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>Assembler directives</TITLE
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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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><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="AEN1261"
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>Assembler directives</A
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></H1
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><P
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> Assembler directives are all instructions to the assembler
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that are not actual instructions. Ophis's set of directives
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follow.
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</P
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><P
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></P
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><UL
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.outfile</TT
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> <I
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CLASS="EMPHASIS"
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>filename</I
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>:
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Sets the filename for the output binary if one has not
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already been set. If no name is ever set, the output will
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be written to <TT
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CLASS="LITERAL"
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>ophis.bin</TT
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>.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.advance</TT
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> <I
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CLASS="EMPHASIS"
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>address</I
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>
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[, <I
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CLASS="EMPHASIS"
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>filler</I
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>]: Forces the program
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counter to be <I
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CLASS="EMPHASIS"
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>address</I
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>. Unlike
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the <TT
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CLASS="LITERAL"
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>.org</TT
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>
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directive, <TT
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CLASS="LITERAL"
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>.advance</TT
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> outputs bytes (the
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value of <I
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CLASS="EMPHASIS"
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>filler</I
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>, or zeroes if it is
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unspecified) until the program counter reaches a
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specified address. Attempting
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to <TT
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CLASS="LITERAL"
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>.advance</TT
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> to a point behind the
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current program counter is an assemble-time error.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.alias</TT
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> <I
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CLASS="EMPHASIS"
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>label</I
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> <I
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CLASS="EMPHASIS"
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>value</I
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>:
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The .alias directive assigns an arbitrary value to a
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label. This value may be an arbitrary argument, but
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cannot reference any label that has not already been
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defined (this prevents recursive label
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dependencies).
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.byte</TT
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> <I
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CLASS="EMPHASIS"
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>arg</I
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> [
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, <I
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CLASS="EMPHASIS"
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>arg</I
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>, ... ]: Specifies a series of
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arguments, which are evaluated, and strings, which are
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included as raw ASCII data. The final results of these
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arguments must be one byte in size. Seperate constants
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are seperated by comments.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.checkpc</TT
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> <I
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CLASS="EMPHASIS"
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>address</I
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>:
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Ensures that the program counter is less than or equal to
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the address specified, and emits an assemble-time error
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if it is not. <I
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CLASS="EMPHASIS"
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>This produces no code in the
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final binary - it is there to ensure that linking a large
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amount of data together does not overstep memory
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boundaries.</I
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>
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.data</TT
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> <I
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CLASS="EMPHASIS"
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>[label]</I
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>:
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Sets the segment to the segment name specified and
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disallows output. If no label is given, switches to the
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default data segment.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.incbin</TT
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> <I
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CLASS="EMPHASIS"
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>filename</I
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>
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[, <I
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CLASS="EMPHASIS"
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>offset</I
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>
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[, <I
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CLASS="EMPHASIS"
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>length</I
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>]]: Inserts the contents of
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the file specified as binary data. Use it to include
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graphics information, precompiled code, or other
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non-assembler data. You may also optionally specify an
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index to start including from, or a length to only
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include a subset.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.include</TT
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> <I
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CLASS="EMPHASIS"
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>filename</I
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>:
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Includes the entirety of the file specified at that point
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in the program. Use this to order your final sources, if
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you aren't doing it via the command line.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.org</TT
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> <I
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CLASS="EMPHASIS"
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>address</I
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>:
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Sets the program counter to the address
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specified. <I
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CLASS="EMPHASIS"
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>This does not emit any code in and
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of itself, nor does it overwrite anything that previously
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existed.</I
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> If you wish to jump ahead in memory,
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use <TT
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CLASS="LITERAL"
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>.advance</TT
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>.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.require</TT
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> <I
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CLASS="EMPHASIS"
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>filename</I
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>:
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Includes the entirety of the file specified at that point
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in the program. Unlike <TT
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CLASS="LITERAL"
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>.include</TT
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>,
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however, code included with <TT
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CLASS="LITERAL"
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>.require</TT
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>
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will only be inserted once.
