Description of the data types handled by Drizzle


Below is a list of all the different built in datatypes that are in my thoughts for Drizzle.
Some of them I am currently unsure about, but for the most part these types should be pretty set in stone.


  • any is a special type that is used for type hinting collection type variables where the types of all the possible items in the collection is unknown.
  • list[any] allows a list of any type objects (list also works).
  • tuple[any] allows a tuple of any type objects (tuple also works).
  • dict[str, any] is a dictionary with string keys and any type values.
  • dict[any, any] allows both keys and values to be any hashable type (dict also works).
  • set[any] is a set of any hashable type
  • Please note that any only works for collection types. For now, I don't think like you should be allowed to declare an any type variable.


  • null is a special variable that represents nothing.
  • In cases where a variable can only be null, the variable can be typed with the none type
  • If a variable can be null then the type must be suffixed with a ? character, indicating that the variable is nullable.
    • let a: list[int] = null # ERROR
    • let b: list[int]? = null # OK
  • Return types can also be nullable.
    • def f() -> str = return null # ERROR
    • def f() -> str? = return null # OK
  • See the section on Nullable Types for more information

Nullable Types

  • If a type declaration has a ? suffix, then the type is considered nullable and can have null assigned to it.
  • If a user tries to use a nullable type without checking for null values the interpreter will warn them.
  • Nullables can be converted into their normal types by appending the ! character to the variable name.
    • let s: str? = 'abc' # s is of type str?
    • s = s! # now s is of type str
  • If the ! is used when the value of a nullable is null, an error will be thrown
  • You can check the value of a nullable by instead appending the ? character.
    • This will return a boolean stating whether the value of the variable is null or not
let s: str? = null
# Here, s is of type `str?`
if s? {
# Here we know s is not null, so s becomes the `str` type
else {
# Here we know s is null, so s becomes the `none` type
let t: str? = 'abc'
# Type of t is `str?`
t = t!
# Type of t is now `str`


  • int.
    • 64 bit integer.
  • float.
    • 64 bit floating point number.
  • oct
    • Octal number
  • hex
    • Hexadecimal number
  • num is a super type for all numeric types that can be used for param and return types in functions that can handle int and float types.
  • Like Ruby / Crystal, the numeric types in Drizzle will have methods (x: float =
  • Currently, I think we can just have a single int and float type for 64-bit integers and 64-bit floats for now.


  • 'Hello, World'.
  • String templating follows Ruby / Crystal style ('We just converted #{x} into a float').
  • For typing, str is used.


  • true, false.
  • For typing, bool is used.


  • a: list[int]: [1, 2, 3]
  • b: list: [1, 'abc', 3.1415]
  • Lists are mutable, like in Python
    • b[0] = 2 # => OK


  • c: tuple[int] = (1, 2, 3)
  • d: tuple = (1, 'abc', 3.1415)
  • Tuples are immutable
    • d[0] = 2 # => ERROR
  • A nice thing that having specified typing gives us is the possibility to do let x: tuple[int] = (1) and not have to add the extra , to denote a one-item tuple


  • map: dict[str, str] = {'a': 'b', 'b': 'a'}
  • map2: dict[str, any] = {'a': 'b', 'b': 2}
  • map3: dict = {0: 'a', 'b': 1}


  • s1: set[int] = {1, 2, 3}
  • s2: set = {1, 'b', 0xa}
A big plus Drizzle has over Python in this regard is that, due to Drizzle's type declarations, the {} literal can be used to define empty sets and empty dicts with no hassle*!
* A small bit of hassle might arise when using the literal in a conditional (if s == {}) but hopefully the parser will be able to handle it.


Following a similar style to Crystal, ranges are defined in two ways;
  • 0..5
    • Contains the numbers from 0 to 5 inclusive (0, 1, 2, 3, 4, 5)
  • 0...5
    • Contains the numbers from 0 to 5 exclusive (0, 1, 2, 3, 4)
As a metaphor to remember this, you can imagine that adding the third dot pushes the 5 out of the range.

Union Types

When something can be one of a select few types, e.g values in a dict, then they can by typed using union types.
Union types are simply a list of types separated by the | character.
For example, dict[str, str | int] is the type for a dictionary with string keys and either string or integer values.


As Drizzle supports higher order functions, meaning that functions can be passed as parameters, then these functions need to have a type hinting syntax.
The syntax is as simple as possible, simply the types in the argument tuple, the return type operator and the return type, all contained in parentheses.
For example, ((num, num) -> num) is the type for functions that take in two num type parameters and return a num type parameter.

Type Aliasing

To conserve time and energy, type aliases can be set up for cases where you have a large type definition that is used in multiple places.
Let's take the following value as an example;
[1, 'abc', {'a', 1}],
{'a': 1, 'b': ['a', 1, {'a': 'b'}]},
The type declaration for this monstrosity lovely value should look something like list[list[int | str | set[str | int]] | dict[str, int | list[str | int | dict[str, str]]]].
Imagine if you were using this type of data as a parameter and return type for many different functions. Sure you could copy and paste, but what if you had to allow integer keys in the dict of the list of the dict.. You get the picture.
Drizzle allows you to create a type alias without much effort, that you can use anywhere in the code. Let's take a look at the two ways we can create a variable to house this value;
# Not so good
let v: list[list[int | str | set[str | int]] | dict[str, int | list[str | int | dict[str, str]]]] = get_data()
def get_data() -> list[list[int | str | set[str | int]] | dict[str, int | list[str | int | dict[str, str]]]] {
return [
[1, 'abc', {'a', 1}],
{'a': 1, 'b': ['a', 1, {'a': 'b'}]},
# Much better
const monstrosity: type = list[list[int | str | set[str | int]] | dict[str, int | list[str | int | dict[str, str]]]]
let v: monstrosity = get_data()
def get_data() -> monstrosity {
return [
[1, 'abc', {'a', 1}],
{'a': 1, 'b': ['a', 1, {'a': 'b'}]},
There's nothing stopping you from writing your code in the first style, but it's probably far more preferential to use type aliasing in a situation like this. Hopefully, however, a type like this doesn't show up in your code all that often...