Add tagged-literal support (#1101)

Fixes #1104 

This is a first draft at getting tagged literals working. I don't have
much experience with python, so I may have made some amateur mistakes.

---------

Co-authored-by: Chris Rink <chrisrink10@users.noreply.github.com>

Author: djblue

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
  * Added support for the `:param-tags` reader metadata syntax `^[tag ...]` from Clojure 1.12 (#1111)
+ * Add support for tagged literals (#1104)
 
 ### Changed
  * Types generated by `reify` may optionally be marked as `^:mutable` now to prevent `attrs.exceptions.FrozenInstanceError`s being thrown when mutating methods inherited from the supertype(s) are called (#1088)

src/basilisp/core.lpy

@@ -547,6 +547,17 @@
     v
     (.-name v)))
 
+(defn ^:inline tagged-literal
+  "Construct a data representation of a tagged literal from a
+  tag symbol and a form."
+  [tag form]
+  (basilisp.lang.tagged/tagged-literal tag form))
+
+(defn ^:inline tagged-literal?
+  "Return true if the value is the data representation of a tagged literal"
+  [o]
+  (instance? basilisp.lang.tagged/TaggedLiteral o))
+
 (defn ^:inline namespace
   "Return the namespace of a symbol or keyword, or ``nil`` if no namespace."
   [v]

src/basilisp/lang/compiler/generator.py

@@ -698,6 +698,7 @@ def _var_ns_as_python_sym(name: str) -> str:
 _SEQ_ALIAS = genname("seq")
 _SET_ALIAS = genname("lset")
 _SYM_ALIAS = genname("sym")
+_TAGGED_ALIAS = genname("tagged")
 _VEC_ALIAS = genname("vec")
 _VOLATILE_ALIAS = genname("volatile")
 _VAR_ALIAS = genname("Var")
@@ -731,6 +732,7 @@ def _var_ns_as_python_sym(name: str) -> str:
     "basilisp.lang.seq": _SEQ_ALIAS,
     "basilisp.lang.set": _SET_ALIAS,
     "basilisp.lang.symbol": _SYM_ALIAS,
+    "basilisp.lang.tagged": _TAGGED_ALIAS,
     "basilisp.lang.vector": _VEC_ALIAS,
     "basilisp.lang.volatile": _VOLATILE_ALIAS,
     "basilisp.lang.util": _UTIL_ALIAS,

src/basilisp/lang/runtime.py

@@ -551,6 +551,7 @@ class Namespace(ReferenceBase):
                 "basilisp.lang.seq",
                 "basilisp.lang.set",
                 "basilisp.lang.symbol",
+                "basilisp.lang.tagged",
                 "basilisp.lang.vector",
                 "basilisp.lang.volatile",
                 "basilisp.lang.util",

src/basilisp/lang/tagged.py

@@ -0,0 +1,74 @@
+from typing import Optional, TypeVar, Union
+
+from typing_extensions import Unpack
+
+from basilisp.lang.interfaces import ILispObject, ILookup
+from basilisp.lang.keyword import keyword
+from basilisp.lang.obj import PrintSettings, lrepr
+from basilisp.lang.symbol import Symbol
+
+K = TypeVar("K")
+V = TypeVar("V")
+T = Union[None, V, Symbol]
+
+_TAG_KW = keyword("tag")
+_FORM_KW = keyword("form")
+
+
+class TaggedLiteral(
+    ILispObject,
+    ILookup[K, T],
+):
+    """Basilisp TaggedLiteral. https://clojure.org/reference/reader#tagged_literals"""
+
+    __slots__ = ("_tag", "_form", "_hash")
+
+    def __init__(self, tag: Symbol, form) -> None:
+        self._tag = tag
+        self._form = form
+        self._hash: Optional[int] = None
+
+    @property
+    def tag(self) -> Symbol:
+        return self._tag
+
+    @property
+    def form(self):
+        return self._form
+
+    def __bool__(self):
+        return True
+
+    def __eq__(self, other):
+        if self is other:
+            return True
+        if not isinstance(other, TaggedLiteral):
+            return NotImplemented
+        return self._tag == other._tag and self._form == other._form
+
+    def __hash__(self):
+        if self._hash is None:
+            self._hash = hash((self._tag, self._form))
+        return self._hash
+
+    def __getitem__(self, item):
+        return self.val_at(item)
+
+    def val_at(self, k: K, default: Optional[V] = None) -> T:
+        if k == _TAG_KW:
+            return self._tag
+        elif k == _FORM_KW:
+            return self._form
+        else:
+            return default
+
+    def _lrepr(self, **kwargs: Unpack[PrintSettings]) -> str:
+        return f"#{self._tag} {lrepr(self._form, **kwargs)}"
+
+
+def tagged_literal(tag: Symbol, form):
+    """Construct a data representation of a tagged literal from a
+    tag symbol and a form."""
+    if not isinstance(tag, Symbol):
+        raise TypeError(f"tag must be a Symbol, not '{type(tag)}'")
+    return TaggedLiteral(tag, form)

tests/basilisp/tagged_test.py

@@ -0,0 +1,18 @@
+from basilisp.lang.symbol import symbol
+from basilisp.lang.tagged import tagged_literal
+
+
+def test_tagged_literal():
+    tag = symbol("tag")
+    form = 1
+    tagged = tagged_literal(tag, form)
+    assert tagged.tag == tag
+    assert tagged.form == form
+
+
+def test_tagged_literal_str_and_repr():
+    tag = symbol("tag")
+    form = 1
+    tagged = tagged_literal(tag, form)
+    assert str(tagged) == "#tag 1"
+    assert repr(tagged) == "#tag 1"

tests/basilisp/test_tagged.lpy

@@ -0,0 +1,33 @@
+(ns tests.basilisp.test-tagged
+  (:require
+   [basilisp.test :refer [deftest is testing]]))
+
+(deftest tagged-literal-test
+  (let [tag 'tag
+        form 1
+        tagged (tagged-literal tag form)]
+    (testing "equality"
+      (is (= tagged tagged))
+      (is (= tagged (tagged-literal tag form)))
+      (is (not= tagged (tagged-literal 'foo form)))
+      (is (not= tagged (tagged-literal tag 2))))
+
+    (testing "accessors"
+      (is (= tag (:tag tagged)))
+      (is (= form (:form tagged)))
+      (is (nil? (:key tagged)))
+      (is (= ::default (:key tagged ::default))))
+
+    (testing "predicate"
+      (is (true? (tagged-literal? tagged)))
+      (is (false? (tagged-literal? nil)))
+      (is (false? (tagged-literal? 0)))
+      (is (false? (tagged-literal? ::foo))))
+
+    (testing "printing"
+      (is (= "#tag 1" (pr-str tagged)))
+      (is (= "#js []" (pr-str (tagged-literal 'js []))))
+      (is (= "#js {}" (pr-str (tagged-literal 'js {})))))
+
+    (testing "validation"
+      (is (thrown? TypeError (tagged-literal 1 1))))))