make_checkpoint.py: detect OCaml exceptions during loading#175
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The send_and_wait() function sends user code followed by a sentinel Printf as the next toplevel phrase. When the user code raises an exception (e.g. a failed proof or missing file), the OCaml toplevel catches it, prints the error, and continues to the next phrase, so the sentinel always appears regardless of success or failure. This means make_checkpoint.py silently creates checkpoints of broken or partial states. Fix: wrap each expression in try/with that emits a unique error sentinel (HOL_MCP_LOAD_ERROR) on exception. wait_for_line() detects this sentinel and reports the exception with a clear error message before the script can proceed to checkpointing. Also reject expressions containing ';;' (multiple toplevel phrases) upfront, since try/with can only wrap a single expression. The error message guides the user to place composite inputs in a file and load with needs or loadt instead. This does not affect the MCP server's interactive use, where the LLM reads the full output and sees exception messages directly. It only affects make_checkpoint.py's batch usage, where intermediate output is discarded and only sentinel arrival is checked.
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The send_and_wait() function sends user code followed by a sentinel Printf as the next toplevel phrase. When the user code raises an exception (e.g. a failed proof or missing file), the OCaml toplevel catches it, prints the error, and continues to the next phrase, so the sentinel always appears regardless of success or failure. This means make_checkpoint.py silently creates checkpoints of broken or partial states.
Fix: wrap each expression in try/with that emits a unique error sentinel (HOL_MCP_LOAD_ERROR) on exception. wait_for_line() detects this sentinel and reports the exception with a clear error message before the script can proceed to checkpointing.
Also reject expressions containing ';;' (multiple toplevel phrases) upfront, since try/with can only wrap a single expression. The error message guides the user to place composite inputs in a file and load with needs or loadt instead.
This does not affect the MCP server's interactive use, where the LLM reads the full output and sees exception messages directly. It only affects make_checkpoint.py's batch usage, where intermediate output is discarded and only sentinel arrival is checked.