006 Space Lua Integrated Query

Context

With Space Lua as the one embedded language and an object index to query, users still need an ergonomic way to select and transform objects, the single most common thing they do (RFC indexes, task rollups, dashboards). Plain imperative Lua (loops, filters, maps) works but reads poorly for what is fundamentally a declarative query, and a separate query language would reintroduce the second-language seam that adopting Lua removed.

Decision

Add Space Lua Integrated Query (SLIQ) — an SQL- and LINQ-inspired query syntax embedded inside Lua, rather than a standalone language or a plain function API.

• Syntax: query[[ from ... where ... order by ... select ... ]]. The only mandatory clause is from; clauses can appear in any order.
• It’s backwards-compatible Lua. query[[...]] is just Lua’s call-with-a-long-string sugar (query("...")), so a program using SLIQ is still syntactically valid Lua — Space Lua simply interprets that string as a query.
• Every clause body is a Lua expression, so a query can run over the object index or any Lua table, call Lua functions, and render a template directly in select.

Consequences

Positive

• Declarative and familiar. SQL/LINQ-style reads far better than hand-rolled loops for the common select/filter/aggregate task.
• Still one language. SLIQ is sugar within Lua, not a separate DSL — it preserves the “one language, no seams” win of ADR/005 Space Lua (a query can select a template call, use Lua helpers, etc.).
• Uniform over any data. Because from takes a Lua expression, the same syntax queries indexed objects or arbitrary in-memory tables.

Negative / trade-offs

• A query dialect to parse and maintain. SLIQ is a syntax extension inside the custom Lua implementation — only feasible because the interpreter is our own (ADR/005 Space Lua).
• Looks like SQL but isn’t. Reorderable clauses and Lua-expression bodies can surprise users who expect strict SQL semantics.

Alternatives considered

• Plain Lua only (a filter/map library API). Rejected: verbose and imperative for what is usually a declarative query; poor readability for the most common use case.
• A separate standalone query language (as in v1). Rejected: reintroduces a second language and the seams between query, template, and script that ADR/005 Space Lua set out to remove.
• Pure SQL: implementing full SQL would be an immense project, and the gap between Lua and SQL semantics would be confusing.

References

• Space Lua/Integrated Query — full syntax and examples.
• Introduced as “Lua Integrated Query”: PR 1205, later rebranded SLIQ.