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The shopping cart rule engine DSL
time to read 1 min | 144 words
As the final example in the book, I am showing off a DSL for processing a shopping cart. Here is how it looks like:
behavior of preferred_customer upon bad_credit: authorize_funds cart.Total * 0.5, "For preferred customers we only authorize half the amount" upon cart_update: when cart.Total > 1000: add_cart_discount 5, "Preferred members gets 5% discount for orders over 1,000$"
And this:
behavior of default_customer
upon bad_credit:
authorize_funds cart.Total, "We require full authorization of the amount in low credit rating scenarios"
Where we defined preferred customer and default customer as:
define preferred_customer: customer.TotalPurchaseAmount > 5000 define default_customer: customer.TotalPurchaseAmount <= 5000
The implementation is surprisingly easy, and I was able to walk through the reasoning for this implementation rather than the usual when [condition] in a way that I hope would make sense.
You can look at the implementation here: https://rhino-tools.svn.sourceforge.net/svnroot/rhino-tools/BDSLiB/trunk
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