F# for java programmers

With small code examples you will :
* Understand the syntax and philosophy differences between Java & F#
* Different defaults
* Less noise
* Algebraic type systems
* Discriminated unions
* Understand how types are executable documentations
* How it helps correctness by making illegal unrepresentable states

Let’s discover this really good language all together.

Transcript

1. @yot88
   F#
   FOR JAVA PROGRAMMERS
   F#
   JAVA
   

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2. @yot88
   WHAT IS F# ?
   λDifferences between Java and F#
   λ Concise syntax
   λ Type inference
   λ Different defaults
   λ Different philosophy
   λSpecial to F#
   λ Functional-first
   λ Algebraic type system
   λ Interactivity
   

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3. @yot88
   WHAT IS F# ?
   λFunctional language derived from OCaml
   λDeveloped by Microsoft Research
   λ Shipped with Visual Studio in 2010
   λOpen source
   λCross platform
   λFunctional language on .NET
   

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4. @yot88
   SYNTAX
   

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5. @yot88
   Immutable Java class
   public class Person {
   private final String name;
   private final Date birthday;
   public Person(String name, Date birthday) {
   this.name = name;
   this.birthday = birthday;
   }
   public String getName() {
   return name;
   }
   public Date getBirthday() {
   return birthday;
   }
   }
   

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6. @yot88
   Do we really need
   curly braces ?
   INDENTATION instead of curly braces
   public class Person {
   private final String name;
   private final Date birthday;
   public Person(String name, Date birthday) {
   this.name = name;
   this.birthday = birthday;
   }
   public String getName() {
   return name;
   }
   public Date getBirthday() {
   return birthday;
   }
   }
   

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7. @yot88
   Use = to start blocks
   public class Person =
   private final String name;
   private final Date birthday;
   public Person(String name, Date birthday) =
   this.name = name;
   this.birthday = birthday;
   public String getName() =
   return name;
   public Date getBirthday() =
   return birthday;
   INDENTATION instead of curly braces
   

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8. @yot88
   AUTOMATICALLY create BACKING FIELDS from
   constructor parameters
   public class Person =
   private final String name;
   private final Date birthday;
   public Person(String name, Date birthday) =
   this.name = name;
   this.birthday = birthday;
   public String getName() =
   return name;
   public Date getBirthday() =
   return birthday;
   A lot of duplication
   

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9. @yot88
   public class Person =
   public Person(String name, Date birthday) =
   public String getName() =
   return name;
   public Date getBirthday() =
   return birthday;
   Use constructor params directly
   AUTOMATICALLY create BACKING FIELDS from
   constructor parameters
   

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10. @yot88
    MERGE THE PRIMARY CONSTRUCTOR WITH THE
    CLASS DEFINITION
    public class Person(String name, Date birthday) =
    public String getName() =
    return name;
    public Date getBirthday() =
    return birthday;
    Merge constructor
    with the class definition
    

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11. @yot88
    LESS SYNTAX NOISE
    public class Person(String name, Date birthday) =
    public String getName() =
    return name;
    public Date getBirthday() =
    return birthday;
    Why do we need semi-colons ?
    

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12. @yot88
    LESS SYNTAX NOISE
    public class Person(String name, Date birthday) =
    public String getName() =
    return name
    public Date getBirthday() =
    return birthday
    No more semi-colons
    

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13. @yot88
    NO“RETURN”NEEDED
    public class Person(String name, Date birthday) =
    public String getName() =
    return name
    public Date getBirthday() =
    return birthday
    F# is an expression-oriented
    language
    

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14. @yot88
    The return is implicit for
    the last line in a block
    public class Person(String name, Date birthday) =
    public String getName() =
    name
    public Date getBirthday() =
    birthday
    NO“RETURN”NEEDED
    

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15. @yot88
    MEMBERS ARE PUBLIC BY DEFAULT
    Properties are immutable
    public class Person(String name, Date birthday) =
    public String getName() =
    name
    public Date getBirthday() =
    birthday
    

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16. @yot88
    NO GET IN F#
    class Person(String name, Date birthday) =
    String getName() =
    name
    Date getBirthday() =
    birthday
    class Person(String name, Date birthday) =
    String Name =
    name
    Date Birthday =
    birthday
    

