Jia Hau's syntax idea

.js

// This language is based on the idea of json-like objects
// This is a comment

// Tagged union
// Like OCaml, the tag is not associated with the type name, in this case `nat`
// Essentially, `nat` is just a alias for the tagged union
type Nat = {#zero} | {#succ, of: nat}

// Variable & object initialization
people = {name='John', hobby='type theory'}

// Object deconstruction
{x, y := a} = {x := '1', y := '2'} // Expose x and a to current closure

// Typing a variable
{j}: {j: Nat} = {j := {#zero}}

// Object deconstruction with type assertion and re-aliasing
{j: Nat = k} = {j := 'hi'} // Compiler will throw error

// Function declaration with pattern matching
add: Function {
  in: {value: Nat, by: Nat},
  out: Nat
} = {
  {value, by = {#zero}} -> value,
  {value, by = {#succ, of: x}} -> {#succ, of=add{value, by=x}}
 }

// Function application
answer = add {value={#zero}, by={#succ, of={#zero}}}
                         
// Currying and Uniform Calling Syntax (UCS)
// The following are equivalent
add{value:= x, by:= y}
add{value:= x, by:= _} {by:= y}
add{value:= _, by:= y} {value:= x}
x.add{by:= y}
y.add{value:= x}
                  
// Generic types
type List := {
  {of: type = a} = {#nil} | {#cons, current: a, next: a.list}
}

// Parametric polymorphism and type inference
length: Function {
  in: {of: List {of: infer _}},
  out: nat
} = {
  {#nil} -> {#zero},
  {#cons, current, next} -> {#succ, of={#zero}}.add{by: next.length}
}