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/* xljump - execution context routines */
/* Copyright (c) 1985, by David Michael Betz
All Rights Reserved
Permission is granted for unrestricted non-commercial use */
#include "xlisp.h"
/* external variables */
extern XLCONTEXT *xlcontext,*xltarget;
extern LVAL xlvalue,xlenv,xlfenv,xldenv;
extern int xlmask;
LOCAL void findandjump(int mask, const char *error);
/* xlbegin - beginning of an execution context */
void xlbegin(XLCONTEXT *cptr, int flags, LVAL expr)
{
cptr->c_flags = flags;
cptr->c_expr = expr;
cptr->c_xlstack = xlstack;
cptr->c_xlenv = xlenv;
cptr->c_xlfenv = xlfenv;
cptr->c_xldenv = xldenv;
cptr->c_xlcontext = xlcontext;
cptr->c_xlargv = xlargv;
cptr->c_xlargc = xlargc;
cptr->c_xlfp = xlfp;
cptr->c_xlsp = xlsp;
xlcontext = cptr;
}
/* xlend - end of an execution context */
void xlend(XLCONTEXT *cptr)
{
xlcontext = cptr->c_xlcontext;
}
/* xlgo - go to a label */
void xlgo(LVAL label)
{
XLCONTEXT *cptr;
LVAL *argv;
int argc;
/* find a tagbody context */
for (cptr = xlcontext; cptr; cptr = cptr->c_xlcontext)
if (cptr->c_flags & CF_GO) {
argc = cptr->c_xlargc;
argv = cptr->c_xlargv;
while (--argc >= 0)
if (*argv++ == label) {
cptr->c_xlargc = argc;
cptr->c_xlargv = argv;
xljump(cptr,CF_GO,NIL);
}
}
xlfail("no target for GO");
}
/* xlreturn - return from a block */
void xlreturn(LVAL name, LVAL val)
{
XLCONTEXT *cptr;
/* find a block context */
for (cptr = xlcontext; cptr; cptr = cptr->c_xlcontext)
if (cptr->c_flags & CF_RETURN && cptr->c_expr == name)
xljump(cptr,CF_RETURN,val);
xlfail("no target for RETURN");
}
/* xlthrow - throw to a catch */
void xlthrow(LVAL tag, LVAL val)
{
XLCONTEXT *cptr;
/* find a catch context */
for (cptr = xlcontext; cptr; cptr = cptr->c_xlcontext)
if ((cptr->c_flags & CF_THROW) && cptr->c_expr == tag)
xljump(cptr,CF_THROW,val);
xlfail("no target for THROW");
}
/* xlsignal - signal an error */
void xlsignal(const char *emsg, LVAL arg)
{
XLCONTEXT *cptr;
/* find an error catcher */
for (cptr = xlcontext; cptr; cptr = cptr->c_xlcontext)
if (cptr->c_flags & CF_ERROR) {
if (cptr->c_expr && emsg)
xlerrprint("error",NULL,emsg,arg);
xljump(cptr,CF_ERROR,NIL);
}
}
/* xltoplevel - go back to the top level */
void xltoplevel(void)
{
close_loadingfiles();
stdputstr("[ back to top level ]\n");
findandjump(CF_TOPLEVEL,"no top level");
}
/* xlbrklevel - go back to the previous break level */
void xlbrklevel(void)
{
findandjump(CF_BRKLEVEL,"no previous break level");
}
/* xlcleanup - clean-up after an error */
void xlcleanup(void)
{
stdputstr("[ back to previous break level ]\n");
findandjump(CF_CLEANUP,"not in a break loop");
}
/* xlcontinue - continue from an error */
void xlcontinue(void)
{
findandjump(CF_CONTINUE,"not in a break loop");
}
/* xljump - jump to a saved execution context */
void xljump(XLCONTEXT *target, int mask, LVAL val)
{
/* unwind the execution stack */
for (; xlcontext != target; xlcontext = xlcontext->c_xlcontext)
/* check for an UNWIND-PROTECT */
if ((xlcontext->c_flags & CF_UNWIND)) {
xltarget = target;
xlmask = mask;
break;
}
/* restore the state */
xlstack = xlcontext->c_xlstack;
xlenv = xlcontext->c_xlenv;
xlfenv = xlcontext->c_xlfenv;
xlunbind(xlcontext->c_xldenv);
xlargv = xlcontext->c_xlargv;
xlargc = xlcontext->c_xlargc;
xlfp = xlcontext->c_xlfp;
xlsp = xlcontext->c_xlsp;
xlvalue = val;
/* call the handler */
_longjmp(xlcontext->c_jmpbuf,mask);
}
/* findandjump - find a target context frame and jump to it */
LOCAL void findandjump(int mask, const char *error)
{
XLCONTEXT *cptr;
/* find a block context */
for (cptr = xlcontext; cptr; cptr = cptr->c_xlcontext)
if (cptr->c_flags & mask)
xljump(cptr,mask,NIL);
xlabort(error);
}
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