catch malformed Pattern

mathics/builtin/base.py

@@ -721,11 +721,17 @@ def boxes_to_tex(self, leaves, **options) -> str:
 class PatternError(Exception):
     def __init__(self, name, tag, *args):
         super().__init__()
+        self.name = name
+        self.tag = tag
+        self.args = args
 
 
 class PatternArgumentError(PatternError):
     def __init__(self, name, count, expected):
         super().__init__(None, None)
+        self.name = name
+        self.count = count
+        self.expected = expected
 
 
 class PatternObject(InstanceableBuiltin, Pattern):

mathics/builtin/patterns.py

@@ -45,7 +45,9 @@
     Integer,
     Rational,
     Real,
+    SymbolFalse,
     SymbolList,
+    SymbolTrue,
 )
 from mathics.core.rules import Rule
 from mathics.core.pattern import Pattern, StopGenerator
@@ -451,6 +453,9 @@ class PatternTest(BinaryOperator, PatternObject):
      = True
     >> MatchQ[-3, _Integer?(#>0&)]
      = False
+    >> MatchQ[3, Pattern[3]]
+     : First element in pattern Pattern[3] is not a valid pattern name.
+     = False
     """
 
     operator = "?"
@@ -660,16 +665,23 @@ class MatchQ(Builtin):
      = False
     >> MatchQ[_Integer][123]
      = True
+    >> MatchQ[3, Pattern[3]]
+     : First element in pattern Pattern[3] is not a valid pattern name.
+     = False
     """
 
     rules = {"MatchQ[form_][expr_]": "MatchQ[expr, form]"}
 
     def apply(self, expr, form, evaluation):
         "MatchQ[expr_, form_]"
 
-        if match(expr, form, evaluation):
-            return Symbol("True")
-        return Symbol("False")
+        try:
+            if match(expr, form, evaluation):
+                return SymbolTrue
+            return SymbolFalse
+        except PatternError as e:
+            evaluation.message(e.name, e.tag, *(e.args))
+            return SymbolFalse
 
 
 class Verbatim(PatternObject):
@@ -801,10 +813,13 @@ class Pattern_(PatternObject):
     }
 
     def init(self, expr):
-        super(Pattern_, self).init(expr)
-        self.varname = expr.leaves[0].get_name()
-        if self.varname is None:
+        if len(expr.leaves) != 2:
+            self.error("patvar", expr)
+        varname = expr.leaves[0].get_name()
+        if varname is None or varname == "":
             self.error("patvar", expr)
+        super(Pattern_, self).init(expr)
+        self.varname = varname
         self.pattern = Pattern.create(expr.leaves[1])
 
     def __repr__(self):