The Ultimate Conditional Syntax #260
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The Ultimate Conditional Syntax
Functional programming languages typically support expressive patternmatching syntax allowing programmers to write concise and typesafe code, especially appropriate for manipulating algebraic data types. Many features have been proposed to enhance the expressiveness of stock patternmatching syntax, such as pattern bindings, pattern alternatives a.k.a. disjunction, pattern conjunction, view patterns, pattern guards, pattern synonyms, active patterns, iflet patterns, multiway ifexpressions, etc. In this paper, we propose a new patternmatching syntax that is both more expressive and we argue simpler and more readable than previous alternatives. Our syntax supports parallel and nested matches interleaved with computations and intermediate bindings. This is achieved through a form of nested multiway ifexpressions with a conditionsplitting mechanism to factor common conditional prefixes as well as a binding technique we call conditional pattern flowing. We motivate this new syntax with many examples in the setting of MLscript, a new MLfamily programming language. We describe a straightforward desugaring pass from our rich source syntax into a minimal core syntax that only supports
Cheng, Luyu, and Lionel Parreaux. “The Ultimate Conditional Syntax. Proceedings of the ACM on Programming Languages, vol. 8, no. OOPSLA2, Oct. 2024, pp. 9881017. Crossref, https://doi.org/10.1145/3689746.
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