67 lines
2 KiB
Markdown
67 lines
2 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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*Ladder Types* provide a way to distinguish between multiple *concrete
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representations* of the same *abstract / conceptual type*.
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The intuition is to capture a 'represented-as' relation in the
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structure of a type term. Formally, we introduce a new type
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constructor, called the *ladder type*, written as `T1 ~ T2`, where
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`T1` and `T2` are types. The term `T1 ~ T2` can be read by `T1 is
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represented as T2`.
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This can be particularly useful in contexts where no standard
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representational forms exist, e.g. in the unix shell where many
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different tools & utilities come into contact, each making use of
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potentially different representational forms, depending on the
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application domain.
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Trying to introduce a global type system at IPC level would result in
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naming conflicts: Abstract concepts like 'natural number' do not have
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any standard representational form, as it is the case with other more
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contained languages. With a simple type name like this it is not clear
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which of the many equivalent representations is required, e.g. for an
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*integer number* variations over radices, endianness, digit encoding
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etc. exist.
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Usually, many layers of abstraction are built ontop of each other,
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where higher-level data types are encoded into lower-level data types,
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forming a chain of embeddings from concept to `rock bottom' of byte
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streams.
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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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### License
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[GPLv3](COPYING)
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