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diff --git a/users/tazjin/aoc2020/default.nix b/users/tazjin/aoc2020/default.nix
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+# Solutions for Advent of Code 2020, written in Emacs Lisp.
+#
+# For each day a new file is created as "solution-day$n.el".
+{ depot, pkgs, ... }:
+
+let
+  inherit (builtins) attrNames filter head listToAttrs match readDir;
+  dir = readDir ./.;
+  matchSolution = match "solution-(.*)\.el";
+  isSolution = f: (matchSolution f) != null;
+  getDay = f: head (matchSolution f);
+
+  solutionFiles = filter (e: dir."${e}" == "regular" && isSolution e) (attrNames dir);
+  solutions = map
+    (f:
+      let day = getDay f; in depot.nix.writeElispBin {
+        name = day;
+        deps = p: with p; [ dash s ht p.f ];
+        src = ./. + ("/" + f);
+      })
+    solutionFiles;
+in
+pkgs.symlinkJoin {
+  name = "aoc2020";
+  paths = solutions;
+}