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The <TT
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CLASS="LITERAL"
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>.require</TT
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> directive is useful for
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ensuring that certain code libraries are somewhere in the
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final binary. They are also very useful for guaranteeing
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that macro libraries are available.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.space</TT
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> <I
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CLASS="EMPHASIS"
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>label</I
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> <I
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CLASS="EMPHASIS"
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>size</I
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>:
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This directive is used to organize global variables. It
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defines the label specified to be at the current location
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of the program counter, and then advances the program
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counter <I
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CLASS="EMPHASIS"
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>size</I
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> steps ahead. No actual
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code is produced. This is equivalent to <TT
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CLASS="LITERAL"
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>label:
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.org ^+size</TT
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>.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.text</TT
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> <I
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CLASS="EMPHASIS"
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>[label]</I
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>:
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Sets the segment to the segment name specified and allows
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output. If no label is given, switches to the default
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text segment.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.word</TT
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> <I
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CLASS="EMPHASIS"
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>arg</I
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> [
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, <I
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CLASS="EMPHASIS"
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>arg</I
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>, ... ]:
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Like <TT
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CLASS="LITERAL"
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>.byte</TT
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>, but values are all treated
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as two-byte values and stored low-end first (as is the
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6502's wont). Use this to create jump tables (an
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unadorned label will evaluate to that label's location)
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or otherwise store 16-bit data.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.dword</TT
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> <I
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CLASS="EMPHASIS"
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>arg</I
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> [
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, <I
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CLASS="EMPHASIS"
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>arg</I
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>, ...]:
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Like <TT
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CLASS="LITERAL"
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>.word</TT
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>, but for 32-bit
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values.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.wordbe</TT
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> <I
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CLASS="EMPHASIS"
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>arg</I
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> [
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, <I
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CLASS="EMPHASIS"
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>arg</I
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>, ...]:
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Like <TT
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CLASS="LITERAL"
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>.word</TT
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>, but stores the value in a
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big-endian format (high byte first).
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.dwordbe</TT
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> <I
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CLASS="EMPHASIS"
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>arg</I
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> [
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, <I
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CLASS="EMPHASIS"
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>arg</I
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>, ...]:
|
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Like <TT
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CLASS="LITERAL"
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>.dword</TT
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>, but stores the value high
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byte first.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.scope</TT
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>: Starts a new scope
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block. Labels that begin with an underscore are only
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reachable from within their innermost
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enclosing <TT
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CLASS="LITERAL"
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>.scope</TT
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>
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statement.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.scend</TT
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>: Ends a scope block. Makes the
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temporary labels defined since the
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last <TT
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CLASS="LITERAL"
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>.scope</TT
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> statement unreachable, and
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permits them to be redefined in a new
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scope.
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.macro</TT
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> <I
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CLASS="EMPHASIS"
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>name</I
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>:
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Begins a macro definition block. This is a scope block
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that can be inlined at arbitrary points
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with <TT
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CLASS="LITERAL"
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>.invoke</TT
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>. Arguments to the macro
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will be bound to temporary labels with names like
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<TT
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CLASS="LITERAL"
|
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>_1</TT
|
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>, <TT
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CLASS="LITERAL"
|
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>_2</TT
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>, etc.
|
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</P
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></LI
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.macend</TT
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>: Ends a macro definition block.
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</P
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></LI
|
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><LI
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><P
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> <TT
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CLASS="LITERAL"
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>.invoke</TT
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> <I
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CLASS="EMPHASIS"
|
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>label</I
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> [<I
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CLASS="EMPHASIS"
|
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>argument</I
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> [,
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<I
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CLASS="EMPHASIS"
|
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>argument</I
|
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> ...]]: invokes (inlines) the
|
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specified macro, binding the values of the arguments to the
|
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ones the macro definition intends to read. A shorthand
|
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for <TT
|
|
CLASS="LITERAL"
|
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>.invoke</TT
|
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> is the name of the macro to
|
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invoke, backquoted.
|
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</P
|
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></LI
|
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></UL
|
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|
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