Custom panic exception

Now that we have a prelude!

Author: dusty-phillips

README.md

@@ -47,7 +47,6 @@ PRs are welcome.
 
 ### TODO
 
-- panic should probably raise a custom/stdlib exception instead of BaseException
 - custom types with unlabelled fields are not working
   - Given that labelled and unlabelled fields can be mixed on one class, I have a feeling we have to ditch dataclasses. Probably a custom class with slots, a dict of names to indices, and a custom **match_args** that can handle tuple-like _or_ record-like syntax?
 - some complex expressions aren't implemented yet

src/generator.gleam

@@ -76,7 +76,7 @@ fn generate_expression(expression: python.Expression) {
       generate_expression(expression) |> string_builder.prepend("not ")
     python.Panic(expression) ->
       generate_expression(expression)
-      |> string_builder.prepend("raise BaseException(")
+      |> string_builder.prepend("raise GleamPanic(")
       |> string_builder.append(")")
     python.Todo(expression) ->
       generate_expression(expression)

src/python_prelude.gleam

@@ -1,5 +1,8 @@
 pub const gleam_builtins = "
 import dataclasses
+
+class GleamPanic(BaseException):
+    pass
 "
 
 pub const prelude = "from gleam_builtins import *\n\n"

test/expression_test.gleam

@@ -146,7 +146,7 @@ pub fn empty_panic_test() {
     "from gleam_builtins import *
 
 def main():
-    raise BaseException(\"panic expression evaluated\")
+    raise GleamPanic(\"panic expression evaluated\")
     ",
   )
 }
@@ -161,7 +161,7 @@ pub fn string_panic_test() {
     "from gleam_builtins import *
 
 def main():
-    raise BaseException(\"my custom panic\")
+    raise GleamPanic(\"my custom panic\")
     ",
   )
 }