diff agda/laws.agda @ 97:f26a954cd068

Update Natural Transformation definitions
author Yasutaka Higa Tue, 20 Jan 2015 16:27:55 +0900 bcd4fe52a504 9c62373bd474
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```--- a/agda/laws.agda	Tue Jan 20 16:25:53 2015 +0900
+++ b/agda/laws.agda	Tue Jan 20 16:27:55 2015 +0900
@@ -4,33 +4,34 @@

module laws where

-record Functor {l : Level} (F : Set l -> Set l) : (Set (suc l)) where
+record Functor {l : Level} (F : {l' : Level} -> Set l' -> Set l') : Set (suc l) where
field
fmap : {A B : Set l} -> (A -> B) -> (F A) -> (F B)
field
preserve-id : {A : Set l} (x : F A) → fmap id x ≡ id x
covariant   : {A B C : Set l} (f : A -> B) -> (g : B -> C) -> (x : F A)
-> fmap (g ∙ f) x ≡ ((fmap g) ∙ (fmap f)) x
+
open Functor

+record NaturalTransformation {l : Level} (F G : {l' : Level} -> Set l' -> Set l')
+                                         {fmapF : {A B : Set l} -> (A -> B) -> (F A) -> (F B)}
+                                         {fmapG : {A B : Set l} -> (A -> B) -> (G A) -> (G B)}
+                                         (natural-transformation : {A : Set l}  -> F A -> G A)
+                             : Set (suc l) where
+  field
+    commute : {A B : Set l} -> (f : A -> B) -> (x : F A) ->
+              natural-transformation (fmapF f x) ≡  fmapG f (natural-transformation x)
+open NaturalTransformation

-record NaturalTransformation {l : Level} (F G : Set l -> Set l)
-                                            (functorF : Functor F)
-                                            (functorG : Functor G) : Set (suc l) where
-  field
-    natural-transformation : {A : Set l}  -> F A -> G A
-  field
-    commute : ∀ {A B} -> (f : A -> B) -> (x : F A) ->
-              natural-transformation (fmap functorF f x) ≡  fmap functorG f (natural-transformation x)
-open NaturalTransformation

-- simple Monad definition. without NaturalTransformation (mu, eta) and monad-law with f.
record Monad {l : Level} {A : Set l}
(M : {ll : Level} -> Set ll -> Set ll)
-                         (functorM : Functor M)
+                         (functorM : Functor {l} M)
: Set (suc l)  where
field -- category
mu  :  {A : Set l} -> M (M A) -> M A
@@ -43,4 +44,4 @@
left-unity-law  : (x : M A) -> (mu  ∙ (fmap functorM eta)) x ≡ id x
right-unity-law : (x : M A) -> id x ≡ (mu ∙ eta) x