be skipped.

    import { nullable } from 'pratica'
     
    const person = { name: 'Jason', age: 4 }
     
    // Example with real data
    nullable(person)
      .map(p => p.age)
      .map(age => age + 5)
      .cata({
        Just: age => console.log(age), // 9
        Nothing: () => console.log(`This function won't run`)
      })
     
    // Example with null data
    nullable(null)
      .map(p => p.age) // Maybe type is Nothing, so this function is skipped
      .map(age => age + 5) // Maybe type is Nothing, so this function is skipped
      .cata({
        Just: age => console.log(age), // Maybe type is Nothing, so this function is not run
        Nothing: () => console.log('Could not get age from person') // This function runs because Maybe is Nothing
      })
    Maybe.chain

    Chain is used when you want to return another Maybe when already inside a Maybe.

    import { nullable } from 'pratica'
     
    const person = { name: 'Jason', age: 4 }
     
    nullable(person)
      .chain(p => nullable(p.height)) // p.height does not exist so nullable returns a Nothing type, any .map, .chain, or .ap after a Nothing will be short circuited
      .map(height => height * 2.2) // this func won't even run because height is Nothing, so `undefined * 2.2` will never execute, preventing problems.
      .cata({
        Just: height => console.log(height), // this function won't run because the height is Nothing
        Nothing: () => console.log('This person has no height')
      })
    Maybe.alt

    Alt is a clean way of making sure you always return a Just with some default data inside.

    import { nullable } from 'pratica'
     
    // Example with default data
    nullable(null)
      .map(p => p.age) // won't run
      .map(age => age + 5) // won't run
      .alt(99) // the data is null so 99 is the default
      .cata({
        Just: age => console.log(age), // 99
        Nothing: () => console.log(`This function won't run because .alt() always returns a Just`)
      })
    Maybe.ap

    Sometime's working with Maybe can be reptitive to always call .map whenever needing to a apply a function to the contents of the Maybe. Here is an example using .ap to simplify this.

    Goal of this example, to perform operations on data inside the Maybe, without unwrapping the data with .map or .chain

    import { Just, nullable } from 'pratica'
     
    // Need something like this
    // Just(6) + Just(7) = Just(13)
    Just(x => y => x + y)
      .ap(Just(6))
      .ap(Just(7))
      .cata({
        Just: result => console.log(result), // 13
        Nothing: () => console.log(`This function won't run`)
      })
     
    nullable(null) // no function to apply
      .ap(Just(6))
      .ap(Just(7))
      .cata({
        Just: () => console.log(`This function won't run`),
        Nothing: () => console.log(`This function runs`)
      })
    Maybe.inspect

    Inspect is used for seeing a string respresentation of the Maybe. It is used mostly for Node logging which will automatically call inspect() on objects that have it, but you can use it too for debugging if you like.

    import { nullable } from 'pratica'
     
    const { log } = console
     
    log(nullable(86).inspect()) // `Just(86)`
    log(nullable('HELLO').inspect()) // `Just('HELLO')`
    log(nullable(null).inspect()) // `Nothing`
    log(nullable(undefined).inspect()) // `Nothing`
    Maybe.cata

    Cata is used at the end of your chain of computations. It is used for getting the final data from the Maybe. You must pass an object to .cata with 2 properties, Just and Nothing (capitalization matters), and both those properties must be a function. Those functions will run based on if the the computations above it return a Just or Nothing data type.

    Cata stands for catamorphism and in simple terms means that it extracts a value from inside any container.

    import { Just, Nothing } from 'pratica'
     
    const isOver6Feet = person => person.height > 6
      ? Just(person.height)
      : Nothing
     
    isOver6Feet({ height: 4.5 })
      .map(h => h / 2.2)
      .cata({
        Just: h => console.log(h), // this function doesn't run
        Nothing: () => console.log(`person is not over 6 feet`)
      })
    Maybe.toResult

    toResult is used for easily converting Maybe's to Result's. Any Maybe that is a Just will be converted to an Ok with the same value inside, and any value that was Nothing will be converted to an Err with no value passed. The cata will have to include Ok and Err instead of Just and Nothing.