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17. @yot88
    TYPE INFERENCE
    Why do we have to repeat the
    types?
    Can't the compiler figure it out for us?
    class Person(String name, Date birthday) =
    String Name =
    name
    Date Birthday =
    birthday
    

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18. @yot88
    Type inference
    Remove types
    Indicates they are class members
    class Person(String name, Date birthday) =
    Name =
    name
    Birthday =
    birthday class Person(String name, Date birthday) =
    member this.Name =
    name
    member this.Birthday =
    birthday
    

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19. @yot88
    Type inference
    class Person(String name, Date birthday) =
    member this.Name =
    name
    member this.Birthday =
    birthday
    member this.Age =
    var timeDiff = new Date().getTime() - birthday.getTime()
    var daysDiff = TimeUnit.DAYS.convert(timeDiff, TimeUnit.MILLISECONDS)
    daysDiff / 365
    Define method the same way
    

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20. @yot88
    TYPE ANNOTATION
    In F#, types come after name
    class Person(name: string, birthday: Date) =
    member this.Name =
    name
    member this.Birthday =
    birthday
    member this.Age =
    var timeDiff = new Date().getTime() - birthday.getTime()
    var daysDiff = TimeUnit.DAYS.convert(timeDiff, TimeUnit.MILLISECONDS)
    daysDiff / 365
    

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21. @yot88
    DIFFERENT KEYWORDS
    In java, we use class and var
    class Person(name: string, birthday: Date) =
    member this.Name =
    name
    member this.Birthday =
    birthday
    member this.Age =
    var timeDiff = new Date().getTime() - birthday.getTime()
    var daysDiff = TimeUnit.DAYS.convert(timeDiff, TimeUnit.MILLISECONDS)
    daysDiff / 365
    

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22. @yot88
    DIFFERENT KEYWORDS
    In F#, we use type and let
    type Person(name: string, birthday: Date) =
    member this.Name =
    name
    member this.Birthday =
    birthday
    member this.Age =
    let timeDiff = new Date().getTime() - birthday.getTime()
    let daysDiff = TimeUnit.DAYS.convert(timeDiff, TimeUnit.MILLISECONDS)
    daysDiff / 365
    

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23. @yot88
    FP SYNTAX : Separate data from the functions
    Define record types
    Define a function
    that acts on the type
    Functions have spaces
    between parameters
    // Inferred types of the function
    age : Person -> int
    

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24. FROM 21 TO 6 LINES OF CODE
    

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25. @yot88
    COMPOSITION
    Compose new functions by using >>
    

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26. @yot88
    PIPING
    Pipe functions with |>
    

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27. @yot88
    TYPE INFERENCE
    

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28. TYPE INFERENCE
    Inferred type of doSomething :
    val doSomething : f:(int -> string) -> x:int -> string
    x must be an int
    y must be a string
    f must be a ‘int -> string’ function
    type of f type of x return type
    

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29. @yot88
    LESS NOISE, MORE LOGIC
    // C# code
    public IEnumerable> GroupBy(
    IEnumerable source,
    Func keySelector
    )
    {
    ...
    }
    let groupBy source keySelector =
    …
    

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30. @yot88
    DIFFERENT DEFAULTS
    

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31. @yot88
    DIFFERENT DEFAULTS
    λImmutable by default
    λmutable is special case
    λNon-null types/classes by default
    λNullable is special case
    λStructural equality by default
    λreference equality is special case
    λEverything must be initialized
    

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32. @yot88
    IMMUTABILITY BY DEFAULT
    Error x is not mutable
    Use mutable keyword
    

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33. @yot88
    NOT NULLABLE BY DEFAULT
    Must be explicit on the type
    []
    

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34. @yot88
    STRUCTURAL EQUALITY
    No more getHashCode & equals to write
    

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35. @yot88
    ALGEBRAIC TYPE SYSTEMS
    

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36. @yot88
    TYPE != CLASS
    A type is a name for a set of things
    

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37. @yot88
    TYPE != CLASS
    

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38. @yot88
    F# TYPES CAN BE COMPOSED
    New types are built from smaller types using:
    AND OR
    Discriminated unions
    

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39. F# TYPES CAN BE COMPOSED
    Discriminated unions
    Each component type (called a union case) must be tagged with a
    label (called a case identifier or tag) so that they can be told apart (“discriminated”).
    The labels can be any identifier you like, but must start with an uppercase letter.
    

