add Monad trait (#119)

Co-authored-by: Paul Cadman <[email protected]>

Stdlib/Data/List.juvix

@@ -84,3 +84,9 @@ applicativeListI : Applicative List :=
       | [] _ := []
       | (f :: fs) l := map f l ++ ap fs l
   };
+
+instance
+monadListI : Monad List :=
+  mkMonad@{
+    bind := flip concatMap
+  };

Stdlib/Data/Maybe.juvix

@@ -7,6 +7,7 @@ import Stdlib.Trait.Ord open;
 import Stdlib.Trait.Show open;
 import Stdlib.Trait.Functor open;
 import Stdlib.Trait.Applicative open;
+import Stdlib.Trait.Monad open;
 
 import Stdlib.Data.Bool.Base open;
 import Stdlib.Data.String.Base open;
@@ -61,3 +62,11 @@ applicativeMaybeI : Applicative Maybe :=
       | (just f) (just x) := just (f x)
       | _ _ := nothing
   };
+
+instance
+monadMaybeI : Monad Maybe :=
+  mkMonad@{
+    bind {A B} : Maybe A -> (A -> Maybe B) -> Maybe B
+      | nothing _ := nothing
+      | (just a) f := f a
+  };

Stdlib/Data/Result.juvix

@@ -49,3 +49,11 @@ applicativeResultI {err} : Applicative (Result err) :=
       | (ok _) (error e) := error e
       | (error e) _ := error e
   };
+
+instance
+monadResultI {err} : Monad (Result err) :=
+  mkMonad@{
+    bind {A B} : Result err A -> (A -> Result err B) -> Result err B
+      | (error e) _ := error e
+      | (ok a) f := f a
+  };

Stdlib/Trait.juvix

@@ -5,6 +5,7 @@ import Stdlib.Trait.Show as Show open using {Show; module Show} public;
 import Stdlib.Trait.Ord as Ord open using {Ord; module Ord} public;
 import Stdlib.Trait.Functor open public;
 import Stdlib.Trait.Applicative open public;
+import Stdlib.Trait.Monad open public;
 import Stdlib.Trait.Foldable open public;
 import Stdlib.Trait.Partial open public;
 import Stdlib.Trait.Natural open public;

Stdlib/Trait/Monad.juvix

@@ -0,0 +1,20 @@
+module Stdlib.Trait.Monad;
+
+import Stdlib.Data.Fixity open;
+import Stdlib.Trait.Applicative open;
+
+trait
+type Monad (m : Type -> Type) :=
+  mkMonad {
+    {{applicative}} : Applicative m;
+    builtin monad-bind
+    bind : {A B : Type} -> m A -> (A -> m B) -> m B
+  };
+
+open Monad public;
+
+syntax operator >>= seq;
+>>= {A B} {f : Type -> Type} {{Monad f}} (x : f A) (g : A -> f B) : f B := bind x g;
+
+syntax operator >=> seq;
+>=> {A B C} {f : Type -> Type} {{Monad f}} (h : A -> f B) (g : B -> f C) (a : A) : f C := h a >>= g;

test/Package.juvix

@@ -6,5 +6,5 @@ package : Package :=
   defaultPackage@?{
     name := "stdlib-test";
     dependencies :=
-      [path "../"; github "anoma" "juvix-quickcheck" "104c749950480ed5dad42c7385a020ff31ca8875"]
+      [path "../"; github "anoma" "juvix-quickcheck" "b398d3cd58f0a7fb9be24d57fc5b3d82f31de555"]
   };

test/juvix.lock.yaml

@@ -2,17 +2,17 @@
 # Do not edit this file manually.
 
 version: 2
-checksum: 74c7b4f7ff78859f15da9fa14ede6df5397c698d1efdcd5cc0f435d5cbb59e9d
+checksum: d7a0456ff0284c1898071b9775fbcf63ba5d9d7257e9583b9573581c16f0ec89
 dependencies:
 - path: ../
   dependencies: []
 - git:
     name: anoma_juvix-quickcheck
-    ref: 104c749950480ed5dad42c7385a020ff31ca8875
+    ref: b398d3cd58f0a7fb9be24d57fc5b3d82f31de555
     url: https://github.com/anoma/juvix-quickcheck
   dependencies:
   - git:
       name: anoma_juvix-stdlib
-      ref: 0ca2d5181e7c98eceace5c12bfd0a8cfb3d4d132
+      ref: af72f25057217619a03b7a5114000d02d0abed31
       url: https://github.com/anoma/juvix-stdlib
     dependencies: []