Hy reader macros #377

Added first iteration of reader macros
Refactored defmacro and defreader
Added test inn hy/tests/lex/test_lex.py
Added new test in hy/tests/native/tests
Added new test in hy/tests/macros.

changed the error given in the dispatch macro and added some handling for missing symbol and invalid characters

hy/compiler.py

@@ -36,6 +36,7 @@ from hy.models.float import HyFloat
 from hy.models.list import HyList
 from hy.models.dict import HyDict
 
+import hy.macros
 from hy.macros import require, macroexpand
 from hy._compat import str_type, long_type
 import hy.importer
@@ -1753,6 +1754,19 @@ class HyASTCompiler(object):
             bases=bases_expr,
             body=body.stmts)
 
+    def _compile_time_hack(self, expression):
+        """Compile-time hack: we want to get our new macro now
+        We must provide __name__ in the namespace to make the Python
+        compiler set the __module__ attribute of the macro function."""
+        hy.importer.hy_eval(expression,
+                            compile_time_ns(self.module_name),
+                            self.module_name)
+
+        # We really want to have a `hy` import to get hy.macro in
+        ret = self.compile(expression)
+        ret.add_imports('hy', [None])
+        return ret
+
     @builds("defmacro")
     @checkargs(min=1)
     def compile_macro(self, expression):
@@ -1768,16 +1782,30 @@ class HyASTCompiler(object):
             HyExpression([HySymbol("fn")] + expression),
         ]).replace(expression)
 
-        # Compile-time hack: we want to get our new macro now
-        # We must provide __name__ in the namespace to make the Python
-        # compiler set the __module__ attribute of the macro function.
-        hy.importer.hy_eval(new_expression,
-                            compile_time_ns(self.module_name),
-                            self.module_name)
+        ret = self._compile_time_hack(new_expression)
 
-        # We really want to have a `hy` import to get hy.macro in
-        ret = self.compile(new_expression)
-        ret.add_imports('hy', [None])
+        return ret
+
+    @builds("defreader")
+    @checkargs(min=2, max=3)
+    def compile_reader(self, expression):
+        expression.pop(0)
+        name = expression.pop(0)
+        NOT_READERS = [":", "&"]
+        if name in NOT_READERS:
+            raise NameError("%s can't be used as a macro reader symbol" % name)
+        if not isinstance(name, HySymbol):
+            raise HyTypeError(name,
+                              ("received a `%s' instead of a symbol "
+                               "for reader macro name" % type(name).__name__))
+        name = HyString(name).replace(name)
+        new_expression = HyExpression([
+            HySymbol("with_decorator"),
+            HyExpression([HySymbol("hy.macros.reader"), name]),
+            HyExpression([HySymbol("fn")] + expression),
+        ]).replace(expression)
+
+        ret = self._compile_time_hack(new_expression)
 
         return ret
 

hy/core/macros.hy

@@ -25,7 +25,6 @@
 ;;; These macros form the hy language
 ;;; They are automatically required in every module, except inside hy.core
 
-
 (defmacro for [args &rest body]
   "shorthand for nested foreach loops:
   (for [x foo y bar] baz) ->
@@ -144,3 +143,13 @@
       (setv -args (cdr (car -args))))
 
     `(apply ~-fun [~@-args] (dict (sum ~-okwargs [])))))
+
+
+(defmacro dispatch-reader-macro [char &rest body]
+  "Dispatch a reader macro based on the character"
+  (import [hy.macros])
+  (setv str_char (get char 1))
+  (if (not (in str_char hy.macros._hy_reader_chars))
+    (raise (hy.compiler.HyTypeError char (.format "There is no reader macro with the character `{0}`" str_char))))
+  `(do (import [hy.macros [_hy_reader]])
+       ((get (get _hy_reader --name--) ~char) ~(get body 0))))

hy/lex/lexer.py

@@ -40,6 +40,7 @@ lg.add('QUASIQUOTE', r'`%s' % end_quote)
 lg.add('UNQUOTESPLICE', r'~@%s' % end_quote)
 lg.add('UNQUOTE', r'~%s' % end_quote)
 lg.add('HASHBANG', r'#!.*[^\r\n]')
+lg.add('HASHREADER', r'#.')
 
