mirror of
https://github.com/michaelcmartin/Ophis.git
synced 2024-06-27 10:29:31 +00:00
221 lines
3.7 KiB
HTML
221 lines
3.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>Labels and aliases</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
|
|
REL="HOME"
|
|
TITLE="Programming with Ophis"
|
|
HREF="book1.html"><LINK
|
|
REL="UP"
|
|
TITLE="Using the Ophis Assembler"
|
|
HREF="p51.html"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="Assembling the code"
|
|
HREF="x171.html"><LINK
|
|
REL="NEXT"
|
|
TITLE="Anonymous labels"
|
|
HREF="x251.html"></HEAD
|
|
><BODY
|
|
CLASS="CHAPTER"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>Programming with Ophis</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x171.html"
|
|
ACCESSKEY="P"
|
|
><<< Previous</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
></TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x251.html"
|
|
ACCESSKEY="N"
|
|
>Next >>></A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="CHAPTER"
|
|
><H1
|
|
><A
|
|
NAME="AEN236"
|
|
></A
|
|
>Labels and aliases</H1
|
|
><P
|
|
> Labels are an important part of your code. However, since each
|
|
label must normally be unique, this can lead to <SPAN
|
|
CLASS="QUOTE"
|
|
>"namespace
|
|
pollution,"</SPAN
|
|
> and you'll find yourself going through ever
|
|
more contorted constructions to generate unique label names.
|
|
Ophis offers two solutions to this: <I
|
|
CLASS="EMPHASIS"
|
|
>anonymous
|
|
labels</I
|
|
> and <I
|
|
CLASS="EMPHASIS"
|
|
>temporary labels</I
|
|
>. This
|
|
tutorial will cover both of these facilities, and also introduce
|
|
the aliasing mechanism.
|
|
</P
|
|
><DIV
|
|
CLASS="SECTION"
|
|
><H1
|
|
CLASS="SECTION"
|
|
><A
|
|
NAME="AEN242"
|
|
>Temporary labels</A
|
|
></H1
|
|
><P
|
|
> Temporary labels are the easiest to use. If a label begins with
|
|
an underscore, it will only be reachable from inside the
|
|
innermost enclosing scope. Scopes begin when
|
|
a <TT
|
|
CLASS="LITERAL"
|
|
>.scope</TT
|
|
> statement is encountered. This
|
|
produces a new, inner scope if there is another scope in use.
|
|
The <TT
|
|
CLASS="LITERAL"
|
|
>.scend</TT
|
|
> command ends the innermost
|
|
currently active scope.
|
|
</P
|
|
><P
|
|
> We can thus rewrite our header data using temporary labels, thus
|
|
allowing the main program to have a label
|
|
named <TT
|
|
CLASS="LITERAL"
|
|
>next</TT
|
|
> if it wants.
|
|
</P
|
|
><TABLE
|
|
BORDER="0"
|
|
BGCOLOR="#E0E0E0"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
><PRE
|
|
CLASS="PROGRAMLISTING"
|
|
>.word $0801
|
|
.org $0801
|
|
|
|
.scope
|
|
.word _next, 10 ; Next line and current line number
|
|
.byte $9e," 2064",0 ; SYS 2064
|
|
_next: .word 0 ; End of program
|
|
.scend
|
|
|
|
.advance 2064</PRE
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><P
|
|
> It's possible to have multiple temporary labels with the same
|
|
name in different parts of the code. If you create a label map
|
|
in those cases, you will have to look at the sourcefile location
|
|
to distinguish them.
|
|
</P
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x171.html"
|
|
ACCESSKEY="P"
|
|
><<< Previous</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="book1.html"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x251.html"
|
|
ACCESSKEY="N"
|
|
>Next >>></A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Assembling the code</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="p51.html"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Anonymous labels</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |