Using `it` as a Placeholder in JavaScript Pipeline Operator

## Motivation The current Hack-style pipeline proposal uses `%` as a placeholder for the left-hand value of `|>`. While functional, `%` has readability issues and conflicts with the modulo operator. This proposal suggests replacing `%` with `it`, which is more intuitive and avoids syntax conflicts. ## Proposal Introduce `it` as a context-sensitive keyword in pipeline expressions. It would act as a placeholder for the left-hand value, similar to `yield` in generators. ### Example ```js const result = 5 |> it * 2 |> foo(it) |> it + 3; // Equivalent to: foo(5 * 2) + 3 ``` ## Design Details 1. **Contextual Scope** - `it` is only valid inside pipeline expressions, preserving its use as a regular variable elsewhere. - Example: ```js let it = 42; const result = 5 |> it * 2; // `it` is 5 inside the pipeline console.log(it); // Still 42 outside ``` 2. **Comparison to `yield`** - Like `yield`, `it` is only special in a specific context. - Unlike `yield`, `it` is a simple placeholder without control-flow effects. 3. **Backward Compatibility** - Since `it` is not a reserved word, this proposal does not break existing code. - In case of name conflicts, pipeline-scoped `it` takes precedence. ## Advantages ✅ **Improved readability**: `it` makes expressions more natural compared to symbols like `%`. ✅ **Familiar syntax**: Similar to `it` in Kotlin and Ruby. ✅ **No conflict with `%` (modulo operator)**: ```js const result = 10 |> it % 3; // Clearly computes 10 % 3 ``` ## Potential Challenges 1. **Variable Name Conflicts** - If `it` exists in the outer scope, it might cause confusion. This is mitigated by giving `it` pipeline-specific precedence. 2. **Naming Debate** - Placeholder names are often controversial, but `it` offers a balance between clarity and compatibility. ## Comparison: `it` vs. `%` | Placeholder | Readability | `%` Conflict | Learning Curve | Compatibility | |------------|------------|-------------|--------------|--------------| | `%` | Low | Yes | Requires adaptation | Compatible | | `it` | High | No | Intuitive | Compatible | --- ## Conclusion Replacing `%` with `it` in pipeline expressions enhances readability, avoids conflicts with the modulo operator, and maintains backward compatibility.