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40. @yot88
    REAL LIFE EXAMPLE
    λWe accept three forms of payment:
    λ Cash, Check, or Card.
    λFor Cash we don't need any extra information
    λFor Checks we need a check number
    λFor Cards we need a card type and card number
    

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41. REAL LIFE EXAMPLE
    We accept three forms of payment:
    Cash, Check, or Card.
    For Checks we need a check number
    For Cards we need a card type and card
    number
    OR type
    Primitive type
    AND type
    

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42. REAL LIFE EXAMPLE
    Types are executable
    documentation
    Discriminated Unions are a powerful tool for mapping
    intuitive types to a domain.
    Help code correctness by making illegal
    states unrepresentable
    

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43. REAL LIFE EXAMPLE
    Manipulate collections
    amount 57.000000
    amount 250.000000
    Ignore to throw away the
    result
    

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44. REAL LIFE EXAMPLE
    Pattern matching on inner fields
    https://github.com/swlaschin/DomainModelingMadeFunctional/tree/master/src/OrderTakingEvolved
    

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45. HOW SHOULD I ORGANIZE MY CODE IF I
    DON’T USE CLASSES?
    Use modules not classes
    There are three common patterns for mixing types and functions together
    Declare Types in the SAME MODULE as
    the functions.
    Declare Types SEPARATELY from the functions but in
    the SAME FILE.
    

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46. Type declared separately from the functions and in a different file
    Containing type definitions only.
    HOW SHOULD I ORGANIZE MY CODE IF I
    DON’T USE CLASSES?
    

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47. @yot88
    ALL THE SYNTAX QUICKLY
    

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48. @yot88
    F# SYNTAX IN 60 SECONDS
    

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49. @yot88
    F# SYNTAX IN 60 SECONDS
    

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50. @yot88
    F# SYNTAX IN 60 SECONDS
    

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51. @yot88
    F# SYNTAX IN 60 SECONDS
    

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52. @yot88
    Comes from Option
    F# SYNTAX IN 60 SECONDS
    

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53. @yot88
    F# SYNTAX IN 60 SECONDS
    

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54. @yot88
    F# SYNTAX IN 60 SECONDS
    

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55. @yot88
    INTEROP WITH .NET LIBRARIES
    

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56. @yot88
    INTEROP
    λ F# natively supports
    λ .NET classes
    λ Interfaces
    λ Structures
    λ The interop is very straightforward
    For example, you can write an interface in C# and have the
    implementation be done in F#.
    

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57. @yot88
    INTEROP
    Use named parameter to help inference
    

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58. @yot88
    GIVE ME THE POWER
    

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59. @yot88
    ECOSYSTEM
    

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60. @yot88
    FABLE
    https://fable.io/repl/
    

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61. @yot88
    STAY SAFE (Full stack F#)
    https://github.com/CompositionalIT/SAFE-Dojo/
    https://safe-stack.github.io/docs/
    

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62. @yot88
    F# INTERACTIVE
    

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63. @yot88
    WE CAN START RIGHT NOW
    λ Using F# for development and DevOps scripts
    λ Using F# for testing
    λ Using F# for database related tasks
    λ Using F# to explore and develop interactively
    λ Other interesting ways of using F#
    λ Use F# for parsing
    λ Use F# for diagramming and visualization
    λ Use F# for accessing web-based data stores
    λ Use F# for data science and machine learning
    -- NO PERMISSION NEEDED
    https://fsharpforfunandprofit.com/posts/low-risk-ways-to-use-fsharp-at-work/
    [] let ``When 2 is added to 2 expect 4``() =
    Assert.AreEqual(4, 2+2)
    TRUE FOR ANY OTHER FUNCTIONAL LANGUAGE
    

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64. @yot88
    TO GO FURTHER
    

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65. FP AND ARCHITECTURE
    https://increment.com/software-architecture/primer-on-functional-architecture/
    

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66. @yot88
    SCOTT WLASCHIN
    BIG BOSS OF THE GAME
    https://fsharpforfunandprofit.com/
    

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67. @yot88
    RESOURCES
    ƛ https://fsharpforfunandprofit.com/
    ƛ https://fsharp.org/
    ƛ How to start with F# : Low risk ways to use F# at work
    ƛ https://www.youtube.com/watch?v=PLFl95c-IiU
    ƛ https://fable.io/
    ƛ https://safe-stack.github.io/
    

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