Initial commit

.envrc

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+use flake

.gitignore

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+.bsp
+.direnv
+.metals
+.scala-build
+secrets.env
+out

.scalafmt.conf

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+version = "3.7.17"
+runner.dialect = scala3

build.mill

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+package build
+import mill.*, scalalib.*
+
+object core extends ScalaModule:
+  def scalaVersion = "3.7.2"
+  def scalacOptions = Seq("-Wunused:all")

core/src/main.scala

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+import scala.collection.immutable.ArraySeq
+
+@main
+def main =
+  val temlate = Template(TestLiveView.render)
+  println(temlate.init(MyModel("Initial title")))
+  println(temlate.update(MyModel("Updated title")))
+
+trait LiveView[Model]:
+  val model = Dyn[Model, Model](identity)
+  def render: HtmlTag[Model]
+
+final case class MyModel(title: String)
+
+object TestLiveView extends LiveView[MyModel]:
+  def render: HtmlTag[MyModel] =
+    div(
+      div("some text"),
+      model(_.title)
+    )
+
+class Dyn[I, O](f: I => O):
+  private var last: Option[O] = None
+
+  def apply[O2](f2: O => O2): Dyn[I, O2] = Dyn(f.andThen(f2))
+
+  def forceUpate(v: I): O =
+    val newValue = f(v)
+    last = Some(newValue)
+    newValue
+
+  def update(v: I): Option[O] =
+    val newValue = f(v)
+    last match
+      case Some(lastValue) if lastValue == newValue => None
+      case _ =>
+        last = Some(newValue)
+        last
+
+enum Mod[T]:
+  case Tag(v: HtmlTag[T])
+  case Text(v: String)
+  case DynText(v: Dyn[T, String])
+
+given [T]: Conversion[HtmlTag[T], Mod[T]] = Mod.Tag(_)
+given [T]: Conversion[String, Mod[T]] = Mod.Text(_)
+given [T]: Conversion[Dyn[T, String], Mod[T]] = Mod.DynText(_)
+
+class Template[Model](
+    private val static: ArraySeq[String],
+    private val dynamic: ArraySeq[Dyn[Model, String]]
+):
+  def init(model: Model): Template.InitialState =
+    Template.InitialState(
+      static,
+      dynamic.map(_.forceUpate(model))
+    )
+  def update(model: Model): Template.Diff =
+    Template.Diff(
+      dynamic.zipWithIndex.flatMap((dyn, i) => dyn.update(model).map(i -> _))
+    )
+object Template:
+  final case class InitialState(static: Seq[String], dynamic: Seq[String])
+  final case class Diff(dynamic: Seq[(Int, String)])
+  def apply[Model](tag: HtmlTag[Model]) =
+    val (static, dynamic) = buildTag(tag)
+    new Template(static.to(ArraySeq), dynamic.to(ArraySeq))
+
+def buildMod[Model](mod: Mod[Model]): (List[String], List[Dyn[Model, String]]) =
+  mod match
+    case Mod.Tag(v)            => buildTag(v)
+    case Mod.Text(v)           => (List(v), List.empty)
+    case Mod.DynText[Model](v) => (List.empty, List(v))
+
+def buildTag[Model](
+    tag: HtmlTag[Model]
+): (List[String], List[Dyn[Model, String]]) =
+  val modsBuilt: List[(List[String], List[Dyn[Model, String]])] =
+    tag.mods.map(buildMod)
+  val static =
+    List(s"<${tag.name}>") ++
+      modsBuilt.flatMap(_._1) ++
+      List(s"</${tag.name}>")
+  val dynamic = modsBuilt.flatMap(_._2)
+  (static, dynamic)
+
+trait HtmlTag[Model]:
+  def name: String
+  def mods: List[Mod[Model]]
+
+class Div[Model](val mods: List[Mod[Model]]) extends HtmlTag[Model]:
+  val name = "div"
+
+def div[Model](mods: Mod[Model]*): Div[Model] = Div(mods.toList)

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1753939845,
+        "narHash": "sha256-K2ViRJfdVGE8tpJejs8Qpvvejks1+A4GQej/lBk5y7I=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "94def634a20494ee057c76998843c015909d6311",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    { nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        mill = pkgs.mill.overrideAttrs (old: rec {
+          version = "1.0.2";
+          src = pkgs.fetchurl {
+            url = "https://repo1.maven.org/maven2/com/lihaoyi/mill-dist-native-linux-amd64/${version}/mill-dist-native-linux-amd64-${version}.exe";
+            hash = "sha256-+jRVJDxpH9DONuar+1CqB0Yl6thAuTn7dJYqOEsebGU=";
+          };
+          buildInputs = [ pkgs.zlib ];
+          nativeBuildInputs = [
+            pkgs.makeWrapper
+          ]
+          ++ pkgs.lib.optional pkgs.stdenvNoCC.isLinux pkgs.autoPatchelfHook;
+
+          installPhase = ''
+            runHook preInstall
+
+            install -Dm 555 $src $out/bin/.mill-wrapped
+            # can't use wrapProgram because it sets --argv0
+            makeWrapper $out/bin/.mill-wrapped $out/bin/mill \
+              --prefix PATH : "${pkgs.jre}/bin" \
+              --set-default JAVA_HOME "${pkgs.jre}"
+
+            runHook postInstall
+          '';
+          doInstallCheck = false;
+        });
+      in
+      {
+        devShell = pkgs.mkShell {
+          buildInputs = [
+            mill
+            pkgs.scalafmt
+          ];
+        };
+      }
+    );
+}