SQL expression pseudo calls

SQL expression pseudo-calls

QDB uses call-shaped AST nodes for SQL semantics that do not map one-to-one to a runtime function. They preserve information through parsing and logical plan rewrites, then qdb/kernel/annotate_type.cpp expands them once operand types and nullability are known.

Keep this list updated when adding another call name handled specially by InferType, ExpandNullable, or kernel generation.

Expansion-only calls

Call	Produced by	Expansion
qdb_in_list(lhs, item...)	SQL scalar IN (...)	Binds lhs once, hoists its nullable guard, and builds equality/OR expressions over its plain value. Per-item three-valued logic remains only for nullable items. The call never reaches Qumir name resolution.
strcat(a, b)	SQL `a
regexp_replace(str, pattern, replacement)	SQL function syntax	Constant pattern and replacement are registered once per query, then the call becomes qdb_regexp_replace(__arena__, __regexes__[id], str). The current three-argument form replaces only the first match; flags are not supported yet.
qdb_string_view_sql_like(str, pattern)	SQL str LIKE pattern	When pattern is a constant with no _, the expander picks a direct match from the shape of its %: none is qdb_like_equals, a trailing % is qdb_like_prefix, a leading % is qdb_like_suffix, both are qdb_like_contains. These run a memcmp or memmem on the string bytes. Any other pattern keeps the general matcher qdb_string_view_sql_like.
coalesce(a, ...)	SQL function syntax	Becomes a typed if chain selecting the first valid argument.

qdb_in_list unwraps Nullable[T] internally only after testing Valid. There is intentionally no standalone qdb_unwrap_nullable call: an unguarded unwrap would make it easy to discard SQL NULL semantics.

The native executor compiles regular expressions with PCRE2, while the browser executor uses JavaScript's ECMAScript RegExp. The engine does not currently validate a common regex subset, so engine-specific constructs may compile or behave differently between native and browser execution. Portable queries must use constructs with equivalent semantics in both dialects.

Semantic bridge calls

These names have implementations or overloads in qdb/modules/qumirdb.oz, but QDB typing also recognizes them specially because their SQL null behavior is not ordinary null propagation.

Call	Contract
qdb_sql_null()	Represents a bare, initially untyped SQL NULL. Its enclosing expression supplies the eventual Nullable[T] value type.
qdb_is_null(x)	SQL IS NULL: !x.Valid for Nullable[T], and constant false for non-nullable T.
qdb_is_true(x)	Predicate boundary used by WHERE, HAVING, join residuals, and CASE WHEN. It accepts a row only when the SQL value is true; NULL is not true.

Kernel placeholders

__arena__ and __regexes__ are identifier placeholders rather than calls. Filter and project kernel generation declares them as the opaque per-invocation string scratch arena and the query-local compiled-regex handle table. Computed sort, grouping, aggregate, and window expressions are materialized by a project before their key kernels. A regex call left directly in a join or low-level aggregate kernel is rejected explicitly instead of reaching the linker.