nickel/doc/manual/cookbook.md

Cookbook

For now, this is an unorganized, temporary document not to forget some pieces of the user manual that are not yet put in the right place.

Library (record of functions)

You should use type annotations for records of functions. Currently Nickel doesn't have a specific notion of a library or a module. You can just put functions inside a record. In accordance with the previous section, you should also use a type annotation on your record to make the type of the functions accessible to the outside. Otherwise, the record is typed as Dyn and will obliterate the types, making your library basically unusable inside typed code.

Example

DON'T

{
  foo :  Num -> Num = fun x => x + 1,
  bar : Num -> Num = foo,
}

BUT DO

{
  foo = fun x => x + 1,
  bar = foo,
} : {
  foo : Num -> Num,
  bar : Num -> Num,
}

Alternatively, you can repeat your types both at the function level and at the record level. It makes code more navigable and query-friendly, but at the expense of repetition and duplicated contract checks. It is also currently required for polymorphic functions because of the following bug. A better solution will probably be implemented in the future: type holes (TODO: MAY ACTUALLY BE AVAILABLE FOR RELEASE)

(NOT YET POSSIBLE)

{
  foo : Num -> Num = fun x => x + 1,
  bar : Num -> Num = foo,
} : _