Type.Env: add instance One Env

Author: Anton-Latukha

ChangeLog.md

@@ -15,6 +15,13 @@
     * added fun:
       * `evalContent`
       * `addMetaInfo`
+      
+  * `Nix.Types.Assumption`:
+    * added instances:
+      * `Assumption`: `{Semigroup,Monoid,One}`
+  * `Nix.Type.Env`:
+    * added instances:
+      * `Env`: `{Semigroup,Monoid,One}`
 
 
 ### [(diff)](https://github.com/haskell-nix/hnix/compare/0.13.0.1...0.13.1#files_bucket) 0.13.1 (2021-05-22)

src/Nix/Type/Env.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE TypeFamilies #-}
 module Nix.Type.Env
   ( Env(..)
   , empty
@@ -35,14 +36,18 @@ instance Semigroup Env where
 instance Monoid Env where
   mempty = empty
 
+instance One Env where
+  type OneItem Env = (Name, Scheme)
+  one = uncurry singleton
+
 empty :: Env
 empty = TypeEnv mempty
 
 extend :: Env -> (Name, [Scheme]) -> Env
 extend env (x, s) = env { types = Map.insert x s (types env) }
 
 remove :: Env -> Name -> Env
-remove (TypeEnv env) var = TypeEnv (Map.delete var env)
+remove (TypeEnv env) var = TypeEnv $ Map.delete var env
 
 extends :: Env -> [(Name, [Scheme])] -> Env
 extends env xs = env { types = Map.fromList xs `Map.union` types env }