Merge pull request #217 from nbuilding/match-fix

Stop double defaults in `match`
nbuilding · Jul 10, 2021 · 34bd5b6 · 34bd5b6
2 parents 5b65fe6 + 109d6d2
commit 34bd5b6
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diff --git a/python/run.n b/python/run.n
@@ -1 +1,7 @@
-print(["12", "1", "2"][1][1])
+print(match ("Why are you?") {
+  "Who are you?" -> "I am an example."
+  "How are you?" -> "I am good."
+  "Why are you?" -> "Why are *you*?"
+  "Why are you?" -> "Why are *youu*?"
+  _ -> "I don't understand."
+})
diff --git a/python/scope.py b/python/scope.py
@@ -1725,6 +1725,23 @@ def type_check_expr(self, expr):
             first_value_type = self.type_check_expr(first_value)
             for i, match_value in enumerate(match_block.children):
                 match, value = match_value.children
+
+                if (
+                    i != len(match_block.children) - 1
+                    and isinstance(match, lark.Tree)
+                    and len(match.children) == 1
+                    and isinstance(match.children[0], lark.Token)
+                    and match.children[0].type == "NAME"
+                    and match.children[0].value == "_"
+                ):
+                    self.errors.append(
+                        TypeCheckError(
+                            match,
+                            "You cannot have more than one default in a match statement"
+                        )
+                    )
+                    continue
+
                 if (
                     i != len(match_block.children) - 1
                     and self.type_check_expr(match) != first_match_type