Add deref literal syntax to the reader (#146)

Author: chrisrink10

basilisp/reader.py

@@ -46,6 +46,7 @@
 
 _APPLY = symbol.symbol('apply', ns='basilisp.core')
 _CONCAT = symbol.symbol('concat', ns='basilisp.core')
+_DEREF = symbol.symbol('deref', ns='basilisp.core')
 _HASH_MAP = symbol.symbol('hash-map', ns='basilisp.core')
 _HASH_SET = symbol.symbol('hash-set', ns='basilisp.core')
 _LIST = symbol.symbol('list', ns='basilisp.core')
@@ -710,6 +711,14 @@ def _read_unquote(ctx: ReaderContext) -> LispForm:
             return llist.l(_UNQUOTE, next_form)
 
 
+def _read_deref(ctx: ReaderContext) -> LispForm:
+    """Read a derefed form from the input stream."""
+    start = ctx.reader.advance()
+    assert start == "@"
+    next_form = _read_next(ctx)
+    return llist.l(_DEREF, next_form)
+
+
 def _read_regex(ctx: ReaderContext) -> Pattern:
     """Read a regex reader macro from the input stream."""
     s = _read_str(ctx)
@@ -826,6 +835,8 @@ def _read_next(ctx: ReaderContext) -> LispForm:  # noqa: C901
         return _read_syntax_quoted(ctx)
     elif token == '~':
         return _read_unquote(ctx)
+    elif token == '@':
+        return _read_deref(ctx)
     elif token == '':
         return __EOF
     else:

tests/reader_test.py

@@ -667,6 +667,12 @@ def test_function_reader_macro():
         read_str_first("#app/ermagrd [1 2 3]")
 
 
+def test_deref():
+    assert read_str_first("@s") == llist.l(reader._DEREF, sym.symbol('s'))
+    assert read_str_first("@ns/s") == llist.l(reader._DEREF, sym.symbol('s', ns='ns'))
+    assert read_str_first("@(atom {})") == llist.l(reader._DEREF, llist.l(sym.symbol('atom'), lmap.Map.empty()))
+
+
 def test_regex_reader_literal():
     assert read_str_first('#"hi"') == langutil.regex_from_str("hi")
     assert read_str_first('#"\s"') == langutil.regex_from_str(r"\s")