Fixes #7 : Add an error message when a reference cannot be resolved.

Author: green-coder

CHANGELOG.md

@@ -10,6 +10,8 @@ Versions prior to v0.1.0 are considered experimental, their API may change.
 ### Fixed
 - :fn with-condition in the `describe` function.
   Updated the minimap model to reflect that with-condition is valid for the :fn nodes.
+- Throw an error when a reference cannot be resolved in the model, instead of just let
+  minimallist crash somewhere else with an unexpected `nil` model.
 
 ## [0.0.6] - 2020-08-09
 ## [0.0.5] - 2020-08-09

src/minimallist/core.cljc

@@ -41,6 +41,11 @@
      ~consequence
      true))
 
+(defn- resolve-ref [context key]
+  (when-not (contains? context key)
+   (throw (ex-info "Cannot resolve reference." {:context context, :key key})))
+  (get context key))
+
 (declare -valid?)
 
 (defn- left-overs
@@ -68,7 +73,7 @@
                    (drop (:min model))
                    (apply concat))
       :let (left-overs (into context (:bindings model)) (:body model) seq-data)
-      :ref (left-overs context (get context (:key model)) seq-data))
+      :ref (left-overs context (resolve-ref context (:key model)) seq-data))
     (if (and seq-data
              (-valid? context (dissoc model :inlined) (first seq-data)))
       [(next seq-data)]
@@ -132,7 +137,7 @@
                         (implies (contains? model :condition-model)
                                  (-valid? context (:condition-model model) data)))
     :let (-valid? (into context (:bindings model)) (:body model) data)
-    :ref (-valid? context (get context (:key model)) data)))
+    :ref (-valid? context (resolve-ref context (:key model)) data)))
 
 (declare -describe)
 
@@ -185,7 +190,7 @@
                    (reverse) ; longest repetitions first
                    (apply concat))
       :let (sequence-descriptions (into context (:bindings model)) (:body model) seq-data)
-      :ref (sequence-descriptions context (get context (:key model)) seq-data))
+      :ref (sequence-descriptions context (resolve-ref context (:key model)) seq-data))
     (if seq-data
       (let [description (-describe context (dissoc model :inlined) (first seq-data))]
         (if (:valid? description)
@@ -311,7 +316,7 @@
                          {:valid? false}))
                      {:valid? false})
     :let (-describe (into context (:bindings model)) (:body model) data)
-    :ref (-describe context (get context (:key model)) data)))
+    :ref (-describe context (resolve-ref context (:key model)) data)))
 
 ;; TODO: Treat the attributes independently of the type of the node in which they appear.
 ;;       That's a kind of composition pattern a-la-unity.

test/minimallist/core_test.cljc

@@ -253,7 +253,10 @@
       (doseq [data valid-coll]
         (is (valid? model data)))
       (doseq [data invalid-coll]
-        (is (not (valid? model data)))))))
+        (is (not (valid? model data))))))
+
+  (is (thrown? #?(:clj Exception :cljs js/Object)
+               (valid? (h/let [] (h/ref 'foo)) 'bar))))
 
 
 (deftest describe-test
@@ -477,4 +480,7 @@
     (doseq [[model data-description-pairs] (partition 2 test-data)]
       (doseq [[data description] (partition 2 data-description-pairs)]
         (is (= [data (describe model data)]
-               [data description]))))))
+               [data description])))))
+
+  (is (thrown? #?(:clj Exception :cljs js/Object)
+             (describe (h/let [] (h/ref 'foo)) 'bar))))