lfe_macro_struct.erl - Struct Macro Generator

Purpose: Generate accessor macros for struct (map-based) definitions.

Location: src/lfe_macro_struct.erl Size: 46 LOC, 1.5KB

Module Classification: Compiler support, code generation

Public API

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

Generate struct macros. Located at lfe_macro_struct.erl:42.

Struct vs Record

Structs use maps instead of tuples:

(define-struct [name age city])

(struct person name "Alice" age 30)
→ #{__struct__ => person, name => "Alice", age => 30, city => undefined}

Key Difference: Structs include a __struct__ key identifying the struct type (Elixir-inspired).

Generated Macros

Fewer macros than records (structs use runtime functions):

1. Module functions (not macros):

   • __struct__/0 - Return default struct
   • __struct__/1 - Create struct from proplist

2. Accessor macros:

   • struct - Constructor macro
   • is-struct - Type test macro
   • struct-field - Field access macro

Struct Runtime

Struct operations are defined in lfe_struct.erl (33 LOC):

new(Mod) -> Mod:'__struct__'().
new(Mod, Fields) -> Mod:'__struct__'(Fields).
is(Struct, Mod) -> maps:get('__struct__', Struct) =:= Mod.
fetch(Struct, Mod, Field) -> maps:get(Field, Struct).
...

Dependencies

• lfe_struct (runtime)
• maps (Erlang)

Used By

• lfe_macro - Expands defstruct forms

Special Considerations

Flexibility: Maps are more flexible than tuples:

• Can add fields dynamically
• Pattern matching on maps
• Better introspection

Performance: Map access is slower than tuple element access

OTP Compatibility: Less compatible with OTP than records (some behaviors expect records)