Functional programming in ML

I have this datatype defined:

Code:

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datatype 'a somedata = empty | data of string * string * 'a somedata list;

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how could I write a function that would print this out? :(

I tried something like this :

Code:

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fun print (empty) = [empty] | print (data(birka,vertiba,[somedata])) = print([somedata]); | printxml data(birka,vertiba,[empty]) = [empty];

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thanks!

Another thing:

I hate to ask this, but is there a possibility to ASSIGN a value to a variable in a if-then construction? If-then is supposed to be an expression-operator, rather, than a statement. Does that make it like a function being able only to return values and not contain blocks of code?