Make ReactElement a proper Monoid and other ergonomic tweaks (#84)

CHANGELOG.md

@@ -5,6 +5,19 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.13.0
+
+### Changed
+* `ReactElement` is now a full `Monoid` with `empty` as identity and append
+  creating React.Fragment elements.
+* **Breaking**: module `Elmish.React.DOM` has been removed and its contents
+  moved to `Elmish.React`.
+* **Breaking**: module `Elmish.Trace` has been removed. Its sole export has been
+  part of the standard `debug` library for a while now.
+* Fixed a bug with `readForeign` and nested `Nullable`s: reading `[1,"foo",2]`
+  as `Nullable (Array Int)` would complain that the second element is bogus
+  (which is true) and incorrectly state that the expected type was `Nullable Int`.
+
 ## 0.12.0
 
 ### Changed

docs/react-ffi.md

@@ -6,9 +6,63 @@ nav_order: 6
 # Using React components
 {:.no_toc}
 
-> **Under construction**. This page is unfinished. Many headings just have some
-> bullet points sketching the main points that should be discussed.
+Because Elmish is just a thin layer on top of React, it is quite easy to use
+non-PureScript React components from the wider ecosystem.
 
-1. TOC
-{:toc}
+A typical import of a React component consists of three parts:
 
+* A row of props, with optional props denoted via `Opt`.
+* Actual FFI-import of the component constructor. This import is weakly
+  typed and shouldn't be exported from the module. Consider it internal
+  implementation detail.
+* Strongly-typed, PureScript-friendly function that constructs the
+  component. The body of such function usually consists of just a call
+  to `createElement` (or `createElement'` for childless components), its
+  only purpose being the type signature. This function is what should be
+  exported for use by consumers.
+
+Classes and type aliases provided in this module, when applied to the
+constructor function, make it possible to pass only partial props to it,
+while still ensuring their correct types and presence of non-optional ones.
+This is facilitated by the
+[undefined-is-not-a-problem](https://github.com/paluh/purescript-undefined-is-not-a-problem/) library.
+
+## Example
+
+### The JSX file with component implementation
+```jsx
+// `world` prop is required, `hello` and `highlight` are optional
+export const MyComponent = ({ hello, world, highlight }) =>
+  <div>
+    <span>{hello || "Hello"}, </span>
+    <span style={ { color: highlight ? "red" : "" } }>{world}</span>
+  </div>
+```
+
+### PureScript FFI module
+```haskell
+module MyComponent(Props, myComponent) where
+
+import Data.Undefined.NoProblem (Opt)
+import Elmish.React (createElement)
+import Elmish.React.Import (ImportedReactComponentConstructor, ImportedReactComponent)
+
+type Props = ( world :: String, hello :: Opt String, highlight :: Opt Boolean )
+
+myComponent :: ImportedReactComponentConstructor Props
+myComponent = createElement myComponent_
+
+foreign import myComponent_ :: ImportedReactComponent
+```
+
+### PureScript use site
+```haskell
+import MyComponent (myComponent)
+import Elmish.React (fragment) as H
+
+view :: ...
+view = H.fragment
+  [ myComponent { world: "world" }
+  , myComponent { hello: "Goodbye", world: "cruel world!", highlight: true }
+  ]
+```

packages.dhall

@@ -8,5 +8,5 @@ in  upstream
   with elmish-html =
     { dependencies = [ "prelude", "record" ]
     , repo = "https://github.com/collegevine/purescript-elmish-html.git"
-    , version = "v0.8.2"
+    , version = "tweaks"
     }

src/Elmish/Component.purs

@@ -28,9 +28,9 @@ import Effect (Effect, foreachE)
 import Effect.Aff (Aff, Milliseconds(..), delay, launchAff_)
 import Effect.Class (class MonadEffect, liftEffect)
 import Elmish.Dispatch (Dispatch)
-import Elmish.React (ReactComponent, ReactComponentInstance, ReactElement, getField, setField)
+import Elmish.React (ReactComponent, ReactComponentInstance, ReactElement)
+import Elmish.React.Internal (Field(..), getField, setField)
 import Elmish.State (StateStrategy, dedicatedStorage, localState)
-import Elmish.Trace (traceTime)
 
