CODEWITHSUNDEEP
erlang
sergeyz
sergeyz

Reputation: 1328

Retrieve value by variable name in erlang function

Is it possible somehow to retrieve variable value by its name (name represented as string)?

% we are calling foo function as foo(3)
foo(Param) ->
    Var1 = Param * 2,
    % some magic code here which can evaluate 
    % "Var1" string to Var1's value (6)
    ok.

I want to implement (if it is possible) some kind of logger macro, like

Param = 3*4,
% This should write "My parameter value is 12" to log
?LOG("My parameter value is $Param").

Thanks.

Upvotes: 1

Views: 452

Answers (3)

sergeyz
sergeyz

Reputation: 1328

Thanks to Dmitry Belyaev for mentioning parse transform. Say we have logging code:

?dump("My parameter value is $Param")

What I need here is to parse variables within format string ("My parameter value is $Param") with some regular expression. This format string contains single var name (Param). And we need to insert io_lib:format function call (by transforming original AST) with modified format string: 

print_message(io_lib:format("My parameter value is ~p~n", [Param]))

In result we can archive required behavior:

Bar = "hello",
Buzz = buzz123,    
?dump("Say $Bar to $Buzz"),
% => example:19: Say "hello" to buzz123

You can look at my implementation here

Upvotes: 1

Dmitry Belyaev
Dmitry Belyaev

Reputation: 2593

The common way to log is to have formatting string and list of parameters. However your idea is achievable through usage of parse transform.

Upvotes: 1

Tilman
Tilman

Reputation: 2005

For toy problems you could use:

io:format("My parameter value is ~p~n", [Param]).

See io_lib and io.

Alternatively:

error_logger:info_report/1

or other error_logger functions.

The logging library lager is commonly used.

Upvotes: 0

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