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POHow far should I take referential transparency?
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copied!<p>I am building a website using erlang, mnesia, and webmachine. Most of the documentation I have read praises the virtues of having referentially transparent functions.</p> <p>The problem is, all database access is external state. This means that any method that hits the database is no longer referentially transparent.</p> <p>Lets say I have a user object in a database and some functions that deal with authentication.</p> <p>Referentially opaque functions might look like:</p> <pre><code>handle_web_request(http_info) -> is_authorized_user(http_info.userid), ... %referentially opaque is_authorized_user(userid) -> User = get_user_from_db(userid), User.is_authorized. %referentially opaque lots_of_other_functions(that_are_similar) -> db_access(), foo. </code></pre> <p>Referentially transparency requires that I minimize the amount of referentially opaque code, so the caller must get the object from the database and pass that in as an argument to a function:</p> <pre><code>handle_web_request(http_info) -> User = get_user(http_info.userid), is_authorized_user(User), ... %referentially opaque get_user(userid) -> get_user_from_db(userid). %referentially transparent is_authorized(userobj) -> userobj.is_authorized. %referentially transparent lots_of_other_functions(that_are_similar) -> foo. </code></pre> <p>The code above is obviously not production code - it is made up purely for illustrative purposes.</p> <p>I don't want to get sucked into dogma. Do the benefits of referentially transparent code (like provable unit testing) justify the less friendly interface? Just how far should I go in the pursuit of referentially transparancy?</p>

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