 -- | A UI component state transition: wraps the new state value together with a
 -- | (possibly empty) list of effects that the transition has caused (called
@@ -243,10 +243,10 @@ withTrace :: ∀ m msg state
 withTrace def = def { update = tracingUpdate, view = tracingView }
     where
         tracingUpdate s m =
-            let (Transition s cmds) = traceTime "Update" \_ -> def.update s $ Debug.spy "Message" m
+            let (Transition s cmds) = Debug.traceTime "Update" \_ -> def.update s $ Debug.spy "Message" m
             in Transition (Debug.spy "State" s) cmds
         tracingView s d =
-            traceTime "Rendering" \_ -> def.view s d
+            Debug.traceTime "Rendering" \_ -> def.view s d
 
 -- | This function is low level, not intended for a use in typical consumer
 -- | code. Use `construct` or `wrapWithLocalState` instead.
@@ -307,13 +307,13 @@ bindComponent cmpt stateStrategy = \def -> -- Explicit lambda to make sure `def`
           sequence_ =<< getSubscriptions component
           setSubscriptions [] component
 
-        subscriptionsField = "__subscriptions"
-        getSubscriptions = getField @(Array (Effect Unit)) subscriptionsField >>> map (fromMaybe [])
-        setSubscriptions = setField @(Array (Effect Unit)) subscriptionsField
+        subscriptionsField = Field @"__subscriptions" @(Array (Effect Unit))
+        getSubscriptions = getField subscriptionsField >>> map (fromMaybe [])
+        setSubscriptions = setField subscriptionsField
 
-        unmountedField = "__unmounted"
-        getUnmounted = getField @Boolean unmountedField >>> map (fromMaybe false)
-        setUnmounted = setField @Boolean unmountedField
+        unmountedField = Field @"__unmounted" @Boolean
+        getUnmounted = getField unmountedField >>> map (fromMaybe false)
+        setUnmounted = setField unmountedField
 
 -- | Given a `ComponentDef'`, binds that def to a freshly created React class,
 -- | instantiates that class, and returns a rendering function.

src/Elmish/Foreign.purs

@@ -195,7 +195,7 @@ instance CanReceiveFromJavaScript a => CanReceiveFromJavaScript (Nullable a) whe
       | otherwise =
           case validateForeignType @a v of
             Valid -> Valid
-            Invalid err -> Invalid err { expected = "Nullable " <> err.expected }
+            Invalid err -> Invalid err { expected = if err.path == "" then "Nullable " <> err.expected else err.expected }
 
 instance CanPassToJavaScript a => CanPassToJavaScript (Opt a)
 instance CanReceiveFromJavaScript a => CanReceiveFromJavaScript (Opt a) where

src/Elmish/React.js

@@ -19,6 +19,23 @@ export var hydrate_ = ReactDOM.hydrate;
 export var renderToString = (ReactDOMServer && ReactDOMServer.renderToString) || (_ => "");
 export var unmount_ = ReactDOM.unmountComponentAtNode
 
