Backup commit before crunch

examples/maps/map.orc

@@ -0,0 +1,74 @@
+import list
+import option
+import fn::*
+import std::to_string
+import std::debug
+
+-- utilities for using lists as pairs
+
+export fst := \l. (
+  list::get l 0
+    (panic "nonempty expected")
+    \x.x
+)
+export snd := \l. (
+  list::get l 1
+    (panic "2 elements expected")
+    \x.x
+)
+export print_pair := \l. (
+  to_string (fst l) ++ " = " ++ to_string (snd l)
+)
+
+-- constructors
+
+export empty := list::end
+export add := \m.\k.\v. (
+  list::cons
+    list::new[k, v]
+    m
+)
+
+-- queries
+
+-- return the last occurrence of a key if exists
+export get := \m.\k. (
+  loop r on (m) with
+    list::pop m option::none \head.\tail. 
+      if fst head == k
+      then option::some $ snd head
+      else r tail
+)
+
+-- commands
+
+-- remove one occurrence of a key
+export del := \m.\k. (
+  loop r on (m) with
+    list::pop m list::end \head.\tail.
+      if fst head == k then tail
+      else list::cons head $ r tail
+)
+
+-- remove all occurrences of a key
+export clear := \m.\k. (
+  loop r on (m) with
+    list::pop m list::end \head.\tail.
+      if (fst head) == k then r tail
+      else list::cons head $ r tail
+)
+
+-- replace at most one occurrence of a key
+export set := \m.\k.\v. (
+  m
+  |> del k
+  |> add k v
+)
+
+new[...$tail:2, ...$key = ...$value:1] =0x2p333=> (
+  set new[...$tail] (...$key) (...$value)
+)
+new[...$key = ...$value:1] =0x1p333=> (add empty (...$key) (...$value))
+new[] =0x1p333=> empty
+
+export ::(new)