Cosmetics in stdlib

stdlib/Ostap.lama

@@ -1,3 +1,9 @@
+-- Ostap.
+-- (C) Dmitry Boulytchev, JetBrains Research, St. Petersburg State University, 2020
+--
+-- This unit provides an implementation of monadic parser combinators in CPS with
+-- memoization.
+
 import List;
 import Collection;
 import Ref;
@@ -226,4 +232,66 @@ public fun parseString (p, s) {
   acc.result
 }
 
+public fun left (f) {
+  fun (c, x) {
+     fun (y) {
+       f (c (x), y)
+     }
+  }
+}
+
+public fun right (f) {
+  fun (c, x) {
+    fun (y) {
+      c (f (x, y))
+    }
+  }
+}
+
+--- ops -> fun (x, y) {x `op` y}
+fun altl (level) {
+  case level of
+    [assoc, ps] ->
+       local assfun = case assoc of Left -> left | Right -> right | Nona -> left esac;
+       case map (fun (p) {
+                   case p of
+                     [op, sema] -> op @ lift(assfun (sema))
+                   esac
+                 }, ps) of
+         p : ps -> foldl (infix |, p, ps)
+       esac
+  esac
+}
+
+public fun expr (ops, opnd) {
+  fun inner (ops) {
+    case ops of
+      {}         -> fun (c) {opnd @ c}
+    | level : tl ->
+        local lops = altl (level),
+              next = inner (tl);
+
+        case level.fst of
+          Nona ->
+           fun this (c) {
+             next (id) |> fun (l) {lops |> fun (op) {next (id) @ fun (r) {c (op)(id, l)(r)}}}
+           | next (id) @ c
+           }
+
+           this
+
+        | _    ->
+           fun this (c) {
+             next (id) |> fun (l) {lops |> fun (op) {this (op (c, l))}}
+           | next (id) @ c
+           }
+
+           this
+        esac
+    esac  
+  }
+
+  inner (ops)
+}
+
 initOstap ()