xljump.c

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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, 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(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, 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);
}