utils: Add eval-with and eval1-with.

utils.rkt

@@ -2,7 +2,35 @@
 
 (require)
 
-(provide)
+(provide Symbol VariableMapping
+         eval-with eval1-with)
 
 (module+ test
-  (require rackunit))
+  (require typed/rackunit))
+
+;;; ===================
+;;; HashTable injection
+;;; ===================
+
+(define-type Variable Symbol)
+(define-type (VariableMapping A) (Immutable-HashTable Variable A))
+
+(: eval-with (-> (VariableMapping Any) Any AnyValues))
+(define (eval-with ht expr)
+  (parameterize ([current-namespace (make-base-namespace)])
+    (for ([(x val) (in-hash ht)]) (namespace-set-variable-value! x val))
+    (eval expr)))
+
+(: eval1-with (-> (VariableMapping Any) Any Any))
+(define (eval1-with ht expr)
+  (call-with-values (λ () (eval-with ht expr))
+                    (λ args (car args))))
+
+(module+ test
+  (test-case "eval-with"
+    (check-equal? (eval1-with (hash 'a 1 'b 2) '(+ a b 1))
+                  4)
+    (define ht : (VariableMapping Integer) (hash 'a 1 'b 2))
+    (define expr : Any '(+ a b 1))
+    (check-equal? (eval1-with ht expr)
+                  4)))