+export var fragment_ = React.Fragment;
+
+export var appendElement_ = a => b => {
+  const childrenOf = x => {
+    if (x === false || x === null || typeof x === 'undefined') return []
+    if (x.type === React.Fragment) {
+      const children = x.props?.children
+      if (children instanceof Array) return children
+      if (children === false || children === null || typeof children === 'undefined') return []
+      return [children]
+    }
+    return [x]
+  }
+  const allChildren = [...childrenOf(a), ...childrenOf(b)]
+  return allChildren.length === 0 ? false : React.createElement(React.Fragment, null, allChildren)
+}
+
 export function createElement_(component, props, children) {
   // The type of `children` is `Array ReactElement`. If we pass that in as
   // third parameter of `React.createElement` directly, React complains about

src/Elmish/React.purs

@@ -1,31 +1,31 @@
 module Elmish.React
-    ( ReactElement
-    , ReactComponent
-    , ReactComponentInstance
-    , class ValidReactProps
-    , class ReactChildren, asReactChildren
-    , assignState
-    , createElement
-    , createElement'
-    , getField
-    , getState
-    , hydrate
-    , setField
-    , setState
-    , render
-    , renderToString
-    , unmount
-    , module Ref
-    ) where
+  ( ReactElement
+  , ReactComponent
+  , ReactComponentInstance
+  , class ValidReactProps
+  , class ReactChildren, asReactChildren
+  , assignState
+  , createElement
+  , createElement'
+  , empty
+  , fragment
+  , getState
+  , hydrate
+  , setState
+  , render
+  , renderToString
+  , text
+  , unmount
+  , module Ref
+  ) where
 
 import Prelude
 
 import Data.Function.Uncurried (Fn3, runFn3)
-import Data.Maybe (Maybe)
 import Data.Nullable (Nullable)
 import Effect (Effect)
 import Effect.Uncurried (EffectFn1, EffectFn2, EffectFn3, runEffectFn1, runEffectFn2, runEffectFn3)
-import Elmish.Foreign (class CanPassToJavaScript, class CanReceiveFromJavaScript, Foreign, readForeign)
+import Elmish.Foreign (class CanPassToJavaScript)
 import Elmish.React.Ref (Ref, callbackRef) as Ref
 import Prim.TypeError (Text, class Fail)
 import Unsafe.Coerce (unsafeCoerce)
@@ -34,6 +34,9 @@ import Web.DOM as HTML
 -- | Instantiated subtree of React DOM. JSX syntax produces values of this type.
 foreign import data ReactElement :: Type
 
+instance Semigroup ReactElement where append = appendElement_
+instance Monoid ReactElement where mempty = empty
+
 -- | This type represents constructor of a React component with a particular
 -- | behavior. The type prameter is the record of props (in React lingo) that
 -- | this component expects. Such constructors can be "rendered" into
@@ -82,6 +85,20 @@ createElement' :: ∀ props
     -> ReactElement
 createElement' component props = createElement component props ([] :: Array ReactElement)
 
+-- | Empty React element.
+empty :: ReactElement
+empty = unsafeCoerce false
+
+-- | Render a plain string as a React element.
+text :: String -> ReactElement
+text = unsafeCoerce
+
+-- | Wraps multiple React elements as a single one (import of React.Fragment)
+fragment :: Array ReactElement -> ReactElement
+fragment = createElement fragment_ {}
+
+foreign import fragment_ :: ReactComponent {}
+foreign import appendElement_ :: ReactElement -> ReactElement -> ReactElement
 
 -- | Asserts that the given type is a valid React props structure. Currently
 -- | there are three rules for what is considered "valid":
@@ -112,14 +129,6 @@ setState :: ∀ state. ReactComponentInstance -> state -> (Effect Unit) -> Effec
 setState = runEffectFn3 setState_
 foreign import setState_ :: ∀ state. EffectFn3 ReactComponentInstance state (Effect Unit) Unit
 
-getField :: ∀ @a. CanReceiveFromJavaScript a => String -> ReactComponentInstance -> Effect (Maybe a)
-getField field object = runEffectFn2 getField_ field object <#> readForeign @a
-foreign import getField_ :: EffectFn2 String ReactComponentInstance Foreign
-
-setField :: ∀ @a. CanPassToJavaScript a => String -> a -> ReactComponentInstance -> Effect Unit
-setField = runEffectFn3 setField_
-foreign import setField_ :: ∀ a. EffectFn3 String a ReactComponentInstance Unit
-
 -- | The equivalent of `this.state = x`, as opposed to `setState`, which is the
 -- | equivalent of `this.setState(x)`. This function is used in a component's
 -- | constructor to set the initial state.

