Implimenting issue #887 - Adding an optional if or for at the end of a comp function.

[ad4mf06]

Summary

This PR implements issue #887 by adding support for optional if and for clauses at the end of pattern-matching comprehensions.

Changes

grammar.py (line 1969)

Added .Optional(comp_iter) at the end of match_comp_for, allowing an optional if or for clause to be appended to a pattern-matching comprehension.

compiler.py (line 4597)

Modified the match_comp_expr_handle function to handle the optional extra comprehension clauses:

• If len(match_for_group) == 2: the group contains only matches and iterable (no extra clauses).
• If len(match_for_group) > 2: the third element and beyond are joined into extra_comp_clauses, which are appended to the generated Python comprehension expression.

Extra clauses are also handled for expr_setnames context: any variables introduced by for clauses in extra_comp_clauses are extracted via regex and removed from new_names to avoid false positives in scope analysis.

tests/src/cocotest/agnostic/primary_2.coco

Added a comprehensive test suite for pattern-matching comprehensions covering:

• Basic match comprehension with CompPair and CompTriple data types
• Extra for clauses after the pattern match
• for + if combinations on loop variables
• if filtering on pattern variables (single and multiple conditions)
• Dict, set, and generator comprehensions with pattern matching
• Combined conditions using and

[evhub]

I think it's a bit confusing for only the first comprehension to have the ability to be a pattern-matching comprehension. My preference here is to either stick with the current implementation that only allows one comprehension, or to support arbitrary mixing and matching of standard and pattern-matching comprehensions (the ideal, but annoying to implement).

[ad4mf06]

Thanks for the feedback! I've updated the PR to implement the ideal option — arbitrary mixing and matching of standard and pattern-matching comprehensions.

The approach works by adding two new grammar rules (inner_match_comp_for with explicit match keyword, and implicit_inner_match_comp_for without) to comp_iter, which is the recursive clause rule. This means pattern-matching for
clauses can now appear in any position and in any combination with standard for/if clauses: