79 lines
2.4 KiB
Markdown
79 lines
2.4 KiB
Markdown
# lib-laddertypes
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Rust Implementation of Ladder-Types (parsing, unification, rewriting, etc)
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<hr/>
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## Ladder Types
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In order to implement complex datastructures and algorithms, usually
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many layers of abstraction are built ontop of each other.
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Consequently higher-level data types are encoded into lower-level data
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types, forming a chain of embeddings from concept to `rock bottom' of
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byte streams. While a high-level type makes claims about the
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semantics of objects of that type, high-level types are ambiguous in
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regard to their concrete syntactical representation or memory
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layout. However for compositions to be type-safe, compatibility of
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concrete represenations must be ensured.
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For example in the unix shell, many different tools & utilities
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coexist. Depending on the application domain, each of them will
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potentially make use of different representational forms for the same
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abstract concepts. E.g. for the concept 'natural number', many
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representations do exist, e.g. with variation over radices,
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endianness, digit encoding etc.
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Intuitively, *ladder types* provide a way to distinguish between
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multiple *concrete representations* of the same *abstract / conceptual
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type*, by capturing the *represented-as* of layered data formats in
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the structure of type-terms. Formally, we introduce a new type
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constructor, called the *ladder type*, written `T1 ~ T2`, where `T1`
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and `T2` are types. The type-term `T1 ~ T2` then expresses the
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abstract type of `T1` being represented in terms of the concrete type
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`T2`, which can be read by "`T1` represented as `T2`".
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#### Example
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The following type describes a colon-separated sequence of timepoints,
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each represented as unix-timestamp written as decimal number in
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big-endian, encoded as UTF-8 string.
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```
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<Seq TimePoint
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~<TimeSince UnixEpoch>
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~<Duration Seconds>
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~ℕ
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~<PosInt 10 BigEndian>
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~<Seq <Digit 10>~Char>>
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~<SepSeq Char ':'>
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~<Seq Char>
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~UTF-8
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~<Seq Byte>
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```
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An object that fits the format described by this type could look like
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this:
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```
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1696093021:1696093039:1528324679:1539892301:1638141920:1688010253
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```
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## How to use this crate
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```rust
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use laddertypes::*;
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fn main() {
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let mut dict = TypeDict::new();
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let t1 = dict.parse("<A B~X C>").expect("couldnt parse typeterm");
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let t2 = dict.parse("<<A B~X> C>").expect("couldnt parse typeterm");
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assert_eq!( t1.clone().curry(), t2 );
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assert_eq!( t1, t2.clone().decurry() );
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}
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```
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## License
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[GPLv3](COPYING)
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