From 3e4e38f6987d7435232b175fd0070608b76b4d50 Mon Sep 17 00:00:00 2001
From: Oliver Reiche <oliver.reiche@huawei.com>
Date: Wed, 24 Aug 2022 18:23:37 +0200
Subject: Rules: Implement hierarchical defaults

---
 CC/EXPRESSIONS | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

(limited to 'CC/EXPRESSIONS')

diff --git a/CC/EXPRESSIONS b/CC/EXPRESSIONS
index d04591f..7ebc8ad 100644
--- a/CC/EXPRESSIONS
+++ b/CC/EXPRESSIONS
@@ -48,6 +48,29 @@
     , "body": {"type": "CALL_EXPRESSION", "name": "provider_list"}
     }
   }
+, "defaults-base-provides":
+  { "doc": ["Query list-provider from 'base' targets (last wins)"]
+  , "vars": ["provider"]
+  , "vars_doc":
+    {"provider": ["The name of the list-provider in the provides map."]}
+  , "imports": {"provider_list": ["./", "..", "field_provider_list"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings": [["fieldname", "base"]]
+    , "body":
+      { "type": "foldl"
+      , "var": "next"
+      , "accum_var": "curr"
+      , "range": {"type": "CALL_EXPRESSION", "name": "provider_list"}
+      , "body":
+        { "type": "if"
+        , "cond": {"type": "var", "name": "next"}
+        , "then": {"type": "var", "name": "next"}
+        , "else": {"type": "var", "name": "curr"}
+        }
+      }
+    }
+  }
 , "configure transition":
   { "vars": ["COMPILER_FAMILY"]
   , "expression":
-- 
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