When designing and implementing a new language, it is best to start by creating a grammar for the elements in your language, keeping in mind the semantics of each element as you go along.

For instance, your assignment might take on the form

<assign> =: <assign-token> "->{\n" <assign-list> "}\n"

<assign-token> =: "\w+"

<assign-list> =: <assign-element> <assign-list> 
                 | (null)

<assign-element> =: "[0-9]+\n"
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where nonterminal elements are in <> and literals and regexes are in "".

Once you have created a grammar you can implement it using Parse::RecDescent or your own recursive desecnt set of routines. Once you have the parser working, you can begin to create the translation routines.

Programming macro languages can be a bit tricky due to expansion rules. What gets expanded when? How do I quote expressions to prevent expansions? And so on. Two good examples of macro languages that deal with these issues are m4 and TeX. Both have good documentation.