add return types to builtins

11 files changed, 63 insertions, 64 deletions

diff --git a/neb/std/boolean.py b/neb/std/boolean.py
index 1d99737..973fa67 100644
--- a/neb/std/boolean.py
+++ b/neb/std/boolean.py
@@ -14,7 +14,7 @@ def interpretOr(symbol, args, env, ns):
     return Bool(False)
 
 or_arg = Arg("arg", TypeEnum.BOOL, lazy=True)
-BOOLEAN.register("or", Builtin("or", interpretOr, [or_arg, or_arg], or_arg))
+BOOLEAN.register("or", Builtin("or", interpretOr, [or_arg, or_arg], or_arg, Type(":bool")))
 
 def interpretAnd(symbol, args, env, ns):
     # and returns false for the first expression that returns false
@@ -26,7 +26,7 @@ def interpretAnd(symbol, args, env, ns):
             return ev
     return Bool(True)
 
-BOOLEAN.register("and", Builtin("and", interpretAnd, [or_arg, or_arg], or_arg))
+BOOLEAN.register("and", Builtin("and", interpretAnd, [or_arg, or_arg], or_arg, Type(":bool")))
 
 def interpretEq(symbol, args, env, ns):
     # NOTE this currently only works for literals
@@ -37,11 +37,11 @@ def interpretEq(symbol, args, env, ns):
         return Bool(False)
 
 eq_arg = Arg("value", TypeEnum.LITERAL)
-BOOLEAN.register("eq?", Builtin("eq?", interpretEq, [eq_arg, eq_arg]))
+BOOLEAN.register("eq?", Builtin("eq?", interpretEq, [eq_arg, eq_arg], return_type=Type(":bool")))
 
 
 def interpretNot(symbol, args, env, ns):
     return Bool(not args[0].value)
 
 not_arg = Arg("not", TypeEnum.BOOL)
-BOOLEAN.register("not", Builtin("not", interpretNot, [not_arg]))
+BOOLEAN.register("not", Builtin("not", interpretNot, [not_arg], return_type=Type(":bool")))
diff --git a/neb/std/core.py b/neb/std/core.py
index d9f512e..1c3c4b4 100644
--- a/neb/std/core.py
+++ b/neb/std/core.py
@@ -30,7 +30,7 @@ def interpretDef(symbol, args, env, ns):
 
 def_name_arg = Arg("name", TypeEnum.ANY, lazy=True)
 def_val_arg = Arg("value", TypeEnum.ANY)
-CORE.register("def", Builtin("def", interpretDef, [def_name_arg, def_val_arg]))
+CORE.register("def", Builtin("def", interpretDef, [def_name_arg, def_val_arg], return_type=Type(":list")))
 
 def interpretRedef(symbol, args, env, ns):
     if not isinstance(args[0], Symbol):
@@ -42,7 +42,7 @@ def interpretRedef(symbol, args, env, ns):
     env.reregister(name, args[1])
     return List([])
 
-CORE.register("redef", Builtin("redef", interpretRedef, [def_name_arg, def_val_arg]))
+CORE.register("redef", Builtin("redef", interpretRedef, [def_name_arg, def_val_arg], return_type=Type(":list")))
 
 def interpretLambda(symbol, args, env, ns):
     new_args = args
@@ -121,7 +121,7 @@ def interpretFunc(symbol, args, env, ns):
     env.register(name, func)
     return List([])
 
-CORE.register("func", Builtin("func", interpretFunc, [def_name_arg, lambda_args_arg, lambda_body_arg], lambda_body_arg))
+CORE.register("func", Builtin("func", interpretFunc, [def_name_arg, lambda_args_arg, lambda_body_arg], lambda_body_arg, Type(":list")))
 
 def interpretBlock(symbol, args, env, ns):
     ret = List([])
@@ -157,14 +157,14 @@ def interpretUse(symbol, args, env, ns):
     interpret(parse(lex(data)), env, ns)
     return List([])
 
-CORE.register("use", Builtin("use", interpretUse, [Arg("filename", TypeEnum.STRING)]))
+CORE.register("use", Builtin("use", interpretUse, [Arg("filename", TypeEnum.STRING)], return_type=Type(":list")))
 
 def interpretAssert(symbol, args, env, ns):
     if args[0].value != True:
         raise InterpretPanic(symbol, "assertion failed")
     return List([])
 
