diff --git a/modules/lib/types-dag.nix b/modules/lib/types-dag.nix
new file mode 100644
index 000000000..4003d7132
--- /dev/null
+++ b/modules/lib/types-dag.nix
@@ -0,0 +1,96 @@
+{ dag, lib }:
+
+with lib;
+
+let
+
+  isDagEntry = e: isAttrs e && (e ? data) && (e ? after) && (e ? before);
+
+  dagContentType = elemType: types.submodule {
+    options = {
+      data = mkOption { type = elemType; };
+      after = mkOption { type = with types; uniq (listOf str); };
+      before = mkOption { type = with types; uniq (listOf str); };
+    };
+  };
+
+in
+
+{
+  # A directed acyclic graph of some inner type.
+  dagOf = elemType:
+    let
+      convertAllToDags =
+        let
+          maybeConvert = n: v:
+            if isDagEntry v
+            then v
+            else dag.entryAnywhere v;
+        in
+          map (def: def // { value = mapAttrs maybeConvert def.value; });
+
+      attrEquivalent = types.attrsOf (dagContentType elemType);
+    in
+      mkOptionType rec {
+        name = "dagOf";
+        description = "DAG of ${elemType.description}s";
+        check = isAttrs;
+        merge = loc: defs: attrEquivalent.merge loc (convertAllToDags defs);
+        getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name>"]);
+        getSubModules = elemType.getSubModules;
+        substSubModules = m: dagOf (elemType.substSubModules m);
+        functor = (defaultFunctor name) // { wrapped = elemType; };
+      };
+
+  # A directed acyclic graph of some inner type OR a list of that
+  # inner type. This is a temporary hack for use by the
+  # `programs.ssh.matchBlocks` and is only guaranteed to be vaguely
+  # correct!
+  #
+  # In particular, adding a dependency on one of the "unnamed-N-M"
+  # entries generated by a list value is almost guaranteed to destroy
+  # the list's order.
+  #
+  # This function will be removed in version 20.09.
+  listOrDagOf = elemType:
+    let
+      paddedIndexStr = list: i:
+        let
+          padWidth = stringLength (toString (length list));
+        in
+          fixedWidthNumber padWidth i;
+
+      convertAllToDags = defs:
+        let
+          convertAttrValue = n: v:
+            if isDagEntry v then v
+            else dag.entryAnywhere v;
+
+          convertListValue = namePrefix: vs:
+            let
+              pad = paddedIndexStr vs;
+              makeEntry = i: v:
+                nameValuePair "${namePrefix}.${pad i}" (dag.entryAnywhere v);
+            in
+              listToAttrs (imap1 makeEntry vs);
+
+          convertValue = i: value:
+            if isList value
+            then convertListValue "unnamed-${paddedIndexStr defs i}" value
+            else mapAttrs convertAttrValue value;
+        in
+          imap1 (i: def: def // { value = convertValue i def.value; }) defs;
+
+      attrEquivalent = types.attrsOf (dagContentType elemType);
+    in
+      mkOptionType rec {
+        name = "dagOf";
+        description = "DAG of ${elemType.description}s";
+        check = x: isAttrs x || isList x;
+        merge = loc: defs: attrEquivalent.merge loc (convertAllToDags defs);
+        getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["<name>"]);
+        getSubModules = elemType.getSubModules;
+        substSubModules = m: dagOf (elemType.substSubModules m);
+        functor = (defaultFunctor name) // { wrapped = elemType; };
+      };
+}
diff --git a/modules/lib/types.nix b/modules/lib/types.nix
index 1b514d20a..da8b7d4f2 100644
--- a/modules/lib/types.nix
+++ b/modules/lib/types.nix
@@ -1,9 +1,18 @@
-{ lib }:
+{ lib, dag ? import ./dag.nix { inherit lib; } }:
 
 with lib;
 
+let
+
+  hmLib = import ./default.nix { inherit lib; };
+  typesDag = import ./types-dag.nix { inherit dag lib; };
+
+in
+
 {
 
