Add Min and Max newtypes (#2011)

daml-foundations/daml-ghc/daml-stdlib-src/DA/Semigroup.daml

@@ -0,0 +1,27 @@
+-- Copyright (c) 2019 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
+-- SPDX-License-Identifier: Apache-2.0
+
+daml 1.2
+module DA.Semigroup where
+
+-- | Semigroup under `min`
+--
+-- ```
+-- > Min 23 <> Min 42
+-- Min 23
+-- ```
+newtype Min a = Min a deriving (Eq, Ord, Show)
+
+instance Ord a => Semigroup (Min a) where
+  Min a <> Min b = Min (min a b)
+
+-- | Semigroup under `max`
+--
+-- ```
+-- > Max 23 <> Max 42
+-- Max 42
+-- ```
+newtype Max a = Max a deriving (Eq, Ord, Show)
+
+instance Ord a => Semigroup (Max a) where
+  Max a <> Max b = Max (max a b)

daml-foundations/daml-ghc/daml-stdlib-src/LibraryModules.daml

@@ -41,6 +41,7 @@ import DA.Optional.Total
 import DA.Optional
 import DA.Random
 import DA.Record
+import DA.Semigroup
 import DA.Text
 import DA.TextMap
 import DA.Time

daml-foundations/daml-ghc/tests/SemigroupTest.daml

@@ -0,0 +1,11 @@
+-- Copyright (c) 2019, Digital Asset (Switzerland) GmbH and/or its affiliates.
+-- All rights reserved.
+
+daml 1.2
+module SemigroupTest where
+
+import DA.Semigroup
+
+test = scenario do
+  assert $ Min (23 : Int) <> Min 42 == Min 23
+  assert $ Max (23 : Int) <> Max 42 == Max 42

daml-foundations/daml-ghc/tests/Stdlib.daml

@@ -24,6 +24,7 @@ import DA.NonEmpty()
 import DA.Optional()
 import DA.Random()
 import DA.Record()
+import DA.Semigroup()
 import DA.Text()
 import DA.Time()
 import DA.Traversable()

unreleased.rst

@@ -42,3 +42,5 @@ HEAD — ongoing
 - [DAML Standard Library] Add ``Sum`` and ``Product`` newtypes that
   provide ``Monoid`` instances based on the ``Additive`` and ``Multiplicative``
   instances of the underlying type.
+- [DAML Standard Library] Add ``Min`` and ``Max`` newtypes that
+  provide ``Semigroup`` instances based ``min`` and ``max``.