[//000000001]: # (grammar::me::cpu::gasm \- Grammar operations and usage) [//000000002]: # (Generated from file 'gasm\.man' by tcllib/doctools with format 'markdown') [//000000003]: # (Copyright © 2005 Andreas Kupries ) [//000000004]: # (grammar::me::cpu::gasm\(n\) 0\.1 tcllib "Grammar operations and usage")
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# NAME grammar::me::cpu::gasm \- ME assembler # Table Of Contents - [Table Of Contents](#toc) - [Synopsis](#synopsis) - [Description](#section1) - [DEFINITIONS](#section2) - [API](#section3) - [Bugs, Ideas, Feedback](#section4) - [Keywords](#keywords) - [Category](#category) - [Copyright](#copyright) # SYNOPSIS package require grammar::me::cpu::gasm ?0\.1? [__::grammar::me::cpu::gasm::begin__ *g* *n* ?*mode*? ?*note*?](#1) [__::grammar::me::cpu::gasm::done__ __\-\->__ *t*](#2) [__::grammar::me::cpu::gasm::state__](#3) [__::grammar::me::cpu::gasm::state\!__ *s*](#4) [__::grammar::me::cpu::gasm::lift__ *t* *dst* __=__ *src*](#5) [__::grammar::me::cpu::gasm::Inline__ *t* *node* *label*](#6) [__::grammar::me::cpu::gasm::Cmd__ *cmd* ?*arg*\.\.\.?](#7) [__::grammar::me::cpu::gasm::Bra__](#8) [__::grammar::me::cpu::gasm::Nop__ *text*](#9) [__::grammar::me::cpu::gasm::Note__ *text*](#10) [__::grammar::me::cpu::gasm::Jmp__ *label*](#11) [__::grammar::me::cpu::gasm::Exit__](#12) [__::grammar::me::cpu::gasm::Who__ *label*](#13) [__::grammar::me::cpu::gasm::/Label__ *name*](#14) [__::grammar::me::cpu::gasm::/Clear__](#15) [__::grammar::me::cpu::gasm::/Ok__](#16) [__::grammar::me::cpu::gasm::/Fail__](#17) [__::grammar::me::cpu::gasm::/At__ *name*](#18) [__::grammar::me::cpu::gasm::/CloseLoop__](#19) # 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 \(See package __[struct::graph](\.\./struct/graph\.md)__\) 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*\. 1. 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\. 1. The condition code to use when creating arcs between instructions, which is one of __always__, __ok__, and __fail__\. 1. The current operation mode, one of __halt__, __okfail__, and __\!okfail__\. 1. 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](\.\./struct/graph\.md)__\. 1. Any tree object command used by the assembler has to provide the API as specified in the documentation for the package __[struct::tree](\.\./struct/struct\_tree\.md)__\. 1. 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\. 1. 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\. 1. 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\. 1. Creates an arc from the *anchor* to the node labeled *label*/entry, and tags it with the current condition code\. 1. 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\. When proposing code changes, please provide *unified diffs*, i\.e the output of __diff \-u__\. Note further that *attachments* are strongly preferred over inlined patches\. Attachments can be made by going to the __Edit__ form of the ticket immediately after its creation, and then using the left\-most button in the secondary navigation bar\. # KEYWORDS [assembler](\.\./\.\./\.\./\.\./index\.md\#assembler), [grammar](\.\./\.\./\.\./\.\./index\.md\#grammar), [graph](\.\./\.\./\.\./\.\./index\.md\#graph), [parsing](\.\./\.\./\.\./\.\./index\.md\#parsing), [tree](\.\./\.\./\.\./\.\./index\.md\#tree), [virtual machine](\.\./\.\./\.\./\.\./index\.md\#virtual\_machine) # CATEGORY Grammars and finite automata # COPYRIGHT Copyright © 2005 Andreas Kupries