ref: 42be27517c8057733afe2d31b8bf7b98ee6f6578
dir: /eval.c/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include "dat.h"
#include "fns.h"
int equalterms(Term *, Term *);
Goal *copygoals(Goal *);
Builtin findbuiltin(Term *);
void addchoicepoints(Clause *, Term *, Goal *, Module *);
int
evalquery(Term *query)
{
Binding *replbindings = nil;
goalstack = addgoals(goalstack, query, usermodule);
while(goalstack->goal != nil){
Term *goal = goalstack->goal;
Term *catcher = goalstack->catcher;
Module *module = goalstack->module;
goalstack = goalstack->next;
if(catcher)
continue;
if(flagdebug)
print("Working goal: %S:%S\n", module->name, prettyprint(goal, 0, 0, 0, nil));
Binding *bindings = nil;
Clause *clause = nil;
/* Try to see if the goal can be solved using a builtin first */
Builtin builtin = findbuiltin(goal);
if(builtin != nil){
int success = builtin(goal, &bindings, module);
if(!success)
goto Backtrack;
}else{
Predicate *pred = findpredicate(module->predicates, goal);
if(pred == nil){
Rune *name;
int arity;
Term *replacement = nil;
Term *procedure;
Term *pi;
if(goal->tag == CompoundTerm){
name = goal->text;
arity = goal->arity;
}else{
name = prettyprint(goal, 0, 0, 0, nil);
arity = 0;
}
switch(flagunknown){
case UnknownError:
procedure = mkatom(name);
procedure->next = mkinteger(arity);
pi = mkcompound(L"/", 2, procedure);
replacement = existenceerror(L"procedure", pi);
break;
case UnknownWarning:
print("Warning: no such predicate in module %S: %S/%d\n", module->name, name, arity);
case UnknownFail:
replacement = mkatom(L"fail");
}
goalstack = addgoals(goalstack, replacement, module);
continue;
}
/* Find a clause where the head unifies with the goal */
clause = findclause(pred->clauses, goal, &bindings);
if(clause != nil)
addchoicepoints(clause, goal, goalstack, module);
else{
Backtrack:
if(choicestack == nil)
return 0;
if(flagdebug)
print("Backtracking..\n");
Choicepoint *cp = choicestack;
choicestack = cp->next;
goalstack = cp->goalstack;
module = cp->currentmodule;
clause = cp->alternative;
bindings = cp->altbindings;
}
}
/* Apply bindings to all goals on the stack except catchframes */
Goal *g;
for(g = goalstack; g != nil; g = g->next){
if(g->goal != nil && g->catcher == nil)
applybinding(g->goal, bindings);
}
/* Add clause body as goals, with bindings applied */
if(clause != nil && clause->body != nil){
Term *subgoal = copyterm(clause->body, nil);
applybinding(subgoal, bindings);
goalstack = addgoals(goalstack, subgoal, module);
}
}
goalstack = goalstack->next;
unify(query, goalstack->goal, &replbindings);
return 1;
}
Goal *
addgoals(Goal *goals, Term *t, Module *module)
{
if(t->tag == CompoundTerm && runestrcmp(t->text, L",") == 0 && t->arity == 2){
goals = addgoals(goals, t->children->next, module);
goals = addgoals(goals, t->children, module);
}else{
if(t->tag == CompoundTerm && runestrcmp(t->text, L":") == 0 && t->arity == 2){
Term *moduleterm = t->children;
if(moduleterm->tag == AtomTerm){
Module *m = getmodule(moduleterm->text);
if(m == nil)
t = existenceerror(L"module", moduleterm);
else{
t = moduleterm->next;
module = m;
}
}else
t = typeerror(L"module", moduleterm);
}
Goal *g = gmalloc(sizeof(Goal));
g->goal = t;
g->module = module;
g->catcher = nil;
g->next = goals;
goals = g;
}
return goals;
}
Clause *
findclause(Clause *clauses, Term *goal, Binding **bindings)
{
Clause *clause;
for(; clauses != nil; clauses = clauses->next){
clause = copyclause(clauses, &clausenr);
clausenr++;
clause->next = clauses->next;
if(unify(clause->head, goal, bindings))
return clause;
}
return nil;
}
Predicate *
findpredicate(Predicate *preds, Term *goal)
{
Rune *name;
int arity;
name = goal->text;
if(goal->tag == AtomTerm)
arity = 0;
else
