Ubuntu Manpage: grammar::me::cpu::gasm

NAME

       grammar::me::cpu::gasm - ME assembler

SYNOPSIS

       package require grammar::me::cpu::gasm  ?0.1?

       ::grammar::me::cpu::gasm::begin g n ?mode? ?note?

       ::grammar::me::cpu::gasm::done --> t

       ::grammar::me::cpu::gasm::state

       ::grammar::me::cpu::gasm::state! s

       ::grammar::me::cpu::gasm::lift t dst = src

       ::grammar::me::cpu::gasm::Inline t node label

       ::grammar::me::cpu::gasm::Cmd cmd ?arg...?

       ::grammar::me::cpu::gasm::Bra

       ::grammar::me::cpu::gasm::Nop text

       ::grammar::me::cpu::gasm::Note text

       ::grammar::me::cpu::gasm::Jmp label

       ::grammar::me::cpu::gasm::Exit

       ::grammar::me::cpu::gasm::Who label

       ::grammar::me::cpu::gasm::/Label name

       ::grammar::me::cpu::gasm::/Clear

       ::grammar::me::cpu::gasm::/Ok

       ::grammar::me::cpu::gasm::/Fail

       ::grammar::me::cpu::gasm::/At name

       ::grammar::me::cpu::gasm::/CloseLoop

_________________________________________________________________________________________________

DESCRIPTION

       This  package  provides  a  simple  in-memory  assembler.  Its origin is that of a support
       package for use by packages converting PEG and other grammars into a corresponding matcher
       based  on  the  ME  virtual  machine,  like page::compiler::peg::mecpu. Despite that it is
       actually mostly agnostic regarding the instructions, users can choose any instruction  set
       they like.

       The  program  under  construction is held in a graph structure (See package struct::graph)
       during assembly and subsequent manipulation, with instructions represented by  nodes,  and
       the flow of execution between instructions explicitly encoded in the arcs between them.

       In  this  model  jumps  are  not  encoded  explicitly,  they are implicit in the arcs. The
       generation of explicit jumps is left to any code converting the  graph  structure  into  a
       more  conventional representation. The same goes for branches. They are implicitly encoded
       by all instructions which have two outgoing arcs, whereas all other instructions have only
       one  outgoing  arc.  Their  conditonality  is  handled by tagging their outgoing arcs with
       information about the conditions under which they are taken.

       While the graph the assembler operates on is supplied from the outside, i.e. external,  it
       does manage some internal state, namely:

       [1]    The handle of the graph node most assembler operations will work on, the anchor.

       [2]    A  mapping  from arbitrary strings to instructions. I.e. it is possible to label an
              instruction during assembly, and later recall that instruction by its label.

       [3]    The condition code to use when creating arcs between instructions, which is one  of
              always, ok, and fail.

       [4]    The current operation mode, one of halt, okfail, and !okfail.

       [5]    The name of a node in a tree. This, and the operation mode above are the parts most
              heavily influenced by the needs of a grammar compiler, as they  assume  some  basic
              program  structures (selected through the operation mode), and intertwine the graph
              with a tree, like the AST for the grammar to be compiled.

DEFINITIONS

As the graph the assembler is operating on, and the tree it is intertwined with, are
supplied to the assembler from the outside it is necessary to specify the API expected
from them, and to describe the structures expected and/or generated by the assembler in
either.

[1] Any graph object command used by the assembler has to provide the API as specified
in the documentation for the package struct::graph.

[2] Any tree object command used by the assembler has to provide the API as specified
in the documentation for the package struct::tree.

[3] Any instruction (node) generated by the assembler in a graph will have at least
two, and at most three attributes:

instruction
The value of this attribute is the name of the instruction. The only names
currently defined by the assembler are the three pseudo-instructions

NOP This instruction does nothing. Useful for fixed framework nodes,
unchanging jump destinations, and the like. No arguments.

C A .NOP to allow the insertion of arbitrary comments into the
instruction stream, i.e. a comment node. One argument, the text of
the comment.

BRA A .NOP serving as explicitly coded conditional branch. No arguments.

However we reserve the space of all instructions whose names begin with a
"." (dot) for future use by the assembler.

arguments
The value of this attribute is a list of strings, the arguments of the
instruction. The contents are dependent on the actual instruction and the
assembler doesn't know or care about them. This means for example that it
has no builtin knowledge about what instruction need which arguments and
thus doesn't perform any type of checking.

expr This attribute is optional. When it is present its value is the name of a
node in the tree intertwined with the graph.

[4] Any arc between two instructions will have one attribute:

condition
The value of this attribute determines under which condition execution will
take this arc. It is one of always, ok, and fail. The first condition is
used for all arcs which are the single outgoing arc of an instruction. The
other two are used for the two outgoing arcs of an instruction which
implicitly encode a branch.

[5] A tree node given to the assembler for cross-referencing will be written to and
given the following attributes, some fixed, some dependent on the operation mode.
All values will be references to nodes in the instruction graph. Some of the
instruction will expect some or specific sets of these attributes.

gas::entry
Always written.

gas::exit
Written for all modes but okfail.

gas::exit::ok
Written for mode okfail.

gas::exit::fail
Written for mode okfail.

API

::grammar::me::cpu::gasm::begin g n ?mode? ?note?
This command starts the assembly of an instruction sequence, and (re)initializes
the state of the assembler. After completion of the instruction sequence use
::grammar::me::cpu::gasm::done to finalize the assembler.

It will operate on the graph g in the specified mode (Default is okfail). As part
of the initialization it will always create a standard .NOP instruction and label
it "entry". The creation of the remaining standard instructions is mode-dependent:

halt An "icf_halt" instruction labeled "exit/return".