+  inherit (typesDag) dagOf listOrDagOf;
+
   selectorFunction = mkOptionType {
     name = "selectorFunction";
     description =
diff --git a/tests/default.nix b/tests/default.nix
index 95a0f16bc..6f2b5ec04 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -34,6 +34,7 @@ import nmt {
     // import ./modules/services/sxhkd
     // import ./modules/systemd
   )
+  // import ./lib/types
   // import ./modules/files
   // import ./modules/home-environment
   // import ./modules/misc/fontconfig
diff --git a/tests/lib/types/dag-merge-result.txt b/tests/lib/types/dag-merge-result.txt
new file mode 100644
index 000000000..9779ef13c
--- /dev/null
+++ b/tests/lib/types/dag-merge-result.txt
@@ -0,0 +1,3 @@
+before:before
+between:between
+after:after
diff --git a/tests/lib/types/dag-merge.nix b/tests/lib/types/dag-merge.nix
new file mode 100644
index 000000000..c5b884b64
--- /dev/null
+++ b/tests/lib/types/dag-merge.nix
@@ -0,0 +1,39 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  dag = config.lib.dag;
+  hmTypes = import ../../../modules/lib/types.nix { inherit dag lib; };
+
+  result =
+    let
+      sorted = dag.topoSort config.tested.dag;
+      data = map (e: "${e.name}:${e.data}") sorted.result;
+    in
+      concatStringsSep "\n" data + "\n";
+
+in
+
+{
+  options.tested.dag = mkOption {
+    type = with types; hmTypes.dagOf str;
+  };
+
+  config = {
+    tested = mkMerge [
+      { dag.after = dag.entryAnywhere "after"; }
+      { dag.before = dag.entryBefore ["after"] "before"; }
+      { dag.between = dag.entryBetween ["after"] ["before"] "between"; }
+    ];
+
+    home.file."result.txt".text = result;
+
+    nmt.script = ''
+      assertFileContent \
+        home-files/result.txt \
+        ${./dag-merge-result.txt}
+    '';
+  };
+}
diff --git a/tests/lib/types/default.nix b/tests/lib/types/default.nix
new file mode 100644
index 000000000..9fce65f88
--- /dev/null
+++ b/tests/lib/types/default.nix
@@ -0,0 +1,4 @@
+{
+  lib-types-dag-merge = ./dag-merge.nix;
+  lib-types-list-or-dag-merge = ./list-or-dag-merge.nix;
+}
diff --git a/tests/lib/types/list-or-dag-merge-result.txt b/tests/lib/types/list-or-dag-merge-result.txt
new file mode 100644
index 000000000..5fb67a510
--- /dev/null
+++ b/tests/lib/types/list-or-dag-merge-result.txt
@@ -0,0 +1,15 @@
+before:before
+between:between
+after:after
+unnamed-1.1:k
+unnamed-1.2:l
+unnamed-2.01:a
+unnamed-2.02:b
+unnamed-2.03:c
+unnamed-2.04:d
+unnamed-2.05:e
+unnamed-2.06:f
+unnamed-2.07:g
+unnamed-2.08:h
+unnamed-2.09:i
+unnamed-2.10:j
diff --git a/tests/lib/types/list-or-dag-merge.nix b/tests/lib/types/list-or-dag-merge.nix
new file mode 100644
index 000000000..3f4cd0ce5
--- /dev/null
+++ b/tests/lib/types/list-or-dag-merge.nix
@@ -0,0 +1,41 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  dag = config.lib.dag;
+  hmTypes = import ../../../modules/lib/types.nix { inherit dag lib; };
+
+  result =
+    let
+      sorted = dag.topoSort config.tested.dag;
+      data = map (e: "${e.name}:${e.data}") sorted.result;
+    in
+      concatStringsSep "\n" data + "\n";
+
+in
+
+{
+  options.tested.dag = mkOption {
+    type = with types; hmTypes.listOrDagOf str;
+  };
+
+  config = {
+    tested = mkMerge [
+      { dag = [ "k" "l" ]; }
+      { dag = [ "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" ]; }
+      { dag.after = dag.entryAnywhere "after"; }
+      { dag.before = dag.entryBefore ["after"] "before"; }
+      { dag.between = dag.entryBetween ["after"] ["before"] "between"; }
+    ];
+
+    home.file."result.txt".text = result;
+
+    nmt.script = ''
+      assertFileContent \
+        home-files/result.txt \
+        ${./list-or-dag-merge-result.txt}
+    '';
+  };
+}