helper functions for handling shell env context manager

shell_env.rkt

@@ -0,0 +1,19 @@
+#lang racket
+
+(define shell-env
+  (make-parameter #hash()))
+
+(define (merge-hash h1 h2)
+  (define h1-vs (hash->list h1))
+  (define h2-vs  (hash->list h2))
+  (make-hash (append h1-vs h2-vs)))
+
+(define (merge-hashes . hs ...)
+  (foldl merge-hash #hash() hs))
+
+(define (set-vars vars)
+  (apply
+    merge-hashes
+    (list
+      (shell-env)
+      (make-hash vars))))