lfe_qlc.erl - Query List Comprehension

Purpose: Transform LFE QLC syntax to Erlang's qlc module for database queries.

Location: src/lfe_qlc.erl Size: 51 LOC, 1.9KB

Module Classification: Library, QLC integration

Public API

transform(QlcForm) -> QlcExpression

Transform LFE QLC to Erlang qlc calls. Located at lfe_qlc.erl:39-42.

QLC Syntax

Purpose: Query databases (Mnesia, ETS, DETS) with comprehension-like syntax.

Example:

(qlc (lc ((<- p (: mnesia table person))
          (> (person-age p) 18))
      (person-name p)))

Translates to:

qlc:q([person_name(P) || P <- mnesia:table(person),
                          person_age(P) > 18]).

Transformation

Simple Delegation (transform/1 at lines 45-51):

Actually delegates to standard LFE list comprehension transformation, then wraps in qlc:q/1.

transform([qlc|ListComp]) ->
    ['call', 'qlc', 'q', transform_lc(ListComp)].

Dependencies

Erlang stdlib:

• qlc module (for runtime execution)

Used By

• User code querying Mnesia/ETS/DETS
• Database applications

Special Considerations

Thin Wrapper: Minimal module, mostly delegates to standard comprehension.

Runtime Dependency: Requires qlc application to be loaded.

Optimization: QLC can optimize queries across multiple tables (joins, filtering).