Add support for NaN, positive infinity, and negative infinity literals (#582)

* Add support for NaN, positive infinity, and negative infinity literals

* Changelog

* Be less dumb

Author: chrisrink10

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
  * Added support for auto-resolving namespaces for keyword from the current namespace using the `::kw` syntax (#576)
  * Added support for namespaced map syntax (#577)
+ * Added support for numeric constant literals for NaN, positive infinity, and negative infinity (#582)
 
 ### Fixed
  * Fixed a bug where `def` forms did not permit recursive references to the `def`'ed Vars (#578)

src/basilisp/lang/obj.py

@@ -1,4 +1,5 @@
 import datetime
+import math
 import re
 import uuid
 from abc import ABC, abstractmethod
@@ -241,6 +242,15 @@ def _lrepr_complex(o: complex, **_) -> str:
     return repr(o).upper()
 
 
+@lrepr.register(float)
+def _lrepr_float(o: float, **_) -> str:
+    if math.isinf(o):
+        return "##Inf" if o > 0 else "##-Inf"
+    if math.isnan(o):
+        return "##NaN"
+    return repr(o)
+
+
 @lrepr.register(datetime.datetime)
 def _lrepr_datetime(o: datetime.datetime, **_) -> str:
     return f'#inst "{o.isoformat()}"'

src/basilisp/lang/reader.py

@@ -1229,6 +1229,25 @@ def _read_regex(ctx: ReaderContext) -> Pattern:
         raise ctx.syntax_error(f"Unrecognized regex pattern syntax: {s}")
 
 
+_NUMERIC_CONSTANTS = {
+    "NaN": float("nan"),
+    "Inf": float("inf"),
+    "-Inf": -float("inf"),
+}
+
+
+def _read_numeric_constant(ctx: ReaderContext) -> float:
+    start = ctx.reader.advance()
+    assert start == "#"
+    ns, name = _read_namespaced(ctx)
+    if ns is not None:
+        raise ctx.syntax_error(f"Unrecognized numeric constant: '##{ns}/{name}'")
+    c = _NUMERIC_CONSTANTS.get(name)
+    if c is None:
+        raise ctx.syntax_error(f"Unrecognized numeric constant: '##{name}'")
+    return c
+
+
 def _should_splice_reader_conditional(ctx: ReaderContext, form: LispReaderForm) -> bool:
     """Return True if and only if form is a ReaderConditional which should be spliced
     into a surrounding collection context."""
@@ -1357,6 +1376,8 @@ def _read_reader_macro(ctx: ReaderContext) -> LispReaderForm:
         return _read_comment(ctx)
     elif token == "?":
         return _read_reader_conditional(ctx)
+    elif token == "#":
+        return _read_numeric_constant(ctx)
     elif ns_name_chars.match(token):
         s = _read_sym(ctx)
         assert isinstance(s, symbol.Symbol)

tests/basilisp/lrepr_test.py

@@ -1,3 +1,4 @@
+import math
 import re
 import uuid
 from fractions import Fraction
@@ -198,6 +199,9 @@ def test_lrepr(lcompile: CompileFn):
     assert "0.64" == lcompile("(pr-str 0.64)")
     assert "3.14" == lcompile("(pr-str 3.14M)")
     assert "22/7" == lcompile("(pr-str 22/7)")
+    assert "##NaN" == lcompile("(pr-str ##NaN)")
+    assert "##Inf" == lcompile("(pr-str ##Inf)")
+    assert "##-Inf" == lcompile("(pr-str ##-Inf)")
     assert '"hi"' == lcompile('(pr-str "hi")')
     assert '"Hello\\nworld!"' == lcompile('(pr-str "Hello\nworld!")')
     assert '#uuid "81f35603-0408-4b3d-bbc0-462e3702747f"' == lcompile(
@@ -231,6 +235,9 @@ def test_lrepr_round_trip(lcompile: CompileFn):
     assert 0.64 == lcompile("(read-string (pr-str 0.64))")
     assert 3.14 == lcompile("(read-string (pr-str 3.14M))")
     assert Fraction(22, 7) == lcompile("(read-string (pr-str 22/7))")
+    assert math.isnan(lcompile("(read-string (pr-str ##NaN))"))
+    assert float("inf") == lcompile("(read-string (pr-str ##Inf))")
+    assert -float("inf") == lcompile("(read-string (pr-str ##-Inf))")
     assert "hi" == lcompile('(read-string (pr-str "hi"))')
     assert "Hello\nworld!" == lcompile('(read-string (pr-str "Hello\nworld!"))')
     assert uuid.UUID("81f35603-0408-4b3d-bbc0-462e3702747f") == lcompile(
@@ -271,6 +278,9 @@ def test_lstr(lcompile: CompileFn):
     assert "0.64" == lcompile("(print-str 0.64)")
     assert "3.14" == lcompile("(print-str 3.14M)")
     assert "22/7" == lcompile("(print-str 22/7)")
+    assert "##NaN" == lcompile("(print-str ##NaN)")
+    assert "##Inf" == lcompile("(print-str ##Inf)")
+    assert "##-Inf" == lcompile("(print-str ##-Inf)")
     assert "hi" == lcompile('(print-str "hi")')
     assert "Hello\nworld!" == lcompile('(print-str "Hello\nworld!")')
     assert '#uuid "81f35603-0408-4b3d-bbc0-462e3702747f"' == lcompile(

tests/basilisp/reader_test.py

@@ -1,4 +1,5 @@
 import io
+import math
 from typing import Optional
 
 import pytest
@@ -1265,6 +1266,18 @@ def test_regex_reader_literal():
         read_str_first(r'#"\y"')
 
 
+def test_numeric_constant_literal():
+    assert math.isnan(read_str_first("##NaN"))
+    assert read_str_first("##Inf") == float("inf")
+    assert read_str_first("##-Inf") == -float("inf")
+
+    with pytest.raises(reader.SyntaxError):
+        read_str_first("##float/NaN")
+
+    with pytest.raises(reader.SyntaxError):
+        read_str_first("##e")
+
+
 def test_uuid_reader_literal():
     assert read_str_first(
         '#uuid "4ba98ef0-0620-4966-af61-f0f6c2dbf230"'