fromValidator combinator for conversion from data.validator to lens

package.json

@@ -21,6 +21,7 @@
   "devDependencies": {
     "chai": "^1.9.1",
     "coffee-script": "^1.7.1",
+    "data.validation": "^1.2.0",
     "grunt": "^0.4.5",
     "grunt-coffeelint": "0.0.10",
     "grunt-contrib-clean": "^0.5.0",

src/agson/combinators.coffee

@@ -1,4 +1,4 @@
-{Just, Nothing, fromNullable} = require 'data.maybe'
+{Just, Nothing, fromNullable, fromValidation} = require 'data.maybe'
 
 lens = require('./Lens').of
 {identity} = require './lenses'
@@ -58,7 +58,21 @@ product = do ->
             abl.runM(result).modify -> mb
         result
 
+fromValidator = (validator) -> lens "validate", (ma) ->
+  get: ->
+    ma.chain (a) ->
+      fromValidation validator a
+
+  modify: (f) ->
+    ma.chain (a) ->
+      validb = fromValidation(validator a)
+      if validb.isJust
+        f validb
+      else
+        ma
+
 module.exports = {
   where
   product
+  fromValidator
 }

test/agson/CombinatorSpec.coffee

@@ -1,5 +1,8 @@
 {Just, Nothing} = require 'data.maybe'
+Validation = require 'data.validation'
+
 require('chai').should()
+
 lenses = require '../../src/agson/lenses'
 traversals = require '../../src/agson/traversals'
 combinators = require '../../src/agson/combinators'
@@ -115,7 +118,7 @@ describe 'agson.combinators', ->
 
     describe 'recursing down a cons list', ->
       {recurse} = traversals
-      
+
       List =
         Cons: (head, tail) -> {head, tail}
         Nil: {}
@@ -182,3 +185,28 @@ describe 'agson.combinators', ->
           .map((v) -> v + 1)
           .should.deep.equal Just [2, { foo: 3 }, [ 4, { bar: 5 } ] ]
 
+  describe 'fromValidator', ->
+    {fromValidator} = combinators
+    {list} = traversals
+
+    numberValidator = (input) ->
+      if typeof input is 'number'
+        Validation.Success input
+      else
+        Validation.Failure ['not a number']
+
+    numberList = list.then(fromValidator numberValidator)
+
+    describe 'get', ->
+      it 'gets items through validator', ->
+        numberList
+          .run([1, 2, 3, 'foo'])
+          .get()
+          .should.deep.equal Just [ 1, 2, 3 ]
+
+    describe 'modify', ->
+      it 'modifies items through validator', ->
+        numberList
+          .run([1, 2, 3, 'foo'])
+          .map((v) -> v + 1)
+          .should.deep.equal Just [2, 3, 4, 'foo']