MLStyle.jl

ML language pattern provider for Julia

Check out documents here:

Or you want some examples.

Install

pkg> add MLStyle

Why ADT and pattern matching

Clarity

Let's start from a simple case.

function switch_task(status :: Int)
    @match status begin
        1 => "finish your homework:)"
        2 => "reading"
        3 => "put down your mobilephone and get outside for a one-hour exercise."
        4 => "go to some website and watch some live."
        _ => "sleep"
    end
end

For there is no switch-case in Julia syntax, sometimes there might be enormous single cases to hard-code, if-else-end does hurt for its verbosity.

Another example is getting specific data from different schemas. Assume that you have many deserialized JSON data, and they're in 3 schemas. Each of them represents some information of a person.

struct D1
  name : String
  age  : Int
  sex  : Int
end

struct D2
  nickname : String
  lifetime : Int
  gender   : Int
end

struct D3
  sex   : Int
  lifetime : Int
end
data :: Vector{Union{D1, D2, D3}}

Now your boss told you to extract age and gender from those people. How would you do?

Yes it's so easy:

extracted = map data do record
  if isa(record, D1)
    (data.age, data.sex)
  else if isa(data, D2)
    (data.lifetime, data.gender)
  else
    (data.lifetime, data.sex)
  end
end

However, in real word, data from different places could have so many schemas and you code will just swell both your editor and time. Think that your friends told you in the morning to take part in their party when knock off, but you have a series of these stupid tasks to finish...

Let's try something else that might make you more pleasant.

extracted = map data do record
  @match record
    D1(_, age, gender) |
    D2(_, age, gender) |
    D3(gender, age) => (age, gender)
    _               => @error "unknown schema"
  end
end

What do you think about this? I admit that writing codes like the above may not guarantee your attending to the party, but something is different, I think.