-CORE.register("assert", Builtin("assert", interpretAssert, [Arg("cond", TypeEnum.BOOL)]))
+CORE.register("assert", Builtin("assert", interpretAssert, [Arg("cond", TypeEnum.BOOL)], return_type=Type(":list")))
 
 def interpretUseAs(symbol, args, env, ns):
     target_file_name = args[0].value
@@ -176,7 +176,7 @@ def interpretUseAs(symbol, args, env, ns):
     interpret(parse(lex(data)), env, args[1].name)
     return List([])
 
-CORE.register("use-as", Builtin("use-as", interpretUseAs, [Arg("filename", TypeEnum.STRING), Arg("namespace", TypeEnum.ANY, lazy=True)]))
+CORE.register("use-as", Builtin("use-as", interpretUseAs, [Arg("filename", TypeEnum.STRING), Arg("namespace", TypeEnum.ANY, lazy=True)], return_type=Type(":list")))
 
 def interpretQuote(symbol, args, env, ns):
     return args[0]
@@ -218,4 +218,3 @@ type_parent_arg = Arg("name", TypeEnum.ANY)
 type_func_arg = Arg("func", TypeEnum.ANY)
 CORE.register("type", Builtin("type", interpretType, [type_name_arg, type_parent_arg, type_func_arg]))
 
-
diff --git a/neb/std/fs.py b/neb/std/fs.py
index 5983e20..495c7ea 100644
--- a/neb/std/fs.py
+++ b/neb/std/fs.py
@@ -8,13 +8,13 @@ FS = Environment()
 def interpretExists(symbol, args, env, ns):
     return Bool(Path(args[0].value).resolve().exists())
 
-FS.register("exists?", Builtin("exists?", interpretExists, [Arg("filename", TypeEnum.STRING)]))
+FS.register("exists?", Builtin("exists?", interpretExists, [Arg("filename", TypeEnum.STRING)], return_type=Type(":bool")))
 
 def interpretGlob(symbol, args, env, ns):
     items = glob(args[0].value)
     return List([String(item) for item in items])
 
-FS.register("glob", Builtin("glob", interpretGlob, [Arg("regex", TypeEnum.STRING)]))
+FS.register("glob", Builtin("glob", interpretGlob, [Arg("regex", TypeEnum.STRING)], return_type=Type(":string")))
 
 def interpretUnlink(symbol, args, env, ns):
     target_path = Path(args[0].value).resolve()
@@ -23,7 +23,7 @@ def interpretUnlink(symbol, args, env, ns):
     target_path.unlink()
     return List([])
 
-FS.register("unlink", Builtin("unlink", interpretUnlink, [Arg("filename", TypeEnum.STRING)]))
+FS.register("unlink", Builtin("unlink", interpretUnlink, [Arg("filename", TypeEnum.STRING)], return_type=Type(":list")))
 
 def interpretWithWrite(symbol, args, env, ns):
     target_file = args[0]
@@ -57,5 +57,5 @@ def interpretReadLines(symbol, args, env, ns):
     out = List([String(d) for d in data]) # all lines are strings
     return out
 
-FS.register("read-lines", Builtin("read-lines", interpretReadLines, [Arg("filename", TypeEnum.STRING)]))
+FS.register("read-lines", Builtin("read-lines", interpretReadLines, [Arg("filename", TypeEnum.STRING)], return_type=Type(":list")))
 
diff --git a/neb/std/functools.py b/neb/std/functools.py
index facc97d..9e426b8 100644
--- a/neb/std/functools.py
+++ b/neb/std/functools.py
@@ -17,7 +17,7 @@ def interpretFilter(symbol, args, env, ns):
             out.append(arg)
     return List(out)
 
-FUNCTOOLS.register("filter", Builtin("filter", interpretFilter, [Arg("func", TypeEnum.ANY), Arg("list", TypeEnum.LIST)]))
+FUNCTOOLS.register("filter", Builtin("filter", interpretFilter, [Arg("func", TypeEnum.ANY), Arg("list", TypeEnum.LIST)], return_type=Type(":list")))
 
 def interpretMap(symbol, args, env, ns):
     func = args[0]
@@ -32,7 +32,7 @@ def interpretMap(symbol, args, env, ns):
         out.append(ev)
     return List(out)
 