src/Elmish/React/Import.purs

@@ -30,23 +30,23 @@
 -- |
 -- |
 -- |     -- PureScript
--- |     module MyComponent(Props, OptProps, myComponent) where
+-- |     module MyComponent(Props, myComponent) where
 -- |
 -- |     import Data.Undefined.NoProblem (Opt)
 -- |     import Elmish.React (createElement)
 -- |     import Elmish.React.Import (ImportedReactComponentConstructor, ImportedReactComponent)
 -- |
 -- |     type Props = ( world :: String, hello :: Opt String, highlight :: Opt Boolean )
 -- |
--- |     myComponent :: ImportedReactComponentConstructor Props OptProps
+-- |     myComponent :: ImportedReactComponentConstructor Props
 -- |     myComponent = createElement myComponent_
 -- |
 -- |     foreign import myComponent_ :: ImportedReactComponent
 -- |
 -- |
 -- |     -- PureScript use site
 -- |     import MyComponent (myComponent)
--- |     import Elmish.React.DOM (fragment)
+-- |     import Elmish.React (fragment) as H
 -- |
 -- |     view :: ...
 -- |     view = H.fragment

src/Elmish/React/Internal.js

@@ -0,0 +1,2 @@
+export const getField_ = (field, obj) => obj[field]
+export const setField_ = (field, value, obj) => obj[field] = value

src/Elmish/React/Internal.purs

@@ -0,0 +1,25 @@
+module Elmish.React.Internal
+  ( Field(..)
+  , getField
+  , setField
+  ) where
+
+import Prelude
+
+import Data.Maybe (Maybe)
+import Data.Symbol (class IsSymbol, reflectSymbol)
+import Effect (Effect)
+import Effect.Uncurried (EffectFn2, EffectFn3, runEffectFn2, runEffectFn3)
+import Elmish.Foreign (class CanPassToJavaScript, class CanReceiveFromJavaScript, Foreign, readForeign)
+import Elmish.React (ReactComponentInstance)
+import Type.Proxy (Proxy(..))
+
+data Field (f :: Symbol) (a :: Type) = Field
+
+getField :: ∀ f a. CanReceiveFromJavaScript a => IsSymbol f => Field f a -> ReactComponentInstance -> Effect (Maybe a)
+getField _ object = runEffectFn2 getField_ (reflectSymbol $ Proxy @f) object <#> readForeign @a
+foreign import getField_ :: EffectFn2 String ReactComponentInstance Foreign
+
+setField :: ∀ f a. CanPassToJavaScript a => IsSymbol f => Field f a -> a -> ReactComponentInstance -> Effect Unit
+setField _ = runEffectFn3 setField_ $ reflectSymbol $ Proxy @f
+foreign import setField_ :: ∀ a. EffectFn3 String a ReactComponentInstance Unit

src/Elmish/React/Ref.purs

@@ -31,7 +31,13 @@ instance CanPassToJavaScript (Ref a)
 -- | view :: State -> Dispatch Message -> ReactElement
 -- | view state dispatch =
 -- |   H.input_ "" { ref: callbackRef state.inputElement (dispatch <<< RefChanged), … }
+-- |
+-- | update :: State -> Message -> Transition Message State
+-- | update state = case _ of
+-- |   RefChanged ref -> pure state { inputElement = ref }
+-- |   …
 -- | ```
+-- |
 callbackRef :: forall el. Maybe el -> (Maybe el -> Effect Unit) -> Ref el
 callbackRef ref setRef = mkCallbackRef $ mkEffectFn1 \ref' -> case ref, Nullable.toMaybe ref' of
   Nothing, Nothing -> pure unit