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README.md

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+# Skog
+
+Multiplatform mobile and desktop app framework for [Gren](https://gren-lang.org/).
+
+## Technical notes and references
+
+* Original design plan at ~/projects/gren-multiplatform-experiment/gren-multiplatform.md
+* Proof of concept for iOS at ~/projects/gren-mobile-experiment
+* Driving initial implementation via ~/projects/idlegame-gren
+
+## Other stuff
+
+Skog is Norwegian for "forrest" :)

devbox.json

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+{
+  "packages": [
+    "gren@0.6.5"
+  ]
+}

gren.json

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+{
+    "type": "package",
+    "platform": "browser",
+    "name": "blaix/skog",
+    "summary": "Framework for Gren apps that run on mobile, desktop, and web.",
+    "license": "BSD-3-Clause",
+    "version": "0.1.0",
+    "exposed-modules": [
+        "Skog",
+        "UI",
+        "UI.Attribute",
+        "Mobile",
+        "Desktop"
+    ],
+    "gren-version": "0.6.0 <= v < 0.7.0",
+    "dependencies": {
+        "gren-lang/core": "7.0.0 <= v < 8.0.0",
+        "gren-lang/browser": "6.0.0 <= v < 7.0.0"
+    }
+}

src/Desktop.gren

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+module Desktop exposing (Desktop)
+
+{-| Phantom-type tag for desktop-specific UI elements and views.
+-}
+
+
+type Desktop
+    = Desktop

src/Mobile.gren

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+module Mobile exposing (Mobile)
+
+{-| Phantom-type tag for mobile-specific UI elements and views.
+-}
+
+
+type Mobile
+    = Mobile

src/Skog.gren

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+module Skog exposing (Program, program)
+
+{-| Define a multi-platform Skog program.
+
+The app provides shared `init`, `update`, and `subscriptions` along with
+separate `mobileView` and `desktopView` functions. Bridges (SwiftUI,
+Compose, DOM) consume the views; this stub just wires up a Platform.worker.
+-}
+
+import Desktop exposing (Desktop)
+import Mobile exposing (Mobile)
+import Platform
+import UI
+
+
+type alias Program model msg =
+    Platform.Program {} model msg
+
+
+program :
+    { init : { model : model, command : Cmd msg }
+    , update : msg -> model -> { model : model, command : Cmd msg }
+    , subscriptions : model -> Sub msg
+    , mobileView : model -> UI.Element Mobile msg
+    , desktopView : model -> UI.Element Desktop msg
+    }
+    -> Program model msg
+program config =
+    Platform.worker
+        { init = \_ -> config.init
+        , update = config.update
+        , subscriptions = config.subscriptions
+        }

src/UI.gren

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+module UI exposing
+    ( Element
+    , text
+    , column
+    , row
+    , button
+    , image
+    )
+
+{-| Cross-platform UI primitives.
+
+The `platform` type parameter stays polymorphic for elements that work
+everywhere. Platform-specific elements live in the `Mobile` and `Desktop`
+modules and constrain the parameter.
+-}
+
+import UI.Attribute exposing (Attribute)
+
+
+type Element platform msg
+    = Text
+        { attributes : Array (Attribute platform msg)
+        , content : String
+        }
+    | Column
+        { attributes : Array (Attribute platform msg)
+        , children : Array (Element platform msg)
+        }
+    | Row
+        { attributes : Array (Attribute platform msg)
+        , children : Array (Element platform msg)
+        }
+    | Button
+        { attributes : Array (Attribute platform msg)
+        , onPress : msg
+        , label : Element platform msg
+        }
+    | Image
+        { attributes : Array (Attribute platform msg)
+        , source : String
+        }
+
+
+text : Array (Attribute platform msg) -> String -> Element platform msg
+text attributes content =
+    Text { attributes = attributes, content = content }
+
+
+column :
+    Array (Attribute platform msg)
+    -> Array (Element platform msg)
+    -> Element platform msg
+column attributes children =
+    Column { attributes = attributes, children = children }
+
+
+row :
+    Array (Attribute platform msg)
+    -> Array (Element platform msg)
+    -> Element platform msg
+row attributes children =
+    Row { attributes = attributes, children = children }
+
+
+button :
+    Array (Attribute platform msg)
+    -> { onPress : msg, label : Element platform msg }
+    -> Element platform msg
+button attributes config =
+    Button
+        { attributes = attributes
+        , onPress = config.onPress
+        , label = config.label
+        }
+
+
+image :
+    Array (Attribute platform msg)
+    -> String
+    -> Element platform msg
+image attributes source =
+    Image { attributes = attributes, source = source }

src/UI/Attribute.gren

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+module UI.Attribute exposing (Attribute, padding, backgroundColor)
+
+{-| Styling attributes for UI elements.
+-}
+
+
+type Attribute platform msg
+    = Padding Int
+    | BackgroundColor String
+
+
+padding : Int -> Attribute platform msg
+padding amount =
+    Padding amount
+
+
+backgroundColor : String -> Attribute platform msg
+backgroundColor color =
+    BackgroundColor color