plutils

commit 76c59d52a1a5db2e10db04071b1a35189bc35dec
parent 0d9ba56d82d9a5993d54fb79f38c4e39af7f1b8e
Author: Robert Russell <robert@rr3.xyz>
Date:   Sat, 26 Jul 2025 19:01:27 -0700

Add Environment.eval back

Diffstat:
M
src/PlUtils/Environment.hs
 | 
10
++++++++++

1 file changed, 10 insertions(+), 0 deletions(-)
diff --git a/src/PlUtils/Environment.hs b/src/PlUtils/Environment.hs
@@ -6,8 +6,10 @@ module PlUtils.Environment (
     assign,
     lookup,
     define,
+    eval,
 ) where
 
+import Data.Maybe (fromMaybe)
 import Naturals.NatMap (NatMap)
 import Naturals.NatMap qualified as NatMap
 import Prelude hiding (lookup)
@@ -46,3 +48,11 @@ define :: (Level -> v) -> Environment v -> Environment v
 define makeVal env =
     let (l, env') = bind env
     in assign l (makeVal l) env'
+
+-- | Evaluate an index in an environment, falling back to making a value with
+-- the given function in case the environment doesn't have a substitution for
+-- the index.
+eval :: (Level -> v) -> Index -> Environment v -> v
+eval makeVal i env =
+    let l = idxToLvl (depth env) i
+    in fromMaybe (makeVal l) $ lookup l env