lfe_macro_record.erl - Record Macro Generator

Purpose: Generate accessor macros for record definitions.

Location: src/lfe_macro_record.erl Size: 122 LOC, 4.5KB

Module Classification: Compiler support, code generation

Public API

define(Name, FieldDefs, Env, Line) ->
    {[{Name, Macros}], Env}

Generate record macros. Located at lfe_macro_record.erl:44-56.

Generated Macros

For a record definition:

(define-record person
  name
  age
  (city "Unknown"))  ; With default

9+ Macros Generated:

1. make-person - Constructor

   (make-person name "Alice" age 30)
   → (tuple 'person "Alice" 30 "Unknown")
   

2. is-person - Type test

   (is-person x)
   → (andalso (is_tuple x) (=:= (tuple-size x) 4) (=:= (element 1 x) 'person))
   

3. match-person - Pattern matcher

   (match-person name n age a)
   → (= (tuple 'person n a _) x)
   

4. update-person - Updater

   (update-person p age 31 city "NYC")
   → (setelement 3 (setelement 4 p "NYC") 31)
   

5. set-person - Updater (deprecated alias for update-person)

6. fields-person - Field list

   (fields-person)
   → (list 'name 'age 'city)
   

7. size-person - Record size

   (size-person)
   → 4
   

8. person-field (one per field) - Getter

   (person-name p)    → (element 2 p)
   (person-age p)     → (element 3 p)
   

9. set-person-field (one per field) - Setter

   (set-person-name p "Bob")
   → (setelement 2 p "Bob")
   

Tuple Layout

Records compile to tuples with tag as first element:

(make-person name "Alice" age 30)
→ #(person "Alice" 30 "Unknown")
  ^^^^^^  ^^^^^^^  ^^   ^^^^^^^^^
  tag     name     age  city

Field Indexing: 1-based (element 1 is tag, element 2 is first field, etc.)

Erlang Compatibility

LFE records are identical to Erlang records:

% Erlang code can use LFE records:
-include("person.hrl").  % If generated

P = {person, "Alice", 30, "Unknown"},
Name = P#person.name,   % "Alice"

Dependencies

• lfe_lib - Utilities
• lists - List operations

Used By

• lfe_macro - Expands defrecord forms

Special Considerations

Macro Count:

For an N-field record:

• Base macros: 7
• Field accessors: N getters + N setters
• Total: 7 + 2N macros

For 10-field record: 27 macros generated!

Naming Conflicts:

If you define:

(define-record foo bar)

The following names are reserved:

• make-foo, is-foo, match-foo, update-foo, set-foo, fields-foo, size-foo
• foo-bar, set-foo-bar

Default Values:

(define-record person
  name           ; No default (will be 'undefined' if not specified)
  (age 0)        ; Default: 0
  (city "Stockholm"))  ; Default: "Stockholm"

Performance: Record access compiles to direct element/2 calls - very fast.