-FUNCTOOLS.register("map", Builtin("map", interpretMap, [Arg("func", TypeEnum.ANY), Arg("list", TypeEnum.LIST)]))
+FUNCTOOLS.register("map", Builtin("map", interpretMap, [Arg("func", TypeEnum.ANY), Arg("list", TypeEnum.LIST)], return_type=Type(":list")))
 
 def interpretApply(symbol, args, env, ns):
     # TODO: to support lambdas, we can't assume the func is defined
diff --git a/neb/std/lists.py b/neb/std/lists.py
index 5aaab53..1ecbb6d 100644
--- a/neb/std/lists.py
+++ b/neb/std/lists.py
@@ -7,7 +7,7 @@ LISTS = Environment()
 def interpretListLength(symbol, args, env, ns):
     return Int(len(args[0].args))
 
-LISTS.register("list-length", Builtin("list-length", interpretListLength, [Arg("arg", TypeEnum.LIST)]))
+LISTS.register("list-length", Builtin("list-length", interpretListLength, [Arg("arg", TypeEnum.LIST)], return_type=Type(":int")))
     
 def interpretFirst(symbol, args, env, ns):
     if len(args[0].args) == 0:
@@ -20,26 +20,26 @@ def interpretRest(symbol, args, env, ns):
     # TODO do we know it's not evaluated?
     return List(args[0].args[1:]) # we don't evaluate the remainder of the list
 
-LISTS.register("rest", Builtin("rest", interpretRest, [Arg("arg", TypeEnum.LIST)]))
+LISTS.register("rest", Builtin("rest", interpretRest, [Arg("arg", TypeEnum.LIST)], return_type=Type(":list")))
 
 def interpretListReverse(symbol, args, env, ns):
     new_args = args[0].args[:] # make a copy of the args
     new_args.reverse()
     return List(new_args)
 
-LISTS.register("list-reverse", Builtin("list-reverse", interpretListReverse, [Arg("list", TypeEnum.LIST)]))
+LISTS.register("list-reverse", Builtin("list-reverse", interpretListReverse, [Arg("list", TypeEnum.LIST)], return_type=Type(":list")))
 
 def interpretEmpty(symbol, args, env, ns):
     return Bool(len(args[0].args) == 0)
 
-LISTS.register("empty?", Builtin("empty?", interpretEmpty, [Arg("list", TypeEnum.LIST)]))
+LISTS.register("empty?", Builtin("empty?", interpretEmpty, [Arg("list", TypeEnum.LIST)], return_type=Type(":bool")))
 
 def interpretShuf(symbol, args, env, ns):
     items = args[0].args[:]
     random.shuffle(items)
     return List(items)
 
-LISTS.register("shuf", Builtin("shuf", interpretShuf, [Arg("list", TypeEnum.LIST)]))
+LISTS.register("shuf", Builtin("shuf", interpretShuf, [Arg("list", TypeEnum.LIST)], return_type=Type(":list")))
 
 def interpretIn(symbol, args, env, ns):
     target = args[0]
@@ -51,7 +51,7 @@ def interpretIn(symbol, args, env, ns):
 
 in_target_arg = Arg("target", TypeEnum.LITERAL)
 in_list_arg = Arg("list", TypeEnum.LIST)
-LISTS.register("in?", Builtin("in?", interpretIn, [in_target_arg, in_list_arg]))
+LISTS.register("in?", Builtin("in?", interpretIn, [in_target_arg, in_list_arg], return_type=Type(":bool")))
 
 def interpretLast(symbol, args, env, ns):
     if len(args[0].args) == 0:
@@ -72,7 +72,7 @@ def interpretSlice(symbol, args, env, ns):
 slice_list_arg = Arg("list", TypeEnum.LIST)
 slice_idx_arg = Arg("idx", TypeEnum.INT)
 slice_length_arg = Arg("length", TypeEnum.INT, optional=True)
-LISTS.register("slice", Builtin("slice", interpretSlice, [slice_list_arg, slice_idx_arg, slice_length_arg]))
+LISTS.register("slice", Builtin("slice", interpretSlice, [slice_list_arg, slice_idx_arg, slice_length_arg], return_type=Type(":list")))
 
 def interpretAppend(symbol, args, env, ns):
     lst = args[0]
@@ -80,7 +80,7 @@ def interpretAppend(symbol, args, env, ns):
     items = lst.args[:]
     return List(items + [val])
 
