Add two new functions to manipulate with lists

Add list.skip(count) and list.take(count) functions to collect only
a part of original list.

Change-Id: Ic730713f0baad64385e37b36e378615482c7a75d
Closes-bug: #1362892

doc/source/murano_pl/built-in_functions.rst

@@ -0,0 +1,35 @@
+..
+      Copyright 2014 2014 Mirantis, Inc.
+
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+
+==================
+Built-In functions
+==================
+
+Murano has built-in functions which allows to do basic operations
+with Murano PL objects.
+
+List operations
+====================
+
+**list.skip(count)**
+
+This function returns a sliced subset of initial list. It is equal
+to Python a[count:] function.
+
+**list.take(count)**
+
+Returns first "count" elements of a list. IT is equal to a[:count]
+operation in Python.

doc/source/murano_pl/index.rst

@@ -0,0 +1,26 @@
+..
+      Copyright 2014 Mirantis, Inc.
+
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+.. _murano_pl:
+
+=========================
+Murano PL Guide
+=========================
+
+.. toctree::
+   :maxdepth: 2
+
+   built-in_functions
+

murano/engine/system/yaql_functions.py

@@ -21,6 +21,7 @@ import string
 import time
 import types
 
+import itertools
 import jsonpatch
 import jsonpointer
 import yaql.context
@@ -206,7 +207,10 @@ def _int(value):
 
 
 def _pselect(collection, composer):
-    return helpers.parallel_select(collection(), composer)
+    if isinstance(collection, types.ListType):
+        return helpers.parallel_select(collection, composer)
+    else:
+        return helpers.parallel_select(collection(), composer)
 
 
 def _patch(obj, patch):
@@ -296,6 +300,18 @@ def _merge_with(self, other):
     return helpers.merge_dicts(self, other)
 
 
+@yaql.context.EvalArg('collection', types.ListType)
+@yaql.context.EvalArg('count', int)
+def _skip(collection, count):
+    return itertools.islice(collection, count, None)
+
+
+@yaql.context.EvalArg('collection', types.ListType)
+@yaql.context.EvalArg('count', int)
+def _take(collection, count):
+    return itertools.islice(collection, count)
+
+
 def register(context):
     context.register_function(
         lambda json, mappings: _transform_json(json(), mappings()), 'bind')
@@ -329,3 +345,5 @@ def register(context):
     context.register_function(_values, 'values')
     context.register_function(_flatten, 'flatten')
     context.register_function(_merge_with, 'mergeWith')
+    context.register_function(_skip, 'skip')
+    context.register_function(_take, 'take')

murano/tests/unit/dsl/meta/TestEngineFunctions.yaml

@@ -213,3 +213,32 @@ Methods:
       - $doc: {}
       - Return: $doc.patch($patches)
 
+  testTake:
+    Arguments:
+      - list:
+          Contract: [$.int()]
+      - count:
+          Contract: $.int()
+    Body:
+      - Return: $list.take($count)
+
+  testSkip:
+    Arguments:
+      - list:
+          Contract: [$.int()]
+      - count:
+          Contract: $.int()
+    Body:
+      - Return: $list.skip($count)
+
+  testSkipTake:
+    Arguments:
+      - list:
+          Contract: [$.int()]
+      - start:
+          Contract: $.int()
+      - count:
+          Contract: $.int()
+    Body:
+      - $l: $list.skip($start)
+      - Return: $l.take($count)

murano/tests/unit/dsl/test_engine_yaql_functions.py

@@ -197,3 +197,22 @@ class TestEngineYaqlFunctions(test_case.DslTestCase):
         self.assertEqual(
             {'foo': 'bar', 'baz': [42]},
             self._runner.testPatch())
+
+    def test_skip(self):
+        self.assertEqual(
+            [3, 4, 5, 6],
+            self._runner.testSkip([1, 2, 3, 4, 5, 6], 2)
+        )
+
+    def test_take(self):
+        self.assertEqual(
+            [1, 2, 3],
+            self._runner.testTake([1, 2, 3, 4, 5, 6], 3)
+        )
+
+    def test_skip_take(self):
+        self.assertEqual(
+            [3, 4, 5],
+            self._runner.testSkipTake([1, 2, 3, 4, 5, 6, 7, 8],
+                                      2, 3)
+        )