Method & assignment cascades for Nim, inspired by Smalltalk & Dart.

cascade is a macro for Nim that implements method cascades, a feature originally from Smalltalk that's made its way into modern languages like Dart and Kotlin.

It allows you to avoid repeating an object's name for each method call or assignment. A common case is something like a button:

# before
var res = Button()
res.text = "ok"
res.width = 30
res.color = "#13a89e"
res.enable()

With cascade, you don't need to repeat yourself:

# after
let btn = cascade Button():
  text = "ok"
  width = 30
  color = "#13a89e"
  enable()

Also notice you can avoid declaring a var if you don't need to modify the target object after the fact — the object is mutable within the cascade block but becomes a let binding outside of that block.

Install using Nimble:

nimble install cascade

Then import and use:

import cascade

let x = cascade y:
  z = 10
  f()

• field assignment

  let foo = cascade Foo():
    bar = 100
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  foo.bar = 100

• nested field assignment

  let foo = cascade Foo():
    bar.baz.qux = "awesome"
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  foo.bar.baz.qux = "awesome"

• proc/template/method calls

  let foo = cascade Foo():
    fn("hello", "world")
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  foo.fn("hello", "world")

• nested calls on fields

  let foo = cascade Foo():
    bar.baz.seqOfStrings.add "more awesome"
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  foo.bar.baz.seqOfStrings.add "more awesome"

• if and when conditionals

  let foo = cascade Foo():
    if someCondition: bar.baz = 2
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  if someCondition: foo.bar.baz = 2

• cascades can be nested within each other

  let foo = cascade Foo():
    bar = cascade Bar():
      baz = cascade Baz():
        str = "we're down here now!"
  
  # ↑ equivalent ↓
  
  var foo = Foo()
  foo.bar = Bar()
  foo.bar.baz = Baz(str: "we're down here now!")

Is something missing? Check the open issues first or open a new one. Pull requests are appreciated!

To build cascade from source you'll need to have Nim installed, and should also have Nimble, Nim's package manager.

1. Clone the repo: git clone https://github.com/haltcase/cascade.git
2. Move into the newly cloned directory: cd cascade
3. Make your changes: cascade.nim, tests/tests.nim
4. Run tests: nimble test

You can check the issues for anything unresolved, search for a problem you're encountering, or open a new one. Pull requests for improvements are also welcome.

MIT © Bo Lingen / haltcase