Match Specification DSL

Purpose: Make ETS/trace match specifications readable.

Module: lfe_ms.erl (387 LOC)

Problem: Erlang match specs are cryptic:

%% Erlang match spec
[{{'$1', '$2'}, [{'>', '$2', 10}], ['$1']}]

Solution: LFE DSL:

(ets-ms
  ([(tuple key val)]
   (when (> val 10))
   key))

Compilation (src/lfe_ms.erl:52-67):

flowchart TD
    A["LFE Clauses<br/>[Pattern, (when Guards), Body]"] --> B["clause/2"]
    B --> C["Expand head<br/>(pattern matching)"]
    C --> D["Expand guards<br/>(test expressions)"]
    D --> E["Expand body<br/>(action expressions)"]
    E --> F["Generate:<br/>{tuple, Head, Guard, Body}"]

Variable binding:

• First occurrence of variable → Assign new $N, store binding.
• Subsequent occurrences → Use same $N.

Dollar variables numbered from 1 (Erlang-compatible).

Example:

(ets-ms
  ([(tuple key val)]
   (when (> val 10))
   val))

;; Expands to:
[{{'$1', '$2'}, [{'>', '$2', 10}], ['$2']}]