    import { Just, Nothing } from 'pratica'
     
    Just(8)
      .toResult()
      .cata({
        Ok: n => console.log(n), // 8
        Err: () => console.log(`No value`) // this function doesn't run
      })
     
    Nothing
      .toResult()
      .cata({
        Ok: n => console.log(n), // this function doesn't run
        Err: () => console.log(`No value`) // this runs
      })
    Maybe.isJust

    isJust returns a boolean representing the type of the Maybe. If the Maybe is a Just type then true is returned, if it's a Nothing, returns false.

    import { Just, Nothing } from 'pratica'
     
    const isOver6Feet = height => height > 6
      ? Just(height)
      : Nothing
     
    const { log } = console
     
    log(isOver6Feet(7).isJust()) // true
    log(isOver6Feet(4).isJust()) // false
    Maybe.isNothing

    isNothing returns a boolean representing the type of the Maybe. If the Maybe is a Just type then false is returned, if it's a Nothing, returns true.

    import { Just, Nothing } from 'pratica'
     
    const isOver6Feet = height => height > 6
      ? Just(height)
      : Nothing
     
    const { log } = console
     
    log(isOver6Feet(7).isNothing()) // false
    log(isOver6Feet(4).isNothing()) // true
    Maybe.value

    value returns the encapsulated value within the Maybe. If the Maybe is a Just type, then the arg is returned, otherwise, if it is a Nothing, then it returns undefined.

    import { Just, Nothing } from 'pratica'
     
    const isOver6Feet = height => height > 6
      ? Just(height)
      : Nothing
     
    const { log } = console
     
    log(isOver6Feet(7).value()) // 7
    log(isOver6Feet(4).value()) // undefined

    Result

    Use this when dealing with conditional logic. Often a replacment for if statements - or for simplifying complex logic trees. A Result can either be an Ok or an Err type.

    Result.map
    import { Ok, Err } from 'pratica'
     
    const person = { name: 'jason', age: 4 }
     
    Ok(person)
      .map(p => p.name)
      .cata({
        Ok: name => console.log(name), // 'jason'
        Err: msg => console.error(msg) // this func does not run
      })
    Result.chain
    import { Ok, Err } from 'pratica'
     
    const person = { name: 'Jason', age: 4 }
     
    const isPerson = p => p.name && p.age
      ? Ok(p)
      : Err('Not a person')
     
    const isOlderThan2 = p => p.age > 2
      ? Ok(p)
      : Err('Not older than 2')
     
    const isJason = p => p.name === 'jason'
      ? Ok(p)
      : Err('Not jason')
     
    Ok(person)
      .chain(isPerson)
      .chain(isOlderThan2)
      .chain(isJason)
      .cata({
        Ok: p => console.log('this person satisfies all the checks'),
        Err: msg => console.log(msg) // if any checks return an Err, then this function will be called. If isPerson returns Err, then isOlderThan2 and isJason functions won't even execute, and the err msg would be 'Not a person'
      })
    Result.mapErr

    You can also modify errors that may return from any result before getting the final result, by using .mapErr or .chainErr.

    import { Err } from 'pratica'
     
    Err('Message:')
      .mapErr(x => x + ' Syntax Error')
      .map(x => x + 7) // ignored because it's an error
      .cata({
        Ok: x => console.log(x), // function not ran
        Err: x => console.log(x) // 'Message: Syntax Error'
      })
    Result.chainErr
    import { Err } from 'pratica'
     
    Err('Message:')
      .chainErr(x => x + Err(' Syntax Error'))
      .map(x => x + 7) // ignored because it's an error
      .cata({
        Ok: x => console.log(x), // function not ran
        Err: x => console.log(x) // 'Message: Syntax Error'
      })
    Result.swap

    Use .swap() to convert an Err to an Ok, or an Ok to an Err.

    import { Ok } from 'pratica'
     
    Ok('hello')
      .swap()
      .cata({
        Ok: () => console.log(`doesn't run`),
        Err: x => expect(x).toBe('hello') // true
      })
    Result.bimap

    Use .bimap() for easily modifying an Ok or an Err. Shorthand for providing both .map and .mapErr

    import { Ok } from 'pratica'
     