-LISTS.register("append", Builtin("append", interpretAppend, [Arg("list", TypeEnum.LIST), Arg("item", TypeEnum.ANY)]))
+LISTS.register("append", Builtin("append", interpretAppend, [Arg("list", TypeEnum.LIST), Arg("item", TypeEnum.ANY)], return_type=Type(":list")))
 
 # TODO: this is actually for records/structs/whatever they're called
 def interpretRemove(symbol, args, env, ns):
@@ -92,7 +92,7 @@ def interpretRemove(symbol, args, env, ns):
             out.append(arg)
     return List(out)
 
-LISTS.register("remove", Builtin("remove", interpretRemove, [Arg("list", TypeEnum.LIST), Arg("key", TypeEnum.ANY)]))
+LISTS.register("remove", Builtin("remove", interpretRemove, [Arg("list", TypeEnum.LIST), Arg("key", TypeEnum.ANY)], return_type=Type(":list")))
 
 def interpretZip(symbol, args, env, ns):
     z1 = args[0]
@@ -107,12 +107,12 @@ def interpretZip(symbol, args, env, ns):
     return List(out)
 
 zip_arg = Arg("list", TypeEnum.LIST)
-LISTS.register("zip", Builtin("zip", interpretZip, [zip_arg, zip_arg]))
+LISTS.register("zip", Builtin("zip", interpretZip, [zip_arg, zip_arg], return_type=Type(":list")))
 
 def interpretList(symbol, args, env, ns):
     return List(args)
 
-LISTS.register("list", Builtin("list", interpretList, [], Arg("item", TypeEnum.ANY)))
+LISTS.register("list", Builtin("list", interpretList, [], Arg("item", TypeEnum.ANY), Type(":list")))
 
 def interpretSortNumbers(symbol, args, env, ns):
     items = []
@@ -129,4 +129,4 @@ def interpretSortNumbers(symbol, args, env, ns):
             out.append(Float(item))
     return List(out)
 
-LISTS.register("sort-numbers", Builtin("sort-numbers", interpretSortNumbers, [Arg("list", TypeEnum.LIST)]))
+LISTS.register("sort-numbers", Builtin("sort-numbers", interpretSortNumbers, [Arg("list", TypeEnum.LIST)], return_type=Type(":list")))
diff --git a/neb/std/math.py b/neb/std/math.py
index 66d153e..79ef332 100644
--- a/neb/std/math.py
+++ b/neb/std/math.py
@@ -8,23 +8,23 @@ def interpretLessThanEqual(symbol, args, env, ns):
     return Bool(args[0].value <= args[1].value)
 
 compare_arg = Arg("num", TypeEnum.NUMBER)
-MATH.register("<=", Builtin("<=", interpretLessThanEqual, [compare_arg, compare_arg]))
+MATH.register("<=", Builtin("<=", interpretLessThanEqual, [compare_arg, compare_arg], return_type=Type(":bool")))
 
 def interpretGreaterThan(symbol, args, env, ns):
     return Bool(args[0].value > args[1].value)
 
 compare_arg = Arg("num", TypeEnum.NUMBER)
-MATH.register(">", Builtin(">", interpretGreaterThan, [compare_arg, compare_arg]))
+MATH.register(">", Builtin(">", interpretGreaterThan, [compare_arg, compare_arg], return_type=Type(":bool")))
 
 def interpretGreaterThanEqual(symbol, args, env, ns):
     return Bool(args[0].value >= args[1].value)
 
-MATH.register(">=", Builtin(">=", interpretGreaterThanEqual, [compare_arg, compare_arg]))
+MATH.register(">=", Builtin(">=", interpretGreaterThanEqual, [compare_arg, compare_arg], return_type=Type(":bool")))
 
 def interpretLessThan(symbol, args, env, ns):
     return Bool(args[0].value < args[1].value)
 
-MATH.register("<", Builtin("<", interpretLessThan, [compare_arg, compare_arg]))
+MATH.register("<", Builtin("<", interpretLessThan, [compare_arg, compare_arg], return_type=Type(":bool")))
 
 def interpretAddition(symbol, args, env, ns):
     res = 0
@@ -36,7 +36,7 @@ def interpretAddition(symbol, args, env, ns):
         return Int(res)
 
 term_arg = Arg("term", TypeEnum.NUMBER)
-MATH.register("+", Builtin("+", interpretAddition, [term_arg], term_arg))
+MATH.register("+", Builtin("+", interpretAddition, [term_arg], term_arg, Type(":number")))
 
 def interpretSubtraction(symbol, args, env, ns):
     if len(args) == 1:
@@ -50,7 +50,7 @@ def interpretSubtraction(symbol, args, env, ns):
     else:
         return Int(res)
 
