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urbit/pkg/arvo/sur/xray.hoon
2020-11-20 15:23:56 -08:00

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::
:: These are the public types for the `xray` library. Analysing a type
:: yields an `ximage`, and everything else here is just some structure
:: within that.
::
:: `ximage`s can be printed as specs (hoon syntax for types), and can
:: be used to pretty-print typed data.
::
^? |%
::
:: An `xtable` is a graph of types referenced by the top-level type,
:: and the `root` `key` points to the node which corresponds to the
:: type under analysis.
::
+$ ximage [root=xkey =xtable]
::
:: A `xkey` is just an identifier for a node in the xray graph.
::
+$ xkey @
::
:: An `xtable` is the xray graph itself. It contains one node for for
:: the type that was analyzed and one node for every type referenced
:: within that type.
::
:: The `next` field is the the next available xkey (used when inserting
:: new xrays), `xrays` maps keys to graph nodes and `type-map` gives
:: the xkey corresponding to a type.
::
:: The `type-map` is basically just the reverse of the `xrays` map. It
:: doesn't contain any new information, but is needed for performance
:: reasons.
::
+$ xtable [next=xkey xrays=(map xkey xray) =type=(map type xkey)]
::
:: An `xray` is a node in the `ximage` graph. It contains everything
:: we know about a certain `type`. `key` is its identifier in the graph,
:: `type` is the type that it's an xray of, and `xdat` is the basic
:: information we derived about the type. The basic references to other
:: nodes are inside the `xdat` structure, though some of the other
:: fields may contain references as well.
::
:: - `xshape` is some more information about the xshape of data within
:: a cell.
:: - `xrole` expands on `xshape`, adding further information about the
:: xrole that a node has within a fork.
:: - `pats` is used for printing data: we want to know if this type
:: can be printed as a list, as json, as a tape literal, etc.
:: - `recipes` contains information about how a type was
:: constructed. It's used to get much nicer output when printing types.
:: - `studs` contains "standards names". I actually don't know what this is.
:: - `helps` contains all the documentation about a type.
:: - `loop` indicates whether or not a node references itself. The list
:: type is cyclical, for example. This is used when printing an
:: `ximage`.
::
+$ xray
$: =xkey
=type
xdat=(unit xdat)
xrole=(unit xrole)
pats=(unit xpat)
studs=(set stud)
recipes=(set recipe)
helps=(set help)
xshape=(unit xshape)
loop=(unit ?)
==
::
:: - `%void` -- impossible to create.
:: - `%noun` -- could be any noun.
:: - `%atom` -- An atom of some aura, possibly constant
:: - `%cell` -- A cell with a head and a tail.
:: - `%core` -- A core, its garb, its context type, and the types of
:: each of its arms.
:: - `%face` -- A face on another type.
:: - `%fork` -- Could be one or more other types.
:: - `%pntr` -- This is an internal hack, it should never survive
:: analysis; ignore.
::
+$ xdat
$@ ?(%noun %void)
$% [%atom =aura constant=(unit @)]
[%cell head=xkey tail=xkey]
[%core =garb xray=xkey batt=xbat]
[%face face=$@(term tune) xray=xkey]
[%fork =(set xkey)]
[%pntr xray=xkey]
==
::
:: The basic xshape of a type:
::
:: - `%void` -- impossible to create.
:: - `%noun` -- could be any noun.
:: - `%atom` -- always some type of atom; never a cell
:: - `%cell` -- always some type of cell; never an atom.
:: - `%junc` -- is a fork of a cell type and an atom type.
::
+$ xshape ?(%void %noun %atom %cell %junc)
::
:: A `xrole` is the of a type, including a more refined understanding
:: of what xrole it plays within a fork.
::
:: Nodes referenced within a `xrole` often do not actually exist in the
:: original type, since we need to reorganize forks in order to make
:: them more coherent.
::
:: - `%void` -- impossible to create.
:: - `%noun` -- could be any noun.
:: - `%atom` -- always some type of atom; never a cell
:: - `%constant` -- a cell type whose head is a constant atom.
:: - `%tall` -- a cell type whose head is an atom.
:: - `%wide` -- a cell type whose head is also a cell
:: - `%instance` -- a cell type whose head is a constant atom.
:: - `%option` -- a union of types which are all constant atoms.
:: - `%union` -- a union of types which are all instances (cells whose
:: head is a constant atom).
:: - `%junction` -- a union of an atom type and a cell type.
:: - `%conjunction` -- a union of two cell types, one of them %wide
:: and the other %tall.
:: - `%misjunction` -- any other union type. There's no efficient way
:: to tell which branch to take when analyzing a fork which is a
:: %misjunction, and the type is probably improperly constructed.
::
+$ xrole
$@ $? %void %noun %atom %tall %wide ==
$% [%constant =atom]
[%instance =atom]
[%option =(map atom xkey)]
[%union =(map atom xkey)]
[%junction flat=xkey deep=xkey]
[%conjunction wide=xkey tall=xkey]
[%misjunction one=xkey two=xkey]
==
::
:: This is just a utility type, it encodes the "battery" structure
:: within a core.
::
:: It's a map from chapter names to the documentation and arms within
:: that chapter.
::
+$ xbat (map term (pair what (map term xkey)))
::
:: A recipe tells us how a type was constructed.
::
:: - `%direct` is a simple type like `term`, or `xray`.
:: - `%synthetic` is a constructed type, like `(list @)`.
::
+$ recipe
$% [%direct =term]
[%synthetic =term =(list xkey)]
==
::
:: A `xpat` is high-level information about the shape of a type. This
:: is used for printing data.
::
:: This is fairly heuristic. [%a %b %c ~] is recognized as a `path`,
:: `[3 ~[4 5 6]]` is recognized as a list, etc.
::
:: Most of the xpats have names that make their purpose obvious:
:: for example, the %tape xpat means that data of type type can be
:: printed as if it had the `tape` type. However, `%gear` and `%gate`
:: might not be entirely obvious.
::
:: - The %gear xpat is any core with a cell subject.
:: - The %gate xpat is a core that looks like a gate.
::
+$ xpat
$@ ?(%hoon %manx %json %nock %path %plum %skin %spec %tape %tour %type %vase)
$% [%gate sample=xkey product=xkey]
[%gear sample=xkey context=xkey batt=xbat]
[%list item=xkey]
[%tree item=xkey]
[%unit item=xkey]
==
--