This guide will show the basics of Pathex.

Create paths

Path-closure should be created with Pathex.path/2 or Pathex.sigil_P/2

For example:

iex> p = path :x / 0

And the same path, but using the sigil

iex> p = ~P":x/0"naive

Paths created with Pathex.path/2 can have atoms, strings, integers, variables and anything else what can be used in pattern-matching. This means that passing function calls straight into Pathex.path/2 is not allowed and will result in a compilation error

Note: You don't have to capture used variables

iex> x = 1
iex> path :some_atom / x  # Right
iex> path :some_atom / ^x # Wrong
  • Strings, tuples, maps, functions, lists are treated only as Map keys.
  • Atoms are treated as Map or Keyword keys.
  • Positive integers are treated as Map keys or List and Tuple indexes
  • Negative integers are treated as Map keys or first element in List's view or prepending element in List's update or force_set operations
  • Variables are treated as other types. For example, variables containing negative integers are treated as negative integer values

Use paths

iex> p = path :indexes / 0
iex> Pathex.view %{indexes: [1, 2, 3]}, p

There are plently ways to use created paths. Every macro with human-readable name (except path and sigil_P) is a macro for using pathex. In all such macros first argument is an input structure and the second argument is a path-closure itself

Note: Path-closure which are created inside path-using macro are optimised to have only one operation generated (instead of default three). You can read more about path-closures and operations here

As usual

  • Macro without ! always return {:ok, result} or :error
  • Macro with ! return result or raise Pathex.Error

Common data access functions


Compose paths

Path-closures can be composed together to create new path-closure, every path comosition macro is a binary operator. Some compositions are optimized to have generate one closure even if multiple closures are used.

You can concat paths with Pathex.~>/2 composition macro

iex> p1 = path :x
iex> p2 = path :y
iex> composed_path = p1 ~> p2
iex> 1 = Pathex.view(%{x: [y: 1]}, composed_path)

Think about paths composition just like paths concatenation in shell

For example

iex> first_user = path :users / 0          # users/0
iex> name = path :name                     # name
iex> first_user_name = first_user ~> name  # users/0/name

Prebuilt paths

Pathex provides some prebuilt path-closure to solve exotic problems. You can find them in Pathex.Lenses module. You can read more about them in lenses guide