    Ok('hello')
      .bimap(x => x + ' world', x => x + ' goodbye')
      .cata({
        Ok: x => expect(x).toBe('hello world'), // true
        Err: () => {}
      })
     
    Err('hello')
      .bimap(x => x + ' world', x => x + ' goodbye')
      .cata({
        Ok: () => {},
        Err: x => expect(x).toBe('hello goodbye') // true
      })
    Result.ap
    import { Ok } from 'pratica'
     
    // Need something like this
    // Ok(6) + Ok(7) = Ok(13)
    Ok(x => y => x + y)
      .ap(Ok(6))
      .ap(Ok(7))
      .cata({
        Ok: result => console.log(result), // 13
        Err: () => console.log(`This function won't run`)
      })
     
    Ok(null) // no function to apply
      .ap(Ok(6))
      .ap(Ok(7))
      .cata({
        Ok: () => console.log(`This function won't run`),
        Err: () => console.log(`This function runs`)
      })
    Result.inspect
    import { Ok, Err } from 'pratica'
     
    const { log } = console
     
    log(Ok(86).inspect()) // `Ok(86)`
    log(Ok('HELLO').inspect()) // `Ok('HELLO')`
    log(Err('Something happened').inspect()) // `Err('Something happened')`
    log(Err(404).inspect()) // `Err(404)`
    Result.cata
    import { Ok, Err } from 'pratica'
     
    const isOver6Feet = person => person.height > 6
      ? Ok(person.height)
      : Err('person is not over 6 feet')
     
    isOver6Feet({ height: 4.5 })
      .map(h => h / 2.2)
      .cata({
        Ok: h => console.log(h), // this function doesn't run
        Err: msg => console.log(msg) // `person is not over 6 feet`
      })
    Result.toMaybe

    toMaybe is used for easily converting Result's to Maybe's. Any Result that is an Ok will be converted to a Just with the same value inside, and any value that was Err will be converted to a Nothing with no value passed. The cata will have to include Just and Nothing instead of Ok and Err.

    import { Ok, Err } from 'pratica'
     
    Ok(8)
      .toMaybe()
      .cata({
        Just: n => console.log(n), // 8
        Nothing: () => console.log(`No value`) // this function doesn't run
      })
     
    Err(8)
      .toMaybe()
      .cata({
        Just: n => console.log(n), // this function doesn't run
        Nothing: () => console.log(`No value`) // this runs
      })
    Result.isOk
    import { Ok, Err } from 'pratica'
     
    const isOver6Feet = height => height > 6
      ? Ok(height)
      : Err('Shorty')
     
    const { log } = console
     
    log(isOver6Feet(7).isOk()) // true
    log(isOver6Feet(4).isOk()) // false
    Result.isErr
    import { Ok, Err } from 'pratica'
     
    const isOver6Feet = height => height > 6
      ? Ok(height)
      : Err('Shorty')
     
    const { log } = console
     
    log(isOver6Feet(7).isErr()) // false
    log(isOver6Feet(4).isErr()) // true

    Utilities

    parseDate

    Safely parse date strings. parseDate returns a Maybe monad.

    import { parseDate } from 'pratica'
     
    const goodDate = '2019-02-13T21:04:10.984Z'
    const badDate = '2019-02-13T21:04:1'
     
    parseDate(goodDate).cata({
      Just: date => expect(date.toISOString()).toBe(goodDate),
      Nothing: () => console.log('could not parse date string') // this function doesn't run
    })
     
    parseDate(badDate).cata({
      Just: () => console.log(`this function doesn't run`),
      Nothing: () => 'this function runs'
    })
     
    // it's a maybe, so you can use chain/default/ap
    parseDate(null)
      .default(() => new Date())
      .cata({
        Just: date => date.toISOString(), // this runs
        Nothing: () => `doesn't run because of the .default()`
      })

    encase

    Safely run functions that may throw an error or crash. encase returns a Maybe type (so Just or Nothing).

    import { encase } from 'pratica'
     
    const throwableFunc = () => JSON.parse('<>')
     
