fix(language): a where string names several columns in at's over= and into=, as an expression does

[FBumann]

Prompt: "Discuss hs request with me" … "Do all 3" … "post it and fix the issue with a PR"

Note

The following content was generated by AI.

A where: string now accepts at(p, by=r, over=a, into=[b, c]) and a list in over=, as an expression already did. Before, it failed to parse. The bracketed name list is now one grammar element that both parsers use.

Closes #781.

What this changes

• _expression_parser.NAME_LIST is the bracketed name list, moved to module level. The expression grammar and the where grammar both read a kwarg value as a quoted keyword, a name list, or arithmetic.
• The where resolver already read a list through relation_ref, so nothing changes there. The read is held to the same rules as at in an expression.
• expressions.md says that over= and into= each name one column or a list, in a where: too.

Why

A piecewise block in #630 with a where: and a link that walks into: [flow, effect] writes this where: into its rows and assumptions. That load failed with SchemaError: Assertion failed, what a method assumes is stated in the language. fluxopt's investment cost curve (fluxopt/fluxopt#26) has that shape.

Test, gates, and what was not run

Test. TestAPredicateIsAnOperand::test_a_read_names_several_columns_as_an_expression_does, parametrized by into-names-several-columns and over-names-several-columns. Each case loads a constraint with the list, checks the mask's dims and what it reads, checks that to_yaml() loads again to the same program, and checks that markdown, LaTeX and Typst print the operand and the relation.

Without the fix (the src/ change stashed), both cases fail:

E   mathspec.errors.SchemaError: Constraint 'k': Failed to parse where string: 'at(has_curve, by=cost_of, over=curve, into=[flow, effect])'
E   mathspec.errors.SchemaError: Constraint 'k': Failed to parse where string: 'at(has_cost, by=pair_of, over=[flow, effect], into=curve)'
2 failed

Gates run in a uv venv (Python 3.12) with the pinned tool versions, since pixi cannot be installed here:

Gate	Result
pytest -q -n auto	2597 passed, 2 skipped
ruff check, ruff format --check (0.16.1)	clean
pyrefly check (1.2.0)	0 errors
prettier --check on expressions.md, typos	clean
docs-build, compile-tex	not run: the proxy refuses docs.python.org, and there is no tectonic

Not done: #630 is not changed here. Once this merges, #630 takes main and adds its block with where: and into: [flow, effect] as a regression test.

🤖 Generated with Claude Code

https://claude.ai/code/session_015VUkQfE5dT7mEGoTQXSxN3

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2 files changed

± changelog/index.html
± reference/language/expressions/index.html