Environment Management (lfe_env.erl)

Purpose: Manage variable, function, macro, and record bindings.

Module: lfe_env.erl (252 LOC) - Location: src/lfe_env.erl

Environment structure:

-record(env, {
    vars = null,    % Variable bindings (map or orddict)
    funs = null,    % Function/macro bindings (map or orddict)
    recs = null     % Record definitions (map or orddict)
}).

Implementation:

Conditional compilation based on map availability:

-ifdef(HAS_MAPS).
    % Use maps module
-else.
    % Use orddict
-endif.

Variable operations:

add_vbinding(Name, Value, Env) -> Env
is_vbound(Name, Env) -> boolean()
get_vbinding(Name, Env) -> {yes, Value} | no
fetch_vbinding(Name, Env) -> Value  % throws if not found
del_vbinding(Name, Env) -> Env
add_vbindings([{Name, Value}], Env) -> Env  % Bulk add

Function operations:

Functions stored as {function, [{Arity, Definition}]}:

add_fbinding(Name, Arity, Value, Env) -> Env
is_fbound(Name, Arity, Env) -> boolean()
get_fbinding(Name, Arity, Env) ->
    {yes, Value} |              % Local function
    {yes, Mod, Func} |         % Imported function
    no

Imported functions stored as {Arity, Module, RemoteName}.

Macro operations:

Macros stored as {macro, Definition}:

add_mbinding(Name, Macro, Env) -> Env
is_mbound(Name, Env) -> boolean()
get_mbinding(Name, Env) -> {yes, Macro} | no

Important: Adding a macro shadows ALL function definitions with that name (because macros are expanded at compile-time).

Record operations:

add_record(Name, Fields, Env) -> Env
get_record(Name, Env) -> {yes, Fields} | no

Environment merging:

add_env(Env1, Env2) -> Env

Merges two environments, preferring Env1 bindings in case of conflicts.

Environment threading:

Environments are immutable:

Env0 = lfe_env:new(),
Env1 = lfe_env:add_vbinding(x, 42, Env0),
Env2 = lfe_env:add_vbinding(y, 100, Env1),
% Env0, Env1 unchanged

This enables:

• Safe concurrency
• Easy backtracking
• Clear scoping rules