    // this func doesn't throw, so Just is called
    encase(() => 'hello').cata({
      Just: x => console.log(x), // hello
      Nothing: () => console.log('func threw error') // this func doesn't run
    })
     
    // this function throws an error so Nothing is called
    encase(throwableFunc).cata({
      Just: json => console.log(`doesn't run`),
      Nothing: () => console.error('func threw an error') // this runs
    })

    encaseRes

    Safely run functions that may throw an error or crash. encaseRes returns a Result type (so Ok or Err). Similar to encase but the Err returns the error message.

    import { encaseRes } from 'pratica'
     
    const throwableFunc = () => JSON.parse('<>')
     
    // this func doesn't throw, so Ok is called
    encaseRes(() => 'hello').cata({
      Ok: x => console.log(x), // hello
      Err: () => console.log('func threw error') // this func doesn't run
    })
     
    // this function throws an error so Err is called
    encaseRes(throwableFunc).cata({
      Ok: json => console.log(`doesn't run`),
      Err: msg => console.error(msg) // SyntaxError: Unexpected token < in JSON at position 0
    })

    justs

    Filter out any non-Just data type from an array

    import { justs } from 'pratica'
     
    const data = [1, true, Just('hello'), Nothing, Ok('hey'), Err('No good')]
     
    justs(data) // returns [Just('hello')]

    oks

    Filter out any non-Ok data type from an array

    import { oks } from 'pratica'
     
    const data = [1, true, Just('hello'), Nothing, Ok('hey'), Err('No good')]
     
    oks(data) // returns [Ok('hey')]

    get

    Safely retrieve a nested property in an object. Returns a Maybe.

    import { get } from 'pratica'
     
    const data = {
      name: 'jason',
      children: [
        {
          name: 'bob'
        },
        {
          name: 'blanche',
          children: [
            {
              name: 'lera'
            }
          ]
        }
      ]
    }
     
    get(['children', 1, 'children', 0, 'name'])(data).cata({
      Just: name => expect(name).toBe('lera'), // true
      Nothing: () => console.log('no name') // doesn't run
    })

    head

    Safely get the first item in an array. Returns a Maybe.

    import { head } from 'pratica'
     
    const data = [5,1,2]
     
    // example with data
    head(data)
      .cata({
        Just: x => expect(x).toBe(5), // true,
        Nothing: () => console.log('No head') // won't run
      })
     
    // example with empty data
    head([])
      .cata({
        Just: x => console.log(x), // doesn't run
        Nothing: () => console.log('No head') // runs 
      })

    last

    Safely get the last item in an array. Returns a Maybe.

    import { last } from 'pratica'
     
    const data = [5,1,2]
     
    // example with data
    last(data)
      .cata({
        Just: x => expect(x).toBe(2), // true,
        Nothing: () => console.log('No last') // won't run
      })
     
    // example with empty data
    last([])
      .cata({
        Just: x => console.log(x), // doesn't run
        Nothing: () => console.log('No last') // runs 
      })

    tail

    Safely get the tail of an array (Everything except the first element). Returns a Maybe.

    import { tail } from 'pratica'
     
    const data = [5,1,2]
     
    // example with data
    tail(data)
      .cata({
        Just: x => expect(x).toEqual([1,2]), // true,
        Nothing: () => console.log('No tail') // won't run
      })
     
    // example with empty data
    last([])
      .cata({
        Just: x => console.log(x), // doesn't run
        Nothing: () => console.log('No tail') // runs 
      })

    tryFind

    Safely try to retrieve an item from an array. Returns a Maybe.

    import { tryFind } from 'pratica'
     
    const users = [
      {name: 'jason', age: 6, id: '123abc'},
      {name: 'bob', age: 68, id: '456def'}
    ]
     
    tryFind(u => u.id === '123abc')(users)
      .cata({
        Just: user => expect(user).toEqual(users[0]), // true
        Nothing: () => 'Could not find user with id 123abc' // doesn't run
      })

    Install

    npm i pratica

    DownloadsWeekly Downloads

    312

    Version

    2.0.3

    License

    Apache-2.0

    Unpacked Size

    55.5 kB

    Total Files

    22

    Last publish

    Collaborators

    • avatar