Functional data structures for Python.

Usage

$ pip install pygow==0.5

Features

Maybe

A Maybe represents an optional value. It can be either Nothing, or Just(a) for some value a.

A Maybe instance includes the following methods:

• is_just(): Returns true if this is a Just, or false if it is a Nothing
• map(f): Applies the function f to the underlying value a, if any, and returns a new Maybe containing it
• flat_map(f): Applies the function f to the underlying value a, if any, and returns the resulting Maybe instance
• get_or_else(x): Returns the underlying value a, if any, otherwise returns the parameter x
• or_else(x): Returns this Maybe instance if it is a Just, otherwise returns the parameter x
• to_validation(e): Returns a Valid(a) if this is a Just(a), or Invalid([e]) if this is a Nothing

The maybe module includes the following functions:

• get_maybe_env(name): Returns a Maybe of the named environment variable
• non_empty_string(x): Returns a Just of the string x if it is non-empty, or Nothing otherwise
• parse_int(x): Returns a Just of the integer value of the string x, if it is parseable, or Nothing otherwise
• maybe(x): Constructs a Maybe instance around the parameter x, returning Just if x is not None, and Nothing otherwise

Validation

A Validation represents the result of a validation operation. It can be either Valid(a) for some value a, or Invalid(es) for some list of errors es.

A Validation instance includes the following methods:

• is_valid(): Returns true if this is a Valid, or false if it is an Invalid
• map(f): Applies the function f to the underlying value a, if any, and returns a new Validation containing it
• flat_map(f): Applies the function f to the underlying value a, if any, and returns the resulting Validation
• ap(v): Applies the underlying value a, which must be a function, to the value v, and returns the resulting Validation
• to_maybe(): Returns a Just(a) if this is a Valid(a), and a Nothing if this is an Invalid(es)

The validation module includes the following functions:

• get_required_env(name): Returns a Validation of the named environment variable
• lift_a(f): Returns a Valid of the unary function f
• lift_aN(n, f): Returns a Valid of a curried representation of the N-arity function f.

Examples

See the tests for complete examples.

Development

To release a new version of pygow:

1. Configure ~/.pypirc:

   [server-login]
   username: YOUR_PYPI_USERNAME
   password: YOUR_PYPI_PASSWORD
   
   [pypi]
   repository: https://pypi.python.org/pypi
   
   [pypitest]
   repository: https://testpypi.python.org/pypi
   

2. Update the version number in setup.py

3. Commit all changes

4. Add a version tag to git: git tag 0.1

5. Publish to PyPI: python setup.py sdist upload -r pypi