func does not exist test

src/ytdl_sub/script/types/function.py

@@ -23,6 +23,7 @@ from ytdl_sub.script.types.variable import FunctionArgument
 from ytdl_sub.script.types.variable import Variable
 from ytdl_sub.script.types.variable_dependency import VariableDependency
 from ytdl_sub.script.utils.exception_formatters import FunctionArgumentsExceptionFormatter
+from ytdl_sub.script.utils.exceptions import FunctionDoesNotExist
 from ytdl_sub.script.utils.exceptions import FunctionRuntimeException
 from ytdl_sub.script.utils.exceptions import UserThrownRuntimeError
 from ytdl_sub.script.utils.type_checking import FunctionInputSpec
@@ -101,7 +102,9 @@ class CustomFunction(Function):
                 custom_functions=custom_functions,
             )
 
-        raise StringFormattingException(f"Custom function {self.name} does not exist")
+        raise FunctionDoesNotExist(
+            f"Function %{self.name} does not exist as a built-in or custom function."
+        )
 
 
 class BuiltInFunction(Function, TypeHintedFunctionType):

src/ytdl_sub/script/types/lambda.py

@@ -0,0 +1,5 @@
+from ytdl_sub.script.types.resolvable import ArgumentType
+
+
+class Lambda(ArgumentType):
+    function_name: str

src/ytdl_sub/script/utils/exceptions.py

@@ -15,6 +15,10 @@ class IncompatibleFunctionArguments(UserException):
     """Function has invalid arguments"""
 
 
+class FunctionDoesNotExist(UserException):
+    """Tried to use a function that does not exist"""
+
+
 class FunctionRuntimeException(ValueError):
     """Exception thrown when a ytdl-sub function has an error occur at runtime"""
 

tests/unit/script/types/test_function.py

@@ -5,6 +5,7 @@ import pytest
 from ytdl_sub.script.script import Script
 from ytdl_sub.script.types.resolvable import Boolean
 from ytdl_sub.script.types.resolvable import String
+from ytdl_sub.script.utils.exceptions import FunctionDoesNotExist
 from ytdl_sub.script.utils.exceptions import FunctionRuntimeException
 from ytdl_sub.script.utils.exceptions import IncompatibleFunctionArguments
 from ytdl_sub.script.utils.exceptions import UserThrownRuntimeError
@@ -97,3 +98,10 @@ class TestFunction:
     def test_user_assert(self):
         with pytest.raises(UserThrownRuntimeError, match=re.escape("test this error message")):
             Script({"throw_error": "{%assert(False, 'test this error message')}"}).resolve()
+
+    def test_function_does_not_exist(self):
+        with pytest.raises(
+            FunctionDoesNotExist,
+            match=re.escape("Function %lolnope does not exist as a built-in or custom function."),
+        ):
+            Script({"dne": "{%lolnope(False, 'test this error message')}"}).resolve()