1 files changed, 82 insertions, 0 deletions
diff --git a/users/sterni/nix/flow/default.nix b/users/sterni/nix/flow/default.nix
new file mode 100644
index 000000000000..b5783bd86deb
--- /dev/null
+++ b/users/sterni/nix/flow/default.nix
@@ -0,0 +1,82 @@
+{ depot, ... }:
+
+let
+
+  inherit (depot.nix)
+    yants
+    ;
+
+  inherit (depot.users.sterni.nix)
+    fun
+    ;
+
+  # we must avoid evaluating any of the sublists
+  # as they may contain conditions that throw
+  condition = yants.restrict "condition"
+    (ls: builtins.length ls == 2)
+    (yants.list yants.any);
+
+  /* Like the common lisp macro: takes a list
+     of two elemented lists whose first element
+     is a boolean. The second element of the
+     first list that has true as its first
+     element is returned.
+
+     Type: [ [ bool a ] ] -> a
+
+     Example:
+
+     cond [
+       [ (builtins.isString true) 12 ]
+       [ (3 == 2) 13 ]
+       [ true 42 ]
+     ]
+
+     => 42
+   */
+  cond = conds: switch true conds;
+
+  /* Generic pattern match-ish construct for nix.
+     Takes a bunch of lists which are of length
+     two and checks the first element for either
+     a predicate or a value. The second value of
+     the first list which either has a value equal
+     to or a function that evaluates to true for
+     the given value.
+
+     Type: a -> [ [ (function | a) b ] ] -> b
+
+     Example:
+
+     switch "foo" [
+       [ "smol" "SMOL!!!" ]
+       [ (x: builtins.stringLength x <= 3) "smol-ish" ]
+       [ (fun.const true) "not smol" ]
+      ]
+
+      => "smol-ish"
+  */
+  switch = x: conds:
+    if builtins.length conds == 0
+    then builtins.throw "exhausted all conditions"
+    else
+      let
+        c = condition (builtins.head conds);
+        s = builtins.head c;
+        b =
+          if builtins.isFunction s
+          then s x
+          else x == s;
+      in
+        if b
+        then builtins.elemAt c 1
+        else switch x (builtins.tail conds);
+
+
+
+in {
+  inherit
+    cond
+    switch
+    ;
+}