!okfail
An "icf_ntreturn" instruction labeled "exit/return".

okfail Two .NOP instructions labeled "exit/ok" and "exit/fail" respectively.

The note, if specified (default is not), is given to the "entry" .NOP instruction.

The node reference n is simply stored for use by ::grammar::me::cpu::gasm::done. It
has to refer to a node in the tree t argument of that command.

After the initialization is done the "entry" instruction will be the anchor, and
the condition code will be set to always.

The command returns the empy string as its result.

::grammar::me::cpu::gasm::done --> t
This command finalizes the creation of an instruction sequence and then clears the
state of the assembler. NOTE that this does not delete any of the created
instructions. They can be made available to future begin/done cycles. Further
assembly will be possible only after reinitialization of the system via
::grammar::me::cpu::gasm::begin.

Before the state is cleared selected references to selected instructions will be
written to attributes of the node n in the tree t. Which instructions are saved is
mode-dependent. Both mode and the destination node n were specified during
invokation of ::grammar::me::cpu::gasm::begin.

Independent of the mode a reference to the instruction labeled "entry" will be
saved to the attribute gas::entry of n. The reference to the node n will further be
saved into the attribute "expr" of the "entry" instruction. Beyond that

halt A reference to the instruction labeled "exit/return" will be saved to the
attribute gas::exit of n.

okfail See halt.

!okfail
Reference to the two instructions labeled "exit/ok" and "exit/fail" will be
saved to the attributes gas::exit::ok and gas::exit::fail of n respectively.

The command returns the empy string as its result.

::grammar::me::cpu::gasm::state
This command returns the current state of the assembler. Its format is not
documented and considered to be internal to the package.

::grammar::me::cpu::gasm::state! s
This command takes a serialized assembler state s as returned by
::grammar::me::cpu::gasm::state and makes it the current state of the assembler.

Note that this may overwrite label definitions, however all non-conflicting label
definitions in the state before are not touched and merged with s.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::lift t dst = src
This command operates on the tree t. It copies the contents of the attributes
gas::entry, gas::exit::ok and gas::exit::fail from the node src to the node dst.
It returns the empty string as its result.

::grammar::me::cpu::gasm::Inline t node label
This command links an instruction sequence created by an earlier begin/done pair
into the current instruction sequence.

To this end it

[1] reads the instruction references from the attributes gas::entry,
gas::exit::ok, and gas::exit::fail from the node n of the tree t and makes
them available to assembler und the labels label/entry, label/exit::ok, and
label/exit::fail respectively.

[2] Creates an arc from the anchor to the node labeled label/entry, and tags it
with the current condition code.

[3] Makes the node labeled label/exit/ok the new anchor.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::Cmd cmd ?arg...?
This is the basic command to add instructions to the graph. It creates a new
instruction of type cmd with the given arguments arg... If the anchor was defined
it will also create an arc from the anchor to the new instruction using the current
condition code. After the call the new instruction will be the anchor and the
current condition code will be set to always.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::Bra
This is a convenience command to create a .BRA pseudo-instruction. It uses
::grammar::me::cpu::gasm::Cmd to actually create the instruction and inherits its
behaviour.

::grammar::me::cpu::gasm::Nop text
This is a convenience command to create a .NOP pseudo-instruction. It uses
::grammar::me::cpu::gasm::Cmd to actually create the instruction and inherits its
behaviour. The text will be saved as the first and only argument of the new
instruction.

::grammar::me::cpu::gasm::Note text
This is a convenience command to create a .C pseudo-instruction, i.e. a comment. It
uses ::grammar::me::cpu::gasm::Cmd to actually create the instruction and inherits
its behaviour. The text will be saved as the first and only argument of the new
instruction.

::grammar::me::cpu::gasm::Jmp label
This command creates an arc from the anchor to the instruction labeled with label,
and tags with the the current condition code.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::Exit
This command creates an arc from the anchor to one of the exit instructions, based
on the operation mode (see ::grammar::me::cpu::gasm::begin), and tags it with
current condition code.

For mode okfail it links to the instruction labeled either "exit/ok" or
"exit/fail", depending on the current condition code, and tagging it with the
current condition code For the other two modes it links to the instruction labeled
"exit/return", tagging it condition code always, independent the current condition
code.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::Who label
This command returns a reference to the instruction labeled with label.

::grammar::me::cpu::gasm::/Label name
This command labels the anchor with name. Note that an instruction can have more
than one label.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::/Clear
This command clears the anchor, leaving it undefined, and further resets the
current condition code to always.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::/Ok
This command sets the current condition code to ok.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::/Fail
This command sets the current condition code to fail.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::/At name
This command sets the anchor to the instruction labeled with name, and further
resets the current condition code to always.

The command returns the empty string as its result.

::grammar::me::cpu::gasm::/CloseLoop
This command marks the anchor as the last instruction in a loop body, by creating
the attribute LOOP.

The command returns the empty string as its result.

BUGS, IDEAS, FEEDBACK

       This  document,  and  the  package  it  describes, will undoubtedly contain bugs and other
       problems.   Please  report  such  in  the  category  grammar_me  of  the  Tcllib  Trackers
       [http://core.tcl.tk/tcllib/reportlist].  Please also report any ideas for enhancements you
       may have for either package and/or documentation.

KEYWORDS

       assembler, grammar, graph, parsing, tree, virtual machine

COPYRIGHT

       Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>

NAME

SYNOPSIS

DESCRIPTION

DEFINITIONS

API

BUGS, IDEAS, FEEDBACK

KEYWORDS

CATEGORY

COPYRIGHT