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Hello all, TypeScript team member here. This example actually is supported by TypeScript. See here for a demonstration. <http://www.typescriptlang.org/play/index.html?ssl=40&ssc=1&pln=39&pc=57#code/MYewdgzgLgBBMF4YG8C+MA+GYCIcG4BYAKBKgE8AHAUxgBkBLaAHgBUA+RFEmXmAC2oBDACYAuGKwA0PPlCEMANhMYsOJdNjABXRYqKliFGjACSYKNQDm1AE6rYSZLN6DREnQFsARnZnE+GHklCXNLG3smKBc4bU8PON9bDUwYHT0DElBIWGUzC2s7By5nAL43cRgAVn9A4Lz0xVq+CDiJKo1M4mzoGEUAJhUo5i8kziRFGCF4MMLI6C7jWgBRAA9KRRARBjArBzZx7jLXYUrpGOp1zZFqCTWNrZ294fvrp-2OdhStXX0SMiotFmEVeIAgDHAJRiFQSPj8FyuW1uMFB212+2BdlB4PA7GavFa8TSiTs32JGX+3XAvWRmNs2IhYChxwEp3a+JglweNwSeg5hPanUpPVg1EGKMRaOeLFGdkOtGm+XCWMROLABiAA> Best, Ben On Tue, Feb 18, 2020 at 1:14 PM Martin Abadi <[email protected]> wrote: > [ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list > ] > > Hello, > > TypeScript <https://www.typescriptlang.org/> has parameterized recursive > definitions and structural subtyping. The language has evolved over time, > and I am afraid I have not looked at the current definitions, but, early > on, the designers were aware of some of the algorithmic difficulties > that François Pottier mentions and introduced restrictions to avoid them. I > don't know whether the examples of interest to Isaac Oscar Gariano would be > expressible. > > Regards, > Martin > > > On Tue, Feb 18, 2020 at 10:36 AM François Pottier < > [email protected]> > wrote: > > > [ The Types Forum, > http://lists.seas.upenn.edu/mailman/listinfo/types-list > > ] > > > > > > Hello, > > > > If I am not mistaken, already deciding the *equivalence* of two types > > in the presence of recursive and parameterized type abbreviations is > > extremely costly: Marvin Solomon proved it equivalent to the DPDA > > equivalence problem ("Type definitions with parameters", POPL'78). > > > > -- > > François Pottier > > [email protected] > > http://cambium.inria.fr/~fpottier/ > > >
