289 lines
4.8 KiB
HTML
289 lines
4.8 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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>Macros</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="UP"
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TITLE="Headers, Libraries, and Macros"
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REL="PREVIOUS"
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TITLE="Headers, Libraries, and Macros"
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HREF="c236.html"><LINK
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REL="NEXT"
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TITLE="Example code"
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HREF="x287.html"></HEAD
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><BODY
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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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><<< 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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>Headers, Libraries, and Macros</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="x287.html"
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ACCESSKEY="N"
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>Next >>></A
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></TD
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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="SECTION"
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><H1
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CLASS="SECTION"
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><A
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NAME="AEN257"
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>Macros</A
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></H1
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><P
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> A macro is a way of expressing a lot of code or data with a
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simple shorthand. It's also usually configurable. Traditional
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macro systems such as C's <TT
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CLASS="LITERAL"
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>#define</TT
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> mechanic
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use <I
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CLASS="EMPHASIS"
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>textual replacement</I
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>: a macro is
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expanded before any evaluation or even parsing occurs.
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</P
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><P
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> In contrast, Ophis's macro system uses a <I
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CLASS="EMPHASIS"
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>call by
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value</I
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> approach where the arguments to macros are
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evaluated to bytes or words before being inserted into the macro
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body. This produces effects much closer to those of a
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traditional function call. A more detailed discussion of the
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tradeoffs may be found in <A
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HREF="a505.html"
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>the Appendix called <I
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>Ophis Command Reference</I
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></A
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>.
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</P
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><DIV
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CLASS="SECTION"
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><H2
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CLASS="SECTION"
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><A
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NAME="AEN265"
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>Macro definitions</A
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></H2
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><P
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> A macro definition is a set of statements between
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a <TT
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CLASS="LITERAL"
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>.macro</TT
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> statement and
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a <TT
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CLASS="LITERAL"
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>.macend</TT
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> statement.
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The <TT
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CLASS="LITERAL"
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>.macro</TT
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> statement also names the macro
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being defined.
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</P
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><P
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> No global or anonymous labels may be defined inside a macro:
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temporary labels only persist in the macro expansion itself.
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(Each macro body has its own scope.)
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</P
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><P
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> Arguments to macros are referred to by number: the first is
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<TT
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CLASS="LITERAL"
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>_1</TT
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>, the second <TT
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CLASS="LITERAL"
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>_2</TT
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>, and so on.
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</P
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><P
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> Here's a macro that encapsulates the printing routine in our
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<SPAN
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CLASS="QUOTE"
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>"Hello World"</SPAN
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> program, with an argument being the
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address of the string to print:
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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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>.macro print
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ldx #0
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_loop: lda _1, x
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beq _done
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jsr chrout
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inx
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bne _loop
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_done:
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.macend</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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CLASS="SECTION"
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><H2
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CLASS="SECTION"
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><A
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NAME="AEN278"
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>Macro invocations</A
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></H2
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><P
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> Macros may be invoked in two ways: one that looks like a
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directive, and one that looks like an instruction.
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</P
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><P
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> The most common way to invoke a macro is to backquote the name
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of the macro. It is also possible to use
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the <TT
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CLASS="LITERAL"
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>.invoke</TT
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> command. These commands look
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like this:
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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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>`print msg
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.invoke print msg</PRE
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></TD
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></TR
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></TABLE
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><P
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> Arguments are passed to the macro as a comma-separated list.
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They must all be expressions that evaluate to byte or word
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values—a mechanism similar to <TT
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CLASS="LITERAL"
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>.alias</TT
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>
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is used to assign their values to the <TT
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CLASS="LITERAL"
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>_n</TT
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>
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names.
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</P
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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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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="c236.html"
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ACCESSKEY="P"
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><<< Previous</A
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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HREF="book1.html"
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>Home</A
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HREF="x287.html"
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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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>Headers, Libraries, and Macros</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="c236.html"
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>Up</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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>Example code</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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> |