[TrueFurina]

Summary

Sequence.zip_with_next raises TypeError: 'map'/'filter' object is not subscriptable when it is chained after a lazy (non-PRE_COMPUTE) transform such as map, filter, select, etc.

Root cause

The transform is defined as:

def zip_with_next_t():
    return Transformation(
        "zip_with_next", lambda sequence: zip(sequence, sequence[1:]), None
    )

In the serial execution engine, a transform without PRE_COMPUTE receives the raw upstream iterator (not a list). Since zip_with_next subscripts its input (sequence[1:]), feeding it an iterator raises TypeError.

This is the same class of bug as #136 ("Reverse fails on sequences"), which was fixed for reverse by adding PRE_COMPUTE. The sibling transforms init, inits, tails, and sliding already use PRE_COMPUTE for exactly this reason — zip_with_next was simply missed when it was added in #217.

Fix

Mark zip_with_next_t with ExecutionStrategies.PRE_COMPUTE, matching its siblings. zip_with_next inherently needs the whole sequence (it pairs element i with i+1), so pre-computing is correct and does not change its semantics.

Verification

• Added regression test test_zip_with_next_after_lazy_transform (serial + parallel).
• Full suite: 311 passed, 3 skipped, 0 failures.