'eval-cxt objects are callable, and their call is equivalent to:
(let ob (eval-cxt)
(ob x))
==>
(let ob (cxt)
(eval:ob x))
The implementation is free to define 'cxt and/or 'eval-cxt objects in terms of Arc axioms or by adding them as implementation-specific axioms.
The context object accepts a plain read expression (with unpackaged symbols) and emits an s-expression where all symbols are packaged symbols.
It is the context object which keeps track of the current package, so you might have some accessor functions to manipulate the context object (e.g. destructure it into the current package, etc.).
The read function is stateless and simply emits unpackaged symbols, and emits packaged symbols if and only if the given plaintext specifically includes a package specification.
A package object is a stateful, synchronized (as in safely accessible across different threads, and whose basic operations are assuredly atomic) object. A context is a stateful object intended for thread- and function- local usage.
context objects
===============
A context object is callable (and has an entry in the axiom::call* table) and has the following form:
(let ob (cxt)
(ob expression))
The return value of the context is either of the following:
1. If the expression is one of the following forms (the first symbol in each form is unpackaged, 'symbol here is a variable symbol):
(in-package symbol)
(interface symbol . symbols)
(using symbol)
(import symbol symbol)
...then the return value is axiom::t, and either the context's state is changed, or the state of a package (specifically the current package of the context) is changed.
2. For all other forms, it returns an equivalent expression, but containing only packaged symbols. The state of the context is not changed.
The forms in number 1 above have the following changes in the context or current package of the context:
(in-package symbol)
Changes the current package of the context to the package represented by the unpackaged symbol. The implementation is free to throw an error if the given symbol is packaged.
(interface symbol . symbols)
Defines an interface. All symbols are first applied to the current package to translate them into packaged symbols, if they are unpackaged (this translation by itself may change the package's state, and also a packaged symbol will simply be passed as-is by the package object; see section "package objects" below). It then modifies the package of the first symbol to have an interface whose symbols are the given symbols.
If the interface already exists, it is checked if the lists are the same to the existing list. If it is not the same, the implementation is free to throw an error.
(using symbol)
The given symbol must be a packaged symbol. It must name an interface of its package; if the interface does not exist on the package, the implementation must throw an error. For each symbol in the interface, this changes the current package's state, creating or modifying the mapping from the unpackaged symbol of the same name to the symbol in the interface.
For conflicting package interfaces: let us suppose that the context is in package 'User, and there exists two package interfaces, A::v1 and B::v1. A::v1 is composed of (A::foo A::bar) while B::v1 is composed of (B::bar B::quux). If the context receives (using A::v1), the User package contains the mapping {foo => A::foo, bar => A::bar}. Then if the context receives (using B::v1), the User package afterwards contains the mapping {foo => A::foo, bar => B::bar, quux => B::quux}.
(import symbol symbol)
Forces the current package to have a specific mapping. The first symbol must be a packaged symbol and the second symbol must be unpackaged. The implementation must throw an error if this invariant is violated.
Continuing the example above, after (import A::bar A-bar), this changes the package to {foo => A::foo, bar => B::bar, A-bar => A::bar, quux => B::quux}
package objects
===============
A package object is callable and has the following form:
(ob expression)
expression must evaluate to a symbol, and if a non-symbol is applied to a package object, the implementation is free to throw an error. The application otherwise evaluates to either:
1. The same symbol, if the given symbol is a packaged symbol; this does not change the state of the package
2. A packaged symbol, if the given symbol is an unpackaged symbol. If the package does not contain a mapping for the unpackaged symbol, the state of the package is changed so that a mapping for the unpackaged symbol to a packaged symbol exists.
The package object also supports an 'sref operation:
(sref ob v k)
k is an unpackaged symbol while v is a packaged symbol; the implementation is free to throw an error if this invariant is violated.
Packages are handled by interface.
Further, we also predefine two packages, axiom and arc.
The axiom package is implicitly imported into all packages. It presents no interface
The arc package contains all "standard" Arc functions and macros. The arc package is not implicitly imported into all packages.
The arc package contains the interface arc::v3 . This interface is the set of symbols currently defined on Anarki. Future extensions to the arc standard library must be first placed in the interface arc::v3-exp until they are placed into a future arc::v4 interface, and so on.
load
====
The load implementation is thus:
(def load (file (o hook))
" Reads the expressions in `file' and evaluates them. Read expressions
may be preprocessed by `hook'.
See also [[require]]. "
(push current-load-file* load-file-stack*)
(= current-load-file* file)
(or= hook idfn)
(after
(w/infile f file
(let evaller (eval-cxt)
(evaller '(in-package User))
(whilet e (read f)
(evaller (hook e)))))
(do (= current-load-file* (pop load-file-stack*)) nil)))