-MATH.register("-", Builtin("-", interpretSubtraction, [term_arg], term_arg))
+MATH.register("-", Builtin("-", interpretSubtraction, [term_arg], term_arg, Type(":number")))
 
 def interpretMultiplication(symbol, args, env, ns):
     res = args[0].value
@@ -62,7 +62,7 @@ def interpretMultiplication(symbol, args, env, ns):
         return Int(res)
 
 factor_arg = Arg("factor", TypeEnum.NUMBER)
-MATH.register("*", Builtin("*", interpretMultiplication, [factor_arg, factor_arg], factor_arg))
+MATH.register("*", Builtin("*", interpretMultiplication, [factor_arg, factor_arg], factor_arg, Type(":number")))
 
 def interpretDivision(symbol, args, env, ns):
     ret = args[0].value / args[1].value
@@ -71,9 +71,9 @@ def interpretDivision(symbol, args, env, ns):
     else:
         return Float(ret)
 
-MATH.register("/", Builtin("/", interpretDivision, [factor_arg, factor_arg]))
+MATH.register("/", Builtin("/", interpretDivision, [factor_arg, factor_arg], return_type=Type(":number")))
 
 def interpretFloor(symbol, args, env, ns):
     return Int(math.floor(args[0].value))
 
-MATH.register("floor", Builtin("floor", interpretFloor, [Arg("floor", TypeEnum.NUMBER)]))
+MATH.register("floor", Builtin("floor", interpretFloor, [Arg("floor", TypeEnum.NUMBER)], return_type=Type(":int")))
diff --git a/neb/std/repl.py b/neb/std/repl.py
index 39aba3b..43b514e 100644
--- a/neb/std/repl.py
+++ b/neb/std/repl.py
@@ -9,16 +9,16 @@ def interpretHowTo(symbol, args, env, ns):
     print(args[0].describe())
     return List([])
 
-REPL.register("howto", Builtin("howto", interpretHowTo, [Arg("symbol", TypeEnum.ANY)]))
+REPL.register("howto", Builtin("howto", interpretHowTo, [Arg("symbol", TypeEnum.ANY)], return_type=Type(":list")))
 
 def interpretSymbols(symbol, args, env, ns):
     keys = [Symbol(k, -1) for k,v in env.environment.items()]
     return List(keys)
 
-REPL.register("symbols", Builtin("symbols", interpretSymbols, []))
+REPL.register("symbols", Builtin("symbols", interpretSymbols, [], return_type=Type(":list")))
 
 def interpretUserSymbols(symbol, args, env, ns):
     keys = [Symbol(k, -1) for k,v in env.environment.items() if isinstance(v, UserFunction) or isinstance(v, Literal)]
     return List(keys)
 
-REPL.register("user-symbols", Builtin("user-symbols", interpretUserSymbols, []))
+REPL.register("user-symbols", Builtin("user-symbols", interpretUserSymbols, [], return_type=Type(":list")))
diff --git a/neb/std/strings.py b/neb/std/strings.py
index 68f02d5..7e3177e 100644
--- a/neb/std/strings.py
+++ b/neb/std/strings.py
@@ -10,12 +10,12 @@ def interpretConcat(symbol, args, env, ns):
     return String(out)
 
 string_arg = Arg("arg", TypeEnum.STRING)
-STRINGS.register("concat", Builtin("concat", interpretConcat, [string_arg, string_arg], string_arg))
+STRINGS.register("concat", Builtin("concat", interpretConcat, [string_arg, string_arg], string_arg, Type(":string")))
 
 def interpretStrip(symbol, args, env, ns):
     return String(args[0].value.strip())
 
-STRINGS.register("strip", Builtin("strip", interpretStrip, [Arg("filename", TypeEnum.STRING)]))
+STRINGS.register("strip", Builtin("strip", interpretStrip, [Arg("filename", TypeEnum.STRING)], return_type=Type(":string")))
 
 def interpretSplit(symbol, args, env, ns):
     target = args[0]
@@ -25,7 +25,7 @@ def interpretSplit(symbol, args, env, ns):
     ret = target.value.split(splitter.value)
     return List([String(r) for r in ret])
 
-STRINGS.register("split", Builtin("split", interpretSplit, [Arg("target", TypeEnum.STRING)], Arg("splitter", TypeEnum.STRING, optional=True)))
+STRINGS.register("split", Builtin("split", interpretSplit, [Arg("target", TypeEnum.STRING)], Arg("splitter", TypeEnum.STRING, optional=True), Type(":list")))
 
 def interpretJoin(symbol, args, env, ns):
     lst = args[0]
@@ -34,16 +34,16 @@ def interpretJoin(symbol, args, env, ns):
 
 join_list_arg = Arg("list", TypeEnum.LIST)
 join_string_arg = Arg("joiner", TypeEnum.STRING)
-STRINGS.register("join", Builtin("join", interpretJoin, [join_list_arg, join_string_arg]))
+STRINGS.register("join", Builtin("join", interpretJoin, [join_list_arg, join_string_arg], return_type=Type(":string")))
 
 def interpretFirstChar(symbol, args, env, ns):
     if len(args[0].value) == 0:
         raise InterpretPanic(symbol, ":string is empty", ev)
     return String(args[0].value[0])
 
-STRINGS.register("first-char", Builtin("first-char", interpretFirstChar, [Arg("string", TypeEnum.STRING)]))
+STRINGS.register("first-char", Builtin("first-char", interpretFirstChar, [Arg("string", TypeEnum.STRING)], return_type=Type(":string")))
 
 def interpretRestChar(symbol, args, env, ns):
     return String(args[0].value[1:])
 
-STRINGS.register("rest-char", Builtin("rest-char", interpretRestChar, [Arg("string", TypeEnum.STRING)]))
+STRINGS.register("rest-char", Builtin("rest-char", interpretRestChar, [Arg("string", TypeEnum.STRING)], return_type=Type(":string")))
diff --git a/neb/std/sys.py b/neb/std/sys.py
index 98266f2..61e83c2 100644
--- a/neb/std/sys.py
+++ b/neb/std/sys.py
@@ -12,13 +12,13 @@ def interpretArgv(symbol, args, env, ns):
         out.append(String(arg))
     return List(out)
 
-SYS.register("argv", Builtin("argv", interpretArgv, []))
+SYS.register("argv", Builtin("argv", interpretArgv, [], return_type=Type(":list")))
 
 def interpretShell(symbol, args, env, ns):
     ret = subprocess.run(shlex.split(args[0].value), capture_output=True)
     return List([String(r) for r in ret.stdout.decode("utf-8").split("\n")])
 
-SYS.register("$", Builtin("$", interpretShell, [Arg("command", TypeEnum.STRING)]))
+SYS.register("$", Builtin("$", interpretShell, [Arg("command", TypeEnum.STRING)], return_type=Type(":list")))
 
 def interpretExit(symbol, args, env, ns):
     status = 0 if len(args) == 0 else args[0].value
@@ -26,10 +26,10 @@ def interpretExit(symbol, args, env, ns):
     return List([])
 
 exit_arg = Arg("status", TypeEnum.INT, optional=True)
-SYS.register("exit", Builtin("exit", interpretExit, [exit_arg]))
+SYS.register("exit", Builtin("exit", interpretExit, [exit_arg], return_type=Type(":list")))
 
 def interpretPrint(symbol, args, env, ns):
     print(args[0].value)
     return List([])  # print returns nothing
 
-SYS.register("print", Builtin("print", interpretPrint, [Arg("arg", TypeEnum.STRING)]))
+SYS.register("print", Builtin("print", interpretPrint, [Arg("arg", TypeEnum.STRING)], return_type=Type(":list")))
diff --git a/neb/std/term.py b/neb/std/term.py
index 59f6fdf..e028b00 100644
--- a/neb/std/term.py
+++ b/neb/std/term.py
@@ -9,13 +9,13 @@ def interpretClear(symbol, args, env, ns):
     subprocess.run(["clear"])
     return List([])
 
-TERM.register("clear", Builtin("clear", interpretClear, []))
+TERM.register("clear", Builtin("clear", interpretClear, [], return_type=Type(":list")))
 
 def interpretReadLine(symbol, args, env, ns):
     ret = input(args[0].value)
     return String(ret)
 
-TERM.register("read-line", Builtin("read-line", interpretReadLine, [Arg("prompt", TypeEnum.STRING)]))
+TERM.register("read-line", Builtin("read-line", interpretReadLine, [Arg("prompt", TypeEnum.STRING)], return_type=Type(":string")))
 
 def interpretReadChar(symbol, args, env, ns):
     import termios, tty
@@ -30,4 +30,4 @@ def interpretReadChar(symbol, args, env, ns):
         termios.tcsetattr(fd, termios.TCSADRAIN, old)
     return String(ch.decode("utf-8"))
 
-TERM.register("read-char", Builtin("read-char", interpretReadChar, []))
+TERM.register("read-char", Builtin("read-char", interpretReadChar, [], return_type=Type(":string")))
diff --git a/neb/std/types.py b/neb/std/types.py
index b5fb993..f8d5405 100644
--- a/neb/std/types.py
+++ b/neb/std/types.py
@@ -6,33 +6,33 @@ TYPES = Environment()
 def interpretIsBool(symbol, args, env, ns):
     return Bool(isinstance(args[0], Bool))
 
-TYPES.register("bool?", Builtin("bool?", interpretIsBool, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("bool?", Builtin("bool?", interpretIsBool, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsFloat(symbol, args, env, ns):
     return Bool(isinstance(args[0], Float))
 
-TYPES.register("float?", Builtin("float?", interpretIsFloat, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("float?", Builtin("float?", interpretIsFloat, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsNumber(symbol, args, env, ns):
     ret = isinstance(args[0], Int) or isinstance(args[0], Float)
     return Bool(ret)
 
-TYPES.register("number?", Builtin("number?", interpretIsNumber, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("number?", Builtin("number?", interpretIsNumber, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsInt(symbol, args, env, ns):
     return Bool(isinstance(args[0], Int))
 
-TYPES.register("int?", Builtin("int?", interpretIsInt, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("int?", Builtin("int?", interpretIsInt, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsList(symbol, args, env, ns):
     return Bool(isinstance(args[0], List))
 
-TYPES.register("list?", Builtin("list?", interpretIsList, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("list?", Builtin("list?", interpretIsList, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsString(symbol, args, env, ns):
     return Bool(isinstance(args[0], String))
 
-TYPES.register("string?", Builtin("string?", interpretIsString, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("string?", Builtin("string?", interpretIsString, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretStringToInt(symbol, args, env, ns):
     try:
@@ -41,7 +41,7 @@ def interpretStringToInt(symbol, args, env, ns):
     except:
         raise InterpretPanic(symbol, "can't convert to an :int", args[0])
 
-TYPES.register("string->int", Builtin("string->int", interpretStringToInt, [Arg("arg", TypeEnum.STRING)]))
+TYPES.register("string->int", Builtin("string->int", interpretStringToInt, [Arg("arg", TypeEnum.STRING)], return_type=Type(":int")))
 
 def interpretToString(symbol, args, env, ns):
     item = args[0]
@@ -52,7 +52,7 @@ def interpretToString(symbol, args, env, ns):
     else:
         return String(f"{item}")
 
-TYPES.register("->string", Builtin("->string", interpretToString, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("->string", Builtin("->string", interpretToString, [Arg("arg", TypeEnum.ANY)], return_type=Type(":string")))
 
 def interpretTypeOf(symbol, args, env, ns):
     return Type(f"{args[0].type_}")
@@ -62,12 +62,12 @@ TYPES.register("typeof", Builtin("typeof", interpretTypeOf, [Arg("candidate", Ty
 def interpretIsAny(symbol, args, env, ns):
     return Bool(True)
 
-TYPES.register("any?", Builtin("any?", interpretIsAny, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("any?", Builtin("any?", interpretIsAny, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 def interpretIsLiteral(symbol, args, env, ns):
     return Bool(isinstance(args[0], Literal))
 
-TYPES.register("literal?", Builtin("literal?", interpretIsLiteral, [Arg("arg", TypeEnum.ANY)]))
+TYPES.register("literal?", Builtin("literal?", interpretIsLiteral, [Arg("arg", TypeEnum.ANY)], return_type=Type(":bool")))
 
 # add types to env
 any_type = NebType(":any", None, interpretIsAny)