M. Widera and C. Beierle. Detecting Common Elements of Types. In Stephen Gilmore, editor, Trends in Functional Program- ming, volume 2. Intellect, 2000.
We describe an algorithm approximating the following question: Given two types t1 and t2, are there instances sigma(t1) and sigma(t2) denoting a common element? By answering this question we solve a main problem towards a type checking algorithm for non-disjoint types that raises an error just for function calls that cannot be executed successfully. For dynamically typed functional languages such a type checker can extend actual soft typing systems in order to reject provably ill-typed programs.
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