Some progress on exception avoidance

src/core/schema.scala

@@ -59,15 +59,17 @@ object JsonValidationError:
       case PatternMismatch(value, pattern) =>
         msg"the value did not conform to the regular expression ${pattern.pattern}"
 
-case class JsonValidationError(issue: JsonValidationError.Issue)
+import JsonValidationError.Issue, Issue.*
+
+case class JsonValidationError(issue: Issue)
 extends Error(msg"the JSON was not valid according to the schema")
 
 trait JsonValueAccessor[NameType <: Label, ValueType]
 extends ValueAccessor[JsonRecord, Maybe[Json], NameType, ValueType]:
   def access(value: Json): ValueType
 
   def transform(value: Maybe[Json], params: List[String]): ValueType =
-    value.mm(access(_)).or(throw JsonValidationError(JsonValidationError.Issue.MissingValue))
+    value.mm(access(_)).or(throw JsonValidationError(MissingValue))
 
 object JsonRecord:
 
@@ -130,28 +132,26 @@ object JsonRecord:
     (value, params) => value.mm(_.as[Text])
 
   given pattern
-      : ValueAccessor[JsonRecord, Maybe[Json], "pattern", Text throws JsonValidationError] with
-    def transform(value: Maybe[Json], params: List[String]): Text throws JsonValidationError =
+      : ValueAccessor[JsonRecord, Maybe[Json], "pattern", Text] with
+    def transform(value: Maybe[Json], params: List[String]): Text =
       value.mm: value =>
         (params: @unchecked) match
           case List(pattern: String) =>
             val regex = Regex(Text(pattern))
             if regex.matches(value.as[Text]) then value.as[Text]
-            else throw JsonValidationError(JsonValidationError.Issue.PatternMismatch(value.as[Text],
-                regex))
-      .or(throw JsonValidationError(JsonValidationError.Issue.MissingValue))
+            else throw JsonValidationError(PatternMismatch(value.as[Text], regex))
+      .or(throw JsonValidationError(MissingValue))
 
-  given maybePattern: ValueAccessor[JsonRecord, Maybe[Json], "pattern?", Maybe[Text] throws
-      JsonValidationError] with
+  given maybePattern: ValueAccessor[JsonRecord, Maybe[Json], "pattern?", Maybe[Text]] with
     def transform
         (value: Maybe[Json], params: List[String] = Nil)
-        : Maybe[Text] throws JsonValidationError =
+        : Maybe[Text] =
       value.mm: value =>
         (params: @unchecked) match
           case pattern :: Nil =>
             val regex = Regex(Text(pattern))
             if regex.matches(value.as[Text]) then value.as[Text]
-            else throw JsonValidationError(JsonValidationError.Issue.PatternMismatch(value.as[Text], regex))
+            else throw JsonValidationError(PatternMismatch(value.as[Text], regex))
 
   given maybeInteger: ValueAccessor[JsonRecord, Maybe[Json], "integer?", Maybe[Int]] =
     (value, params) => value.mm(_.as[Int])

src/test/example.scala

@@ -48,7 +48,7 @@ object ExampleSchema extends JsonSchema(unsafely(Json.parse(t"""{
       "items": {
         "height": { "type": "integer", "description": "Height", "minimum": 1, "maximum": 99 },
         "weight": { "type": "number", "description": "Weight" },
-        "color": { "type": "string", "description": "Colour" }
+        "color": { "type": "string", "description": "Colour", "pattern": "#[0-9a-f]{6}" }
       }
     }
   }

src/test/tests.scala

@@ -36,8 +36,10 @@ object Tests extends Suite(t"Villainy tests"):
         t"""{
           "name": "Jim",
           "sub": { "date": "11/12/20" },
-          "children": [{"height": 100, "weight": 0.8, "color": "green" },
-          {"height": 9, "weight": 30.0, "color": "red"}],
+          "children": [
+            {"height": 100, "weight": 0.8, "color": "green" },
+            {"height": 9, "weight": 30.0, "color": "#ff0000"}
+          ],
           "pattern": "a.b",
           "domain": "example.com"
         }"""
@@ -66,9 +68,13 @@ object Tests extends Suite(t"Villainy tests"):
       record.children.head.weight
     .assert(_ == 0.8)
 
-    test(t"Get a nested item value"):
-      record.children.head.color
-    .assert(_ == t"green")
+    test(t"A bad pattern-checked value throws an exceptions"):
+      unsafely(capture[JsonValidationError, Maybe[Text]](record.children.head.color))
+    .assert(_ == JsonValidationError(JsonValidationError.Issue.PatternMismatch(t"green", r"#[0-9a-f]{6}")))
+
+    test(t"A bad pattern-checked value throws an exceptions"):
+      unsafely(record.children(1).color)
+    .assert(_ == t"#ff0000")
 
     test(t"Get a nested item value"):
       record.sub.date
@@ -78,7 +84,7 @@ object Tests extends Suite(t"Villainy tests"):
       unsafely:
         record.pattern
     .assert(_ == unsafely(Regex(t"a.b")))
-
+    
     test(t"Get some values in a list"):
       unsafely:
         capture: