From 8c7ff22c9cce5478eb20046b7f5f649f529cdf95 Mon Sep 17 00:00:00 2001
From: mryouse
Date: Fri, 29 Jul 2022 19:35:26 +0000
Subject: implement a :nil type, which is the empty list

---
 neb/std/types.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'neb/std/types.py')

diff --git a/neb/std/types.py b/neb/std/types.py
index 44906d8..20aa27a 100644
--- a/neb/std/types.py
+++ b/neb/std/types.py
@@ -174,12 +174,21 @@ istype_multi = MultiFunction("type?")
 istype_multi.register(istype_func)
 TYPES.register("type?", istype_multi)
 
+def interpretIsNil(symbol, args, env, ns):
+    return Bool(isinstance(args[0], List) and len(args[0].args) == 0)
+
+isnil_func = Builtin("nil?", interpretIsNil, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool"))
+isnil_multi = MultiFunction("nil?")
+isnil_multi.register(isnil_func)
+TYPES.register("nil?", isnil_multi)
+
 # add types to env
 any_type = NebType(":any", None, interpretIsAny)
 literal_type = NebType(":literal", any_type, interpretIsLiteral)
 string_type = NebType(":string", literal_type, interpretIsString)
 #list_type = NebType(":list", any_type, interpretIsList)
 bracket_type = NebType(":[]", any_type, interpretIsList)
+nil_type = NebType(":nil", bracket_type, interpretIsNil)
 brace_type = NebType(":{}", any_type, interpretIsNonEmptyList)
 bool_type = NebType(":bool", literal_type, interpretIsBool)
 number_type = NebType(":number", literal_type, interpretIsNumber)
@@ -193,6 +202,7 @@ TYPES.register(":literal", literal_type)
 TYPES.register(":string", string_type)
 #TYPES.register(":list", list_type)
 TYPES.register(":[]", bracket_type)
+TYPES.register(":nil", nil_type)
 TYPES.register(":{}", brace_type)
 TYPES.register(":bool", bool_type)
 TYPES.register(":number", number_type)
-- 
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