Ranges, Slicing, Fold, And Pipeline Follow-Ups

The implemented range, slicing, fold, pipeline, and Sequence<T> baseline is archived in archive/ranges_slicing_pipeline_baseline.md.

This active document tracks only future collection-syntax work.

Remaining Scope

• Range step syntax and semantics.
• Multi-sequence zip/map2 and zip-with forms.
• N-ary fold over functions with more than one sequence input.
• Postfix fold expressions targeting imported, native, generic, or indirect function values.
• A richer Sequence<T> standard-library algorithm layer beyond the current size/get protocol.
• A final decision for standalone ? syntax outside the fixed ?... filter marker.

Dependencies

• Implemented baseline: Constant Generic Parameters
• Implemented baseline: Standard Library Modularization
• Related active work: Enhanced Tuple Follow-Ups

Acceptance Criteria

• Future range/fold extensions must preserve the existing distinction: |> is pipeline call composition, while postfix ... drives fold/map/filter.
• Multi-sequence forms must reject length or shape ambiguity explicitly rather than silently truncating unless a later design specifies truncation.
• Imported/generic fold targets need STUPID and ORGASM parity tests before the feature is considered complete.