The following primitive types have been identified.

All other types can be composed from them by using those and the operators.


BoolA value of type boolean can be either true or false
IntTODO: The classical integer type with 32-bit or 64-bit depending on the current system?
FloatA float with 64 bits?
StringA string of any unicode characters
PathPath referencing a location or a file. With no assumptions on the existence of that
NullThe value null

The Any type

The Any type is often used to explicitly allow arbitrary values. However, the Any type is complex and doesn't add much value to a type system. Instead, we should use type variables whenever possible.

Interestingly there are two different Any types:

e.g. If we look at CUE-lang (which is also inspired by nix)

CUE defines the values bottom, or error, (denoted |) that is an instance of all types and top, or any, (denoted _) of which all types are an instance.

  • TOP any all types are an instance of that. You can imagine it as the TOP-most set, that includes every type. But no value has that type.

  • Bottom any which is an instance of all types. This is kind of the imaginary value that has the any type. Still, doesn't contain any value. Which could also be denoted: Never or Empty Type it is a type that is the subtype of any type.

The following is a nice quote from the Typescript world

The any type is so dangerous because it exists outside of the type tree. It is both a top and bottom type. Everything can be assigned to it and it can be assigned to everything else. ...