It is not clear, what symbol is used in Notation function description for arrows? How to enter it in textual mode within Workbench?
The Notation function is part of the Notation package. You need to load the package first, then you can use the Notation palette to simply paste the Notation template and fill the placeholders.
If you cannot use the notation palette,for ex. because you are using a code editor like in WB, then you use the notation template with option Action -> PrintNotationRules. The Notation templates are user interfaces to easily input NotationMakeExpression and/or NotationMakeBoxes commands. So my suggested workflow is the following:
The output are NotationMakeExpression and/or NotationMakeBoxes cells. Select the contents of these cells and paste them in the code cells of your .m file in WB. Of course you must also have a Needs["Notation`"] command present in your .m file.
Personally I use a different workflow for my packages (my WildCats package heavily uses the Notation package). I use WB calling MMA as editor of my .nb files which autogenerate the .m files for my package. I described this technique here.
You can read the documentation page:"Options and Auxiliary Functions". At the end the section :"The Option Action" the option Action -> PrintNotationRules is explained.
Happy Notation creation! :-)