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| Content Provider | ACM Digital Library |
|---|---|
| Author | Johann, Patricia Voigtländer, Janis |
| Abstract | Parametric polymorphism constrains the behavior of pure functional programs in a way that allows the derivation of interesting theorems about them solely from their types, i.e., virtually for free. Unfortunately, the standard parametricity theorem fails for nonstrict languages supporting a polymorphic strict evaluation primitive like Haskell's seq. Contrary to the folklore surrounding seq and parametricity, we show that not even quantifying only over strict and bottom-reflecting relations in the \$\forall\$-clause of the underlying logical relation --- and thus restricting the choice of functions with which such relations are instantiated to obtain free theorems to strict and total ones --- is sufficient to recover from this failure. By addressing the subtle issues that arise when propagating up the type hierarchy restrictions imposed on a logical relation in order to accommodate the strictness primitive, we provide a parametricity theorem for the subset of Haskell corresponding to a Girard-Reynolds-style calculus with fixpoints, algebraic datatypes, and seq. A crucial ingredient of our approach is the use of an asymmetric logical relation, which leads to "inequational" versions of free theorems enriched by preconditions guaranteeing their validity in the described setting. Besides the potential to obtain corresponding preconditions for standard equational free theorems by combining some new inequational ones, the latter also have value in their own right, as is exemplified with a careful analysis of seq's impact on familiar program transformations. |
| Starting Page | 99 |
| Ending Page | 110 |
| Page Count | 12 |
| File Format | |
| ISSN | 03621340 15581160 |
| DOI | 10.1145/982962.964010 |
| Journal | ACM SIGPLAN Notices (SIGP) |
| Volume Number | 39 |
| Issue Number | 1 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 1983-05-01 |
| Publisher Place | New York |
| Access Restriction | One Nation One Subscription (ONOS) |
| Subject Keyword | Correctness proofs Theorems for free Program transformations Denotational semantics Parametricity Controlling strict evaluation Haskell Logical relations Short cut fusion |
| Content Type | Text |
| Resource Type | Article |
| Subject | Computer Graphics and Computer-Aided Design Software |
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