mirror of
https://github.com/michaelcmartin/Ophis.git
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208 lines
3.3 KiB
HTML
208 lines
3.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<HTML
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><HEAD
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><TITLE
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>Labels and aliases</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
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REL="HOME"
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TITLE="Programming with Ophis"
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HREF="book1.html"><LINK
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REL="PREVIOUS"
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TITLE="Assembling the code"
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HREF="x149.html"><LINK
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REL="NEXT"
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TITLE="Anonymous labels"
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HREF="x214.html"></HEAD
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><BODY
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CLASS="CHAPTER"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Programming with Ophis</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="x149.html"
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ACCESSKEY="P"
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><<< Previous</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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></TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="x214.html"
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ACCESSKEY="N"
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>Next >>></A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="AEN200"
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></A
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>Labels and aliases</H1
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><P
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> Labels are an important part of your code. However, since each
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label must normally be unique, this can lead to <SPAN
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CLASS="QUOTE"
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>"namespace
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pollution,"</SPAN
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> and you'll find yourself going through ever
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more contorted constructions to generate unique label names.
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Ophis offers two solutions to this: <I
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CLASS="EMPHASIS"
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>anonymous
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labels</I
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> and <I
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CLASS="EMPHASIS"
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>temporary labels</I
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>. This
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tutorial will cover both of these facilities, and also introduce
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the aliasing mechanism.
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</P
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><DIV
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CLASS="SECTION"
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><H1
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CLASS="SECTION"
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><A
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NAME="AEN206"
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>Temporary labels</A
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></H1
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><P
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> Temporary labels are the easiest to use. If a label begins with
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an underscore, it will only be reachable from inside the
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innermost enclosing scope. Scopes begin when
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a <TT
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CLASS="LITERAL"
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>.scope</TT
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> statement is encountered. This
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produces a new, inner scope if there is another scope in use.
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The <TT
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CLASS="LITERAL"
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>.scend</TT
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> command ends the innermost
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currently active scope.
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</P
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><P
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> We can thus rewrite our header data using temporary labels, thus
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allowing the main program to have a label
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named <TT
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CLASS="LITERAL"
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>next</TT
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> if it wants.
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</P
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><TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>.word $0801
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.org $0801
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.scope
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.word _next, 10 ; Next line and current line number
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.byte $9e," 2064",0 ; SYS 2064
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_next: .word 0 ; End of program
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.scend
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.advance 2064</PRE
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></TD
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></TR
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></TABLE
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></DIV
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="x149.html"
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ACCESSKEY="P"
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><<< Previous</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="book1.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="x214.html"
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ACCESSKEY="N"
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>Next >>></A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Assembling the code</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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> </TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Anonymous labels</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |