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IHaskell notebook on Isos in Optics Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
2020-01-12 06:44:06 +01:00
{
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{
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"import Control.Lens\n",
"import Data.Text\n",
"import qualified Data.Text as T\n",
"import qualified Control.Lens as L\n",
"\n",
"to :: String -> T.Text\n",
"to = T.pack\n",
"\n",
"from :: T.Text -> String\n",
"from = T.unpack"
]
},
{
"cell_type": "code",
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"source": [
"-- Transformations are completely reversible\n",
"\n",
"pack . unpack = id\n",
"unpack . pack = id"
]
},
{
"cell_type": "code",
"execution_count": 39,
"metadata": {},
"outputs": [],
"source": [
"-- Generally for all isomorphisms\n",
"\n",
"to . from = id\n",
"from . to = id"
]
},
{
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"execution_count": 41,
"metadata": {
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"</style><span class='get-type'>iso :: forall (p :: * -> * -> *) (f :: * -> *) s a b t. (Profunctor p, Functor f) => (s -> a) -> (b -> t) -> p a (f b) -> p s (f t)</span>"
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"-- iso :: (s -> a) -> (b -> t) -> Iso s t a b\n",
"-- Iso' s a where s ~ a and b ~ t\n",
"-- ~ means the types are equal\n",
"\n",
":t iso"
]
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"\"Ay, Caramba!\""
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"packed :: Iso' String T.Text\n",
"packed = iso to' from'\n",
" where \n",
" to' :: String -> T.Text\n",
" to' = T.pack\n",
" from' :: T.Text -> String\n",
" from' = T.unpack\n",
" \n",
"let x = (\"Ay, Caramba!\" :: String) ^. packed\n",
"x\n",
":t x\n",
"\n",
"-- # is review. Reviewing an iso returns it's inverse\n",
"-- We typically don't review iso's however, they have a different way of running things backwards\n",
"-- OverloadedStrings extension is required here else the next line will error out\n",
"\n",
":t (#)\n",
"let y = packed # (\"Sufferin' Succotash\" :: T.Text)\n",
"y\n",
":t y\n",
"\n",
":t L.from\n",
"\n",
"-- from :: Iso s t a b -> Iso b a t s\n",
"-- Simple form\n",
"-- from :: Iso' s a -> Iso' a s\n",
"\n",
"-- (#) :: forall t b. AReview t b -> (b -> t)\n",
"-- review returns a function and thus can be composed in an optics path\n",
"-- from returns a whole new Iso\n",
"\n",
"-- We can use from to flip existing Isos\n",
"\n",
"let x = (\"Good grief\" :: String) ^. packed\n",
"x\n",
":t x\n",
"\n",
"let y = (\"Good grief\" :: T.Text) ^. L.from packed\n",
"y\n",
":t y\n",
"\n",
"-- unpacked :: Iso' T.Text String\n",
"-- unpacked = from packed"
]
},
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"source": [
"## Modification under an Isomorphism\n",
"\n",
"* What does it mean to modify something through an Iso?\n",
"* Convert the data through the Iso, run the modification and then convert it back"
]
},
{
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"margin-left: 0.4em;\n",
"}\n",
".hoogle-package {\n",
"font-weight: bold;\n",
"font-style: italic;\n",
"}\n",
".hoogle-module {\n",
"font-weight: bold;\n",
"}\n",
".hoogle-class {\n",
"font-weight: bold;\n",
"}\n",
".get-type {\n",
"color: green;\n",
"font-weight: bold;\n",
"font-family: monospace;\n",
"display: block;\n",
"white-space: pre-wrap;\n",
"}\n",
".show-type {\n",
"color: green;\n",
"font-weight: bold;\n",
"font-family: monospace;\n",
"margin-left: 1em;\n",
"}\n",
".mono {\n",
"font-family: monospace;\n",
"display: block;\n",
"}\n",
".err-msg {\n",
"color: red;\n",
"font-style: italic;\n",
"font-family: monospace;\n",
"white-space: pre;\n",
"display: block;\n",
"}\n",
"#unshowable {\n",
"color: red;\n",
"font-weight: bold;\n",
"}\n",
".err-msg.in.collapse {\n",
"padding-top: 0.7em;\n",
"}\n",
".highlight-code {\n",
"white-space: pre;\n",
"font-family: monospace;\n",
"}\n",
".suggestion-warning { \n",
"font-weight: bold;\n",
"color: rgb(200, 130, 0);\n",
"}\n",
".suggestion-error { \n",
"font-weight: bold;\n",
"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>str2 :: String</span>"
],
"text/plain": [
"str2 :: String"
]
},
"metadata": {},
"output_type": "display_data"
}
],
"source": [
"let str = \"Idol on a pedestal\" :: String\n",
"str & packed %~ T.replace \"Idol\" \"Sand\"\n",
"\n",
"-- over ~ %~\n",
"let str2 = over packed (T.replace \"Idol\" \"Sand\") str\n",
"str2\n",
":t str2"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Isos are composable with other optics"
]
},
{
"cell_type": "code",
"execution_count": 60,
"metadata": {},
"outputs": [],
"source": [
"{-# LANGUAGE OverloadedStrings #-}\n",
"\n",
"import Data.Char as C\n",
"import Control.Lens as L\n",
"import Data.Text.Lens as TL\n",
"\n",
"let txt = \"Lorem Ipsum\" :: T.Text\n",
"\n",
"--txt & (from packed) . (traversed %~ C.toUpper)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Varieties of Isomorphisms"
]
},
{
"cell_type": "code",
"execution_count": 77,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"[1,2,3]"
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
"text/plain": [
"[1,2]"
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
"text/plain": [
"[3]"
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
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".hoogle-code {\n",
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"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>swapped :: forall (p1 :: * -> * -> *) (p2 :: * -> * -> *) (f :: * -> *) b a d c. (Swapped p1, Profunctor p2, Functor f) => p2 (p1 b a) (f (p1 d c)) -> p2 (p1 a b) (f (p1 c d))</span>"
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"swapped :: forall (p1 :: * -> * -> *) (p2 :: * -> * -> *) (f :: * -> *) b a d c. (Swapped p1, Profunctor p2, Functor f) => p2 (p1 b a) (f (p1 d c)) -> p2 (p1 a b) (f (p1 c d))"
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"data": {
"text/plain": [
"(\"Pride\",\"Fall\")"
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
"text/plain": [
"Left \"Field\""
]
},
"metadata": {},
"output_type": "display_data"
}
],
"source": [
"{-# LANGUAGE RankNTypes #-}\n",
"\n",
"import Data.List as List\n",
"\n",
"-- involuted :: (a -> a) -> Iso' a a\n",
"-- involuted f = iso f f\n",
"\n",
"-- reversed :: Iso' [a] [a]\n",
"-- reversed = involuted List.reverse\n",
"\n",
"List.reverse . List.reverse $ [1, 2, 3]\n",
"\n",
"[1, 2, 3] & reversed %~ List.drop 1\n",
"\n",
"[1, 2, 3] & reversed %~ List.take 1\n",
"\n",
"-- [1, 2, 3, 4] ^.. reversed . takingWhile (> 2) traversed\n",
"\n",
"-- swapped :: Iso' (a, b) (b a)\n",
":t swapped\n",
"\n",
"(\"Fall\", \"Pride\") ^. swapped\n",
"\n",
"-- swapped :: (Bifunctor p, Swapped p) => Iso (p a b) (p c d) (p b a) (p d c)\n",
"\n",
"Right \"Field\" ^. swapped"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Some more examples"
]
},
{
"cell_type": "code",
"execution_count": 82,
"metadata": {},
"outputs": [
{
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"color: red;\n",
"}\n",
".suggestion-name {\n",
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"}\n",
"</style><span class='get-type'>flipped :: forall (p :: * -> * -> *) (f :: * -> *) b a c b' a' c'. (Profunctor p, Functor f) => p (b -> a -> c) (f (b' -> a' -> c')) -> p (a -> b -> c) (f (a' -> b' -> c'))</span>"
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"data": {
"text/plain": [
"\"BA\""
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
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"}\n",
".hoogle-code {\n",
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".hoogle-text {\n",
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".mono {\n",
"font-family: monospace;\n",
"display: block;\n",
"}\n",
".err-msg {\n",
"color: red;\n",
"font-style: italic;\n",
"font-family: monospace;\n",
"white-space: pre;\n",
"display: block;\n",
"}\n",
"#unshowable {\n",
"color: red;\n",
"font-weight: bold;\n",
"}\n",
".err-msg.in.collapse {\n",
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".highlight-code {\n",
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"font-weight: bold;\n",
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".suggestion-error { \n",
"font-weight: bold;\n",
"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>curried :: forall (p :: * -> * -> *) (f1 :: * -> *) a b c d e f2. (Profunctor p, Functor f1) => p (a -> b -> c) (f1 (d -> e -> f2)) -> p ((a, b) -> c) (f1 ((d, e) -> f2))</span>"
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"display: block;\n",
"padding-bottom: 1.3em;\n",
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"}\n",
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"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>uncurried :: forall (p :: * -> * -> *) (f1 :: * -> *) a b c d e f2. (Profunctor p, Functor f1) => p ((a, b) -> c) (f1 ((d, e) -> f2)) -> p (a -> b -> c) (f1 (d -> e -> f2))</span>"
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"3"
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},
"metadata": {},
"output_type": "display_data"
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{
"data": {
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"-10"
]
},
"metadata": {},
"output_type": "display_data"
},
{
"data": {
"text/plain": [
"20"
]
},
"metadata": {},
"output_type": "display_data"
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"data": {
"text/plain": [
"150"
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"metadata": {},
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"source": [
"-- flipped :: Iso' (a -> b -> c) (b -> a -> c)\n",
"\n",
":t flipped\n",
"\n",
"let (++?) = (++) ^. flipped\n",
"\"A\" ++? \"B\"\n",
"\n",
"-- curried :: Iso' ((a, b) -> c) (a -> b -> c)\n",
"-- uncurried :: Iso' (a -> b -> c) ((a, b) -> c)\n",
"\n",
":t curried\n",
":t uncurried\n",
"\n",
"let addTuple = (+) ^. uncurried\n",
"addTuple (1, 2)\n",
"\n",
"import Numeric.Lens\n",
"\n",
"10 ^. negated\n",
"\n",
"over negated (+10) 30\n",
"\n",
"100 ^. adding 50"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Composing Isos"
]
},
{
"cell_type": "code",
"execution_count": 105,
"metadata": {},
"outputs": [
{
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"color: green;\n",
"font-weight: bold;\n",
"font-family: monospace;\n",
"margin-left: 1em;\n",
"}\n",
".mono {\n",
"font-family: monospace;\n",
"display: block;\n",
"}\n",
".err-msg {\n",
"color: red;\n",
"font-style: italic;\n",
"font-family: monospace;\n",
"white-space: pre;\n",
"display: block;\n",
"}\n",
"#unshowable {\n",
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"font-weight: bold;\n",
"}\n",
".err-msg.in.collapse {\n",
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"}\n",
".highlight-code {\n",
"white-space: pre;\n",
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"}\n",
".suggestion-warning { \n",
"font-weight: bold;\n",
"color: rgb(200, 130, 0);\n",
"}\n",
".suggestion-error { \n",
"font-weight: bold;\n",
"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>unpacked :: forall t (p :: * -> * -> *) (f :: * -> *). (IsText t, Profunctor p, Functor f) => p String (f String) -> p t (f t)</span>"
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"ename": "",
"evalue": "",
"output_type": "error",
"traceback": [
"<interactive>:1:43: error:\n • Couldn't match type ‘Char’ with ‘Bool’\n Expected type: Char -> Bool\n Actual type: Bool -> Bool\n • In the first argument of ‘T.takeWhile’, namely ‘(not . isSpace)’\n In the second argument of ‘(%~)’, namely ‘T.takeWhile (not . isSpace)’\n In the second argument of ‘(&)’, namely ‘unpacked . reversed %~ T.takeWhile (not . isSpace)’"
]
}
],
"source": [
"let txt = \"Winter is coming\" :: T.Text\n",
"\n",
":t unpacked \n",
"\n",
"-- txt ^. unpacked . reversed\n",
"\n",
"-- txt & unpacked . reversed %~ T.takeWhile (not . isSpace)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Projecting Isos"
]
},
{
"cell_type": "code",
"execution_count": 106,
"metadata": {},
"outputs": [
{
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"}\n",
".err-msg {\n",
"color: red;\n",
"font-style: italic;\n",
"font-family: monospace;\n",
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"display: block;\n",
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"#unshowable {\n",
"color: red;\n",
"font-weight: bold;\n",
"}\n",
".err-msg.in.collapse {\n",
"padding-top: 0.7em;\n",
"}\n",
".highlight-code {\n",
"white-space: pre;\n",
"font-family: monospace;\n",
"}\n",
".suggestion-warning { \n",
"font-weight: bold;\n",
"color: rgb(200, 130, 0);\n",
"}\n",
".suggestion-error { \n",
"font-weight: bold;\n",
"color: red;\n",
"}\n",
".suggestion-name {\n",
"font-weight: bold;\n",
"}\n",
"</style><span class='get-type'>mapping :: forall (p :: * -> * -> *) (f1 :: * -> *) (g :: * -> *) (f2 :: * -> *) s t a b. (Profunctor p, Functor f1, Functor g, Functor f2) => AnIso s t a b -> p (f1 a) (f2 (g b)) -> p (f1 s) (f2 (g t))</span>"
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"</style><span class='get-type'>contramapping :: forall (f1 :: * -> *) (p :: * -> * -> *) (f2 :: * -> *) s t a b. (Contravariant f1, Profunctor p, Functor f2) => AnIso s t a b -> p (f1 s) (f2 (f1 t)) -> p (f1 a) (f2 (f1 b))</span>"
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"source": [
"-- Isos can be lifted into other structures\n",
"\n",
"mapping' :: Functor f => Iso' s a -> Iso' (f s) (f a)\n",
"mapping' i = iso (fmap (view i)) (fmap (review i))\n",
"\n",
"-- mapping :: (Functor f, Functor g)\n",
"-- => Iso s t a b -> Iso (f s) (g t) (f a) (g b)\n",
"\n",
":t mapping\n",
"\n",
"-- contramapping :: Contravariant f\n",
"-- => Iso s t a b -> Iso (f a) (f b) (f s) (f t)\n",
"\n",
"-- bimapping :: (Bifunctor f, Bifunctor g)\n",
"-- => Iso s t a b -> Iso s' t' a' b'\n",
"-- -> Iso (f s s') (g t t') (f a a') (g b b')\n",
" \n",
"-- dimapping :: (Profunctor p, Profunctor q)\n",
"-- => Iso s t a b -> Iso s' t' a' b'\n",
"-- -> Iso (p a s') (q b t') (p s a') (q t b')\n",
"\n",
"-- Even more simplified signatures\n",
"\n",
"-- contramapping :: (Contravariant f)\n",
"-- => Iso' s a -> Iso (f a) (f s)\n",
"\n",
"-- bimapping :: (Bifunctor f)\n",
"-- => Iso' s a -> Iso' s' a'\n",
"-- -> Iso' (f s s') (f a a')\n",
"\n",
"-- dimapping :: (Profunctor p)\n",
"-- => Iso' s a -> Iso' s' a'\n",
"-- -> Iso' (p a s') (p s a')"
]
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"cell_type": "markdown",
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"source": [
"## Isos and newtypes"
]
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"cell_type": "code",
"execution_count": 133,
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{
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"Email {_email = \"joe@example.com\"}"
]
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"UserID \"joe@example.com\""
]
},
"metadata": {},
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"}\n",
".hoogle-code {\n",
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"color: green;\n",
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"font-family: monospace;\n",
"margin-left: 1em;\n",
"}\n",
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"font-family: monospace;\n",
"display: block;\n",
"}\n",
".err-msg {\n",
"color: red;\n",
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"</style><span class='get-type'>coerced :: forall (p :: * -> * -> *) (f :: * -> *) s a t b. (Profunctor p, Functor f, Coercible s a, Coercible t b) => p a (f b) -> p s (f t)</span>"
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"Email {_email = \"moc.elpmaxe@eoj\"}"
]
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"source": [
"{-# LANGUAGE TemplateHaskell #-}\n",
"\n",
"import Data.Coerce (coerce)\n",
"import Data.Char as C\n",
"\n",
":t coerce\n",
"\n",
"newtype Email = Email {_email :: String}\n",
" deriving (Show)\n",
"makeLenses ''Email\n",
"\n",
"coerce (\"joe@example.com\" :: String) :: Email\n",
"\n",
"coerce (Email \"joe@example.com\") :: UserID\n",
"\n",
"-- coerced :: (Coercible s a, Coercible t b) => Iso s t a b\n",
"\n",
":t coerced\n",
"\n",
"over coerced\n",
" (Prelude.reverse :: String -> String)\n",
" (Email \"joe@example.com\") :: Email\n",
" \n",
"\n",
"-- Email \"joe@example.com\" & email . (traversed %~ C.toUpper)"
]
},
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"cell_type": "markdown",
"metadata": {},
"source": [
"## Newtype wrapper Isos"
]
},
{
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"execution_count": 2,
"metadata": {},
"outputs": [],
"source": [
"-- _Wrapped' :: Wrapped s => Iso' s (Unwrapped s)\n",
"-- _Unwrapped' :: Wrapped s => Iso' (Unwrapped s) s\n",
"\n",
"-- Not automatically derived."
]
}
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Reference in a new issue Copy permalink