From d038bc439d8b0801671546e73471cb03279d7852 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sat, 25 Feb 2023 10:40:15 -0500
Subject: Allow lookup* to return a default.

---
 chickadee/graphics/seagull.scm | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/chickadee/graphics/seagull.scm b/chickadee/graphics/seagull.scm
index d03de86..abd4429 100644
--- a/chickadee/graphics/seagull.scm
+++ b/chickadee/graphics/seagull.scm
@@ -142,8 +142,12 @@
         (make-exception-with-message "seagull: unbound variable")
         (make-exception-with-irritants (list name (env-names env)))))))
 
-(define (lookup* name env)
-  (assq-ref env name))
+(define* (lookup* name env #:optional default)
+  (let loop ((env env))
+    (match env
+      (() default)
+      (((k . v) . rest)
+       (if (eq? k name) v (loop rest))))))
 
 (define (lookup-all names env)
   (map (lambda (name) (lookup name env)) names))
-- 
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