50 lines
2.6 KiB
Markdown
50 lines
2.6 KiB
Markdown
[](https://travis-ci.org/jsmaniac/remember)
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[](https://codecov.io/gh/jsmaniac/remember)
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[](http://jsmaniac.github.io/travis-stats/#jsmaniac/remember)
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[](http://docs.racket-lang.org/remember/)
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[](https://github.com/jsmaniac/remember/issues)
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[](https://creativecommons.org/publicdomain/zero/1.0/)
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remember
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========
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This Racket library provides a compile-time memoize feature. It allows
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remembering a value with `(remember-write! 'category 'value)`. In subsequent
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compilations, `(get-remembered 'category)` will return a set of all
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previously-remembered values.
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Installation
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============
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raco pkg install remember
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Example use case: the `phc-adt` library
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=======================================
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This library is used to implement "interned" structure and constructor types
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in the [`phc-adt`](https://github.com/jsmaniac/phc-adt) library. The `phc-adt`
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library needs to know the set of all structure and constructor types used in
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the program, and uses `remember` to automatically memoize structure
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descriptors and constructor names.
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When the `structure` macro defined in
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[`structure.hl.rkt`](https://github.com/jsmaniac/phc-adt/blob/refactor/structure.hl.rkt)
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encounters an unknown list of field names, it uses the `remember` library to
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append the tuple of field names to a user-specified file. That file is loaded
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in subsequent compilations, so that the tuple of fields is known to `phc-adt`.
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The memoized descriptors are used to know all possible structs that can
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contain a field with the desired name when accessing it with `(get instance
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field-name)`. The `get` macro can then retrieve the field's value using the
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right accessor (for example `(struct123-fieldname instance)`). Knowing all
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existing structures allows `get` to perform some kind of dynamic dispatch to
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obtain the appropriate accessor, for example using a `cond` which tests for
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all possible types.
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The `constructor` macro defined in
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[`constructor.hl.rkt`](https://github.com/jsmaniac/phc-adt/blob/refactor/constructor.hl.rkt)
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works in the same way, but remembers the name of the constructor's tag instead
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of field names. The memoization feature is used so that all uses of a
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constructor with a given name are equivalent, across all files.
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