Diagnosing APL Off-by-One Errors from the ⎕IO Index Origin
Find and fix APL off-by-one indexing errors caused by the ⎕IO index origin setting, with checks, scoped fixes, and escalation criteria.
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aplAPL ⎕IO index origin portability across implementations and saved workspaces
Context Teams adopting APL for repeatable development environments face a configuration boundary: the session-wide index origin ⎕IO defaults to 1 in traditional code bases but 0 in scripts targeting Python interoperability. Dyalog APL, GNU APL, and NARS2000 all honor the variable, yet none persist its value in a saved workspace ( )SAVE or ⎕CY copy). On resta
⎕IO Propagation Across dfns: Nested Array Rank Divergence
The ⎕IO assignment in dfns exhibits implementation‑dependent propagation when nested arrays are reduced or indexed. In Dyalog APL, a simple vector retains rank 1 when the index origin is set to 0, while GNU APL may classify it as rank 0, causing reduction operators to yield different results. This divergence affects large‑scale data pipelines that assume a u