Small Type-Inferred Functional Language

Simple ML-inspired purely functional language with Hindley Milner type inferrence.

Language features

Functions
- Functions may only take one argument.
- fn x => y
- Top-level functions are anonymous functions bound to a name.
  - f = fn x => ...;
- Implicit generalized bindings
Function invocation
- f x
- Currying!
  - f x y = (f x) y
if-then-else expressions
- if cond then ifTrue else ifFalse
let bindings
- let x = y in z
Tuples
- (a, b, c)
Lists
- [a, b, c]
Undefined
- ?
- Throws an error at runtime.
- Only natural expression with bottom type as result.
Types
- 32-bit integers
- Booleans
- Functions (t1 -> t2)
- Tuples ((t1, t2, t3))
- Lists ([t])
- Type variables ('t)
- Unit (())
- Bottom (_)
  - Unifies with everything.
  - Expressions may not manually be typed with _.
  - May only be inferred from usage of ?.
Type annotations
- x: T
Type inferrence
- f = fn x => x; => f: 'a -> 'a
- f = fn isZero => if isZero 1 then 2 else 3; => f: (Int -> Bool) -> Int