arity = goal->arity;
Predicate *p;
for(p = preds; p != nil; p = p->next){
if(runestrcmp(p->name, name) == 0 && p->arity == arity)
return p;
}
return nil;
}
int
unify(Term *a, Term *b, Binding **bindings)
{
Term *leftstack;
Term *rightstack;
Term *left;
Term *right;
leftstack = copyterm(a, nil);
rightstack = copyterm(b, nil);
while(leftstack != nil && rightstack != nil){
left = leftstack;
leftstack = left->next;
right = rightstack;
rightstack = right->next;
if(equalterms(left, right))
continue;
else if(left->tag == VariableTerm || right->tag == VariableTerm){
if(left->tag != VariableTerm && right->tag == VariableTerm){
Term *tmp = left;
left = right;
right = tmp;
}
if(left->tag == VariableTerm && right->tag == VariableTerm && right->clausenr > left->clausenr){
Term *tmp = left;
left = right;
right = tmp;
}
if(runestrcmp(left->text, L"_") == 0)
continue; /* _ doesn't introduce a new binding */
Binding *b = gmalloc(sizeof(Binding));
b->name = left->text;
b->nr = left->clausenr;
b->value = right;
b->next = *bindings;
*bindings = b;
Term *t;
for(t = leftstack; t != nil; t = t->next)
applybinding(t, b);
for(t = rightstack; t != nil; t = t->next)
applybinding(t, b);
Binding *tmpb;
for(tmpb = *bindings; tmpb != nil; tmpb = tmpb->next)
applybinding(tmpb->value, b);
}else if(left->tag == CompoundTerm && right->tag == CompoundTerm && left->arity == right->arity && runestrcmp(left->text, right->text) == 0){
Term *leftchild = left->children;
Term *rightchild = right->children;
while(leftchild != nil && rightchild != nil){
Term *t1 = copyterm(leftchild, nil);
t1->next = leftstack;
leftstack = t1;
leftchild = leftchild->next;
Term *t2 = copyterm(rightchild, nil);
t2->next = rightstack;
rightstack = t2;
rightchild = rightchild->next;
}
}else{
*bindings = nil;
return 0; /* failure */
}
}
return 1;
}
int
equalterms(Term *a, Term *b)
{
/* Check that two non-compound terms are identical */
if(a->tag != b->tag)
return 0;
switch(a->tag){
case AtomTerm:
return runestrcmp(a->text, b->text) == 0;
case VariableTerm:
return (runestrcmp(a->text, b->text) == 0 && a->clausenr == b->clausenr);
case FloatTerm:
return a->dval == b->dval;
case IntegerTerm:
return a->ival == b->ival;
default:
return 0;
}
}
void
applybinding(Term *t, Binding *bindings)
{
if(t->tag == VariableTerm){
Binding *b;
for(b = bindings; b != nil; b = b->next){
if(runestrcmp(t->text, b->name) == 0 && t->clausenr == b->nr){
Term *next = t->next;
memcpy(t, b->value, sizeof(Term));
t->next = next;
return;
}
}
}else if(t->tag == CompoundTerm){
Term *child;
for(child = t->children; child != nil; child = child->next)
applybinding(child, bindings);
}
}
Goal *
copygoals(Goal *goals)
{
if(goals != nil){
Goal *g = gmalloc(sizeof(Goal));
g->module = goals->module;
if(goals->goal)
g->goal = copyterm(goals->goal, nil);
else
g->goal = nil;
if(goals->catcher)
g->catcher = copyterm(goals->catcher, nil);
else
g->catcher = nil;
g->next = copygoals(goals->next);
return g;
}else
return nil;
}
void
addchoicepoints(Clause *clause, Term *goal, Goal *goals, Module *mod){
/* Find all alternative clauses that would have matched, and create a choicepoint for them */
Choicepoint *cps = nil;
Choicepoint *last = nil;
Clause *alt = clause->next;
while(alt != nil){
Binding *altbindings = nil;
clause = findclause(alt, goal, &altbindings);
if(clause){
/* Add choicepoint here */
Choicepoint *cp = gmalloc(sizeof(Choicepoint));
cp->goalstack = copygoals(goals);
cp->next = nil;
cp->alternative = clause;
cp->altbindings = altbindings;
cp->id = clause->clausenr;
cp->currentmodule = mod;
if(cps == nil){
cps = cp;
last = cp;
}else{
last->next = cp;
last = cp;
}
alt = clause->next;
}else
alt = nil;
}
if(last){
last->next = choicestack;
choicestack = cps;
}
}