loop-semantics.md

Loop modifier semantics

Issue #6 investigated how reversed, limit, and offset interact. Tests used Shopify Liquid v5.10.0 and this Go implementation with the array [1, 2, 3, 4, 5].

The implementations differ when reversed appears with limit or offset.

Observed results

Modifiers	Shopify Liquid v5.10.0	This implementation
reversed	54321	54321
limit:2	12	12
offset:2	345	345
reversed limit:2	21	54
limit:2 reversed	12	54
limit:2 offset:1	23	23
offset:1 limit:2	23	23
reversed limit:2 offset:1	32	43
reversed offset:1 limit:2	32	43
limit:2 offset:1 reversed	23	43
offset:1 limit:2 reversed	23	43

Shopify Liquid behavior

In the tested Ruby version, reversed is recognized only before named parameters. The renderer applies offset, then limit, then reversed.

For reversed limit:2, it selects [1, 2] and reverses that slice to [2, 1]. For limit:2 reversed, the parser ignores reversed, so the result remains [1, 2].

This implementation

The Go parser accepts reversed in any modifier position. The renderer applies modifiers in this fixed order:

1. reversed
2. offset
3. limit

The template order does not change the result. For example, both reversed limit:2 and limit:2 reversed reverse the full array and then select [5, 4].

The relevant code is applyLoopModifiers in tags/iteration_tags.go. Regression tests belong in tags/iteration_tags_test.go.

This behavior is a known compatibility difference. Changing it requires a deliberate compatibility decision rather than a local parser or renderer cleanup.