Add Validation -> Maybe conversion method

README.md

@@ -56,6 +56,8 @@ A `Validation` instance includes the following methods:
   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:
 

pygow/validation.py

@@ -1,3 +1,5 @@
+import maybe
+
 class Valid:
     a = None
     def __init__(self, a):
@@ -20,6 +22,8 @@ def ap(self, v):
             return Valid(self.a(v.a))
         else:
             return v
+    def to_maybe(self):
+        return maybe.Just(self.a)
 
 class Invalid:
     es = None
@@ -43,6 +47,8 @@ def ap(self, v):
             return self
         else:
             return Invalid(self.es + v.es)
+    def to_maybe(self):
+        return maybe.Nothing()
 
 def get_required_env(name):
     from os import getenv

tests/test_validation.py

@@ -1,5 +1,5 @@
 from nose.tools import assert_true, assert_false, assert_equals
-from pygow import validation
+from pygow import validation, maybe
 
 def multBy(x):
     def k(y):
@@ -46,6 +46,10 @@ def test_get_required_env():
     assert_true(validation.get_required_env('HOME').is_valid())
     assert_false(validation.get_required_env('THIS_AINT_AN_ENV_VAR').is_valid())
 
+def test_to_maybe():
+  assert_equals(maybe.Just(42), validation.Valid(42).to_maybe())
+  assert_equals(maybe.Nothing(), validation.Invalid(['nope']).to_maybe())
+
 a_v = validation.Valid('a')
 a_i = validation.Invalid(['invalid: a'])
 def test_lift_a():