Embeddable

[bash]

• Maximum for automatic church numerals (large numbers can overflow the stack)
• Maximum steps for beta-reduction
• Predefined definitions (with a warning if you shadow it)
• Option to disable syntax sugar such as automatic church numerals, definitions, etc.
• Spans that point to different files (so that the embedder can surround the user code with an application to pass in data–errors should point to a different "file" in that case)