more descriptive exception values

Author: ramalho

mylis/mylis_3/listypes.py

@@ -1,15 +1,17 @@
 #!/usr/bin/env python3
 
-################ lis.py: Scheme Interpreter in Python 3.10
-## (c) Peter Norvig, 2010-18; See http://norvig.com/lispy.html
+################ Scheme Interpreter in Python 3.10
+## Based on lis.py (c) Peter Norvig, 2010-18
+## See http://norvig.com/lispy.html
 ## Refactorting and additions by Luciano Ramalho (2022)
 
-from .listypes import (
+from .lis_types import (
     Atom,
     Symbol,
     Expression,
+    BlankExpression,
+    BraceNeverClosed,
     UnexpectedCloseBrace,
-    UnexpectedEndOfSource,
 )
 
 
@@ -38,17 +40,17 @@ def read_from_tokens(tokens: list[str]) -> Expression:
     try:
         token = tokens.pop(0)
     except IndexError:
-        raise UnexpectedEndOfSource()
+        raise BlankExpression()
     if token in BRACES:
         exp = []
         while tokens and tokens[0] != BRACES[token]:
             exp.append(read_from_tokens(tokens))
         if not tokens:
-            raise UnexpectedEndOfSource()
+            raise BraceNeverClosed(token)
         tokens.pop(0)  # discard close brace
         return exp
     elif token in CLOSE_BRACES:
-        raise UnexpectedCloseBrace()
+        raise UnexpectedCloseBrace(token)
     else:
         return parse_atom(token)
 

mylis/mylis_3/parser.py

@@ -1,8 +1,9 @@
-from .listypes import (
+from .lis_types import (
+    BlankExpression,
     Expression,
     ParserException,
     UnexpectedCloseBrace,
-    UnexpectedEndOfSource,
+    BraceNeverClosed,
 )
 from .parser import parse
 
@@ -64,15 +65,19 @@ def test_parse_mixed_braces(source: str, expected: Expression) -> None:
 
 
 @mark.parametrize(
-    'source, expected',
+    'source, expected, brace',
     [
-        ('', UnexpectedEndOfSource),
-        ('(', UnexpectedEndOfSource),
-        ('([]', UnexpectedEndOfSource),
-        ('(])', UnexpectedCloseBrace),
-        ('([)', UnexpectedCloseBrace),
+        ('', BlankExpression, ''),
+        ('{', BraceNeverClosed, '{'),
+        ('([]', BraceNeverClosed, '('),
+        ('(])', UnexpectedCloseBrace, ']'),
+        ('([)', UnexpectedCloseBrace, ')'),
     ],
 )
-def test_parse_malformed(source: str, expected: ParserException) -> None:
-    with raises(expected):  # type: ignore
+def test_parse_malformed(
+    source: str, expected: ParserException, brace: str
+) -> None:
+    with raises(expected) as excinfo:  # type: ignore
         parse(source)
+    if brace:
+        assert repr(brace) in str(excinfo.value)