Module defarg

Authors: Serge Aleynikov (saleyn(at)gmail(dot)com).


Erlang parse transform for permitting default arguments in functions

Presently the Erlang syntax doesn't allow function arguments to have default parameters. Consequently a developer needs to replicate the function definition multiple times passing constant defaults to some parameters of functions.

This parse transform addresses this shortcoming by extending the syntax of function definitions at the top level in a module to have a default expression such that for A / Default argument the Default will be used if the function is called in code without that argument.

   test(A / 10, B / 20) ->
     A + B.
The code above is transformed to:
   -export([t/0, t/1]).
   test()    -> test(10);
   test(A)   -> test(A, 20);
   test(A,B) -> A+B.
The arguments with default values must be at the end of the argument list:
   test(A, B, C / 1) ->    %% This is valid
   test(A / 1, B, C) ->    %% This is invalid
Default arguments must be constants or arithmetic expressions. Function calls are not supported as default arguments due to the limitations of the Erlang parser.

Function Index

parse_transform/2parse_transform entry point.

Function Details


parse_transform(AST, Options) -> any()

parse_transform entry point