{"title":"A syntactic account of singleton types via hereditary substitution","authors":"Karl Crary","doi":"10.1145/1577824.1577829","DOIUrl":"https://doi.org/10.1145/1577824.1577829","url":null,"abstract":"We give a syntactic proof of decidability and consistency of equivalence for the singleton type calculus, which lies at the foundation of modern module systems such as that of ML. Unlike existing proofs, which work by constructing a model, our syntactic proof makes few demands on the underlying proof theory and mathematical foundation. Consequently, it can be --- and has been --- entirely formulated in the Twelf meta-logic, and provides an important piece of a Twelf-formalized type-safety proof for Standard ML.\u0000 The proof works by translation of the singleton type calculus into a canonical presentation, adapted from work on logical frameworks, in which equivalent terms are written identically. Canonical forms are not preserved under standard substitution, so we employ an alternative definition of substitution called hereditary substitution, which contracts redices that arise during substitution.","PeriodicalId":262518,"journal":{"name":"International Workshop on Logical Frameworks and Meta-Languages: Theory and Practice","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122928460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Higher-order constraint simplification in dependent type theory","authors":"J. Reed","doi":"10.1145/1577824.1577832","DOIUrl":"https://doi.org/10.1145/1577824.1577832","url":null,"abstract":"Higher-order unification is undecidable, but has fragments which admit practical algorithms, which are used extensively in logical frameworks. For example, it is decidable whether unification problems in the pattern fragment are solvable, and they enjoy unique most general unifiers when they are.\u0000 Often we wish to treat more general problems which are nonetheless solvable by incrementally reasoning about the parts of them that fall in the pattern fragment after more progress has been made --- to this end constraint simplification algorithms have been proposed, which work on the so-called dynamic pattern fragment. However, their theory turns out to be surprisingly subtle. The constraint simplification algorithm implemented in Twelf, for instance, is not terminating, despite the sketch of a proof of its termination in the literature. We describe and prove correct a new, terminating constraint simplification algorithm for a dynamic pattern fragment of higher-order unification in a dependent type system, and discuss its implementation.","PeriodicalId":262518,"journal":{"name":"International Workshop on Logical Frameworks and Meta-Languages: Theory and Practice","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123379048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Coercive subtyping in lambda-free logical frameworks","authors":"Robin Adams","doi":"10.1145/1577824.1577830","DOIUrl":"https://doi.org/10.1145/1577824.1577830","url":null,"abstract":"We show how coercive subtyping may be added to a lambda-free logical framework, by constructing the logical framework TF<, an extension of the lambda-free logical framework TF with coercive subtyping. Instead of coercive application, TF< makes use of a typecasting operation. We develop the metatheory of the resulting framework, including providing some general conditions under which typecasting in an object theory with coercive subtyping is decidable. We show how TF< may be embedded in the logical framework LF, and hence how results about LF may be deduced from results about TF<.","PeriodicalId":262518,"journal":{"name":"International Workshop on Logical Frameworks and Meta-Languages: Theory and Practice","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130987365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}