 
 lg.add('STRING', r'''(?x)

hy/lex/parser.py

@@ -150,6 +150,15 @@ def term_unquote_splice(p):
     return HyExpression([HySymbol("unquote_splice"), p[1]])
 
 
+@pg.production("term : HASHREADER term")
+@set_quote_boundaries
+def hash_reader(p):
+    st = p[0].getstr()[1]
+    str_object = HyExpression([HySymbol("quote"), HyString(st)])
+    expr = HyExpression([HySymbol("quote"), p[1]])
+    return HyExpression([HySymbol("dispatch_reader_macro"), str_object, expr])
+
+
 @pg.production("dict : LCURLY list_contents RCURLY")
 @set_boundaries
 def t_dict(p):

hy/macros.py

@@ -40,6 +40,8 @@ EXTRA_MACROS = [
 ]
 
 _hy_macros = defaultdict(dict)
+_hy_reader = defaultdict(dict)
+_hy_reader_chars = set()
 
 
 def macro(name):
@@ -63,6 +65,30 @@ def macro(name):
     return _
 
 
+def reader(name):
+    """Decorator to define a macro called `name`.
+
+    This stores the macro `name` in the namespace for the module where it is
+    defined.
+
+    If the module where it is defined is in `hy.core`, then the macro is stored
+    in the default `None` namespace.
+
+    This function is called from the `defmacro` special form in the compiler.
+
+    """
+    def _(fn):
+        module_name = fn.__module__
+        if module_name.startswith("hy.core"):
+            module_name = None
+        _hy_reader[module_name][name] = fn
+
+        # Ugly hack to get some error handling
+        _hy_reader_chars.add(name)
+        return fn
+    return _
+
+
 def require(source_module, target_module):
     """Load the macros from `source_module` in the namespace of
     `target_module`.
@@ -75,6 +101,11 @@ def require(source_module, target_module):
     for name, macro in macros.items():
         refs[name] = macro
 
+    readers = _hy_reader[source_module]
+    reader_refs = _hy_reader[target_module]
+    for name, reader in readers.items():
+        reader_refs[name] = reader
+
 
 # type -> wrapping function mapping for _wrap_value
 _wrappers = {

tests/__init__.py

@@ -11,3 +11,4 @@ from .native_tests.unless import *  # noqa
 from .native_tests.when import *  # noqa
 from .native_tests.with_decorator import *  # noqa
 from .native_tests.core import *  # noqa
+from .native_tests.reader_macros import *  # noqa

tests/lex/test_lex.py

@@ -252,3 +252,11 @@ def test_complex():
     assert entry == HyComplex("1.0j")
     entry = tokenize("(j)")[0][0]
     assert entry == HySymbol("j")
+
+
+def test_reader_macro():
+    """Ensure reader macros are handles properly"""
+    entry = tokenize("#^()")
+    assert entry[0][0] == HySymbol("dispatch_reader_macro")
+    assert entry[0][1] == HyExpression([HySymbol("quote"), HyString("^")])
+    assert len(entry[0]) == 3

tests/macros/test_reader_macros.py

@@ -0,0 +1,11 @@
+from hy.macros import macroexpand
+from hy.compiler import HyTypeError
+from hy.lex import tokenize
+
+
+def test_reader_macro_error():
+    """Check if we get correct error with wrong disptach character"""
+    try:
+        macroexpand(tokenize("(dispatch_reader_macro '- '())")[0], __name__)
+    except HyTypeError as e:
+        assert "with the character `-`" in str(e)

tests/native_tests/reader_macros.hy

@@ -0,0 +1,32 @@
+(defn test-reader-macro []
+  "Test a basic redaer macro"
+  (defreader ^ [expr]
+    expr)
+
+  (assert (= #^"works" "works")))
+
+
+(defn test-reader-macro-expr []
+  "Test basic exprs like lists and arrays"
+  (defreader n [expr]
+    (get expr 1))
+
+  (assert (= #n[1 2] 2))
+  (assert (= #n(1 2) 2)))
+
+
+(defn test-reader-macro-override []
+  "Test if we can override function symbols"
+  (defreader + [n]
+    (+ n 1))
+
+  (assert (= #+2 3)))
+
+
+(defn test-reader-macro-compile-docstring []
+  "Test if we can compile with a docstring"
+  (try
+    (defreader d []
+      "Compiles with docstrings")
+    (except [Exception] 
+            (assert False))))