108 lines
3.6 KiB
C
108 lines
3.6 KiB
C
/**
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* intern.c
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*
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* For now this implements an oblist and shallow binding; local environments can
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* be consed onto the front of the oblist. Later, this won't do; bindings will happen
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* in namespaces, which will probably be implemented as hash tables.
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*
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* Doctrine is that cons cells are immutable, and life is a lot more simple if they are;
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* so when a symbol is rebound in the master oblist, what in fact we do is construct
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* a new oblist without the previous binding but with the new binding. Anything which,
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* prior to this action, held a pointer to the old oblist (as all current threads'
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* environments must do) continues to hold a pointer to the old oblist, and consequently
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* doesn't see the change. This is probably good but does mean you cannot use bindings
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* on the oblist to signal between threads.
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*
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* (c) 2017 Simon Brooke <simon@journeyman.cc>
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* Licensed under GPL version 2.0, or, at your option, any later version.
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*/
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#include <stdbool.h>
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#include "equal.h"
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#include "conspage.h"
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#include "consspaceobject.h"
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/**
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* The object list. What is added to this during system setup is 'global', that is,
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* visible to all sessions/threads. What is added during a session/thread is local to
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* that session/thread (because shallow binding). There must be some way for a user to
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* make the contents of their own environment persistent between threads but I don't
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* know what it is yet. At some stage there must be a way to rebind deep values so
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* they're visible to all users/threads, but again I don't yet have any idea how
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* that will work.
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*/
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struct cons_pointer oblist = NIL;
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/**
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* return the value associated with this key in this store. In the current
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* implementation a store is just an assoc list, but in future it might be a
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* namespace, a regularity or a homogeneity.
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* TODO: This function ultimately belongs in lispops.
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*/
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struct cons_pointer assoc( struct cons_pointer key, struct cons_pointer store) {
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struct cons_pointer result = NIL;
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if ( consp( store)) {
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struct cons_space_object* cell_store = &pointer2cell( store);
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if ( consp( cell_store->payload.cons.car)) {
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struct cons_space_object* binding =
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&pointer2cell( cell_store->payload.cons.car);
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if ( eq( key, binding->payload.cons.car)) {
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result = binding->payload.cons.cdr;
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}
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}
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/* top-level objects on an assoc list ought to be conses (i.e. each
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* successive car should be a cons), but there's no need to throw a
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* wobbly if it isn't. */
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if ( nilp( result)) {
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result = assoc( key, cell_store->payload.cons.cdr);
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}
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}
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return result;
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}
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/**
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* Return true if this key is present as a key in this enviroment, defaulting to
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* the oblist if no environment is passed.
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*/
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bool internedp( struct cons_pointer key, struct cons_pointer environment) {
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bool result = false;
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if ( nilp( environment)) {
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if ( !nilp( oblist)) {
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result = internedp( key, oblist);
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}
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} else {
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result = !nilp( assoc( key, environment));
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}
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return result;
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}
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/**
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* Return a new key/value store containing all the key/value pairs in this store
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* with this key/value pair added to the front.
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*/
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struct cons_pointer bind( struct cons_pointer key, struct cons_pointer value,
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struct cons_pointer store) {
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return make_cons( make_cons( key, value), store);
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}
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/**
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* Binds this key to this value in the global oblist, but doesn't affect the
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* current environment. May not be useful except in bootstrapping (and even
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* there it may not be especially useful).
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*/
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struct cons_pointer deep_bind( struct cons_pointer key, struct cons_pointer value) {
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oblist = bind( key, value, oblist);
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return oblist;
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}
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