#   Copyright 2016 Robert Elder Software Inc.
#   
#   Licensed under the Apache License, Version 2.0 (the "License"); you may not 
#   use this file except in compliance with the License.  You may obtain a copy 
#   of the License at
#   
#       http://www.apache.org/licenses/LICENSE-2.0
#   
#   Unless required by applicable law or agreed to in writing, software 
#   distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 
#   WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the 
#   License for the specific language governing permissions and limitations 
#   under the License.

            One-Page CPU L2 Assembly Language Syntax Specification

The L2 assembly language is meant to augment the L1 language in such a way that
any conforming L1 file is also an L2 file, but not every L2 file is an L1 file.
The L2 language allows for statements that specify linkage information,
comments, and program offsets that are defined relatively.  I've recently made
a number of changes to this, and plan to make more in the future.  For now,
this grammar will suffice for describing the language:

interface_specifier
	:  "IMPLEMENTS"
	:  "REQUIRES"
	;

linkage_domain
	:  "INTERNAL"
	:  "EXTERNAL"
	;

symbol_linkage_declaration
	:  interface_specifier linkage_domain identifier
	:  interface_specifier "," interface_specifier linkage_domain identifier

offset_directive
	:  "OFFSET" "END"
	:  "OFFSET" "RELOCATABLE"
	:  "OFFSET" hexadecimal_number
	;

define_word_directive
	:  "DW" hexadecimal_number
	;

skip_words_directive
	:  "SW" hexadecimal_number
	;

string_directive
	:  "STRING" hexadecimal_number
	;

implemented_directive
	:  "IMPLEMENTED" hexadecimal_number
	;

required_directive
	:  "REQUIRED" hexadecimal_number
	;

unresolved_directive
	:  "UNRESOLVED" hexadecimal_number
	;

region_directive
	:  "REGION" hexadecimal_number
	;

start_directive
	:  "START" hexadecimal_number
	;

end_directive
	:  "END" hexadecimal_number
	;

permission_directive
	:  "PERMISSION" hexadecimal_number
	;

linkage_directive
	:  linkage_domain hexadecimal_number
	;

function_directive
	:  "FUNCTION" hexadecimal_number
	:  "FUNCTION" identifier identifier
	;

variable_directive
	:  "VARIABLE" hexadecimal_number
	:  "VARIABLE" identifier identifier
	;

constant_directive
	:  "CONSTANT" hexadecimal_number
	:  "CONSTANT" identifier identifier
	;

directive_statement
	:  offset_directive
	:  define_word_directive
	:  skip_words_directive
	:  function_directive
	:  variable_directive
	:  constant_directive
	:  string_directive
	:  implemented_directive
	:  required_directive
	:  unresolved_directive
	:  linkage_directive
	:  region_directive
	:  start_directive
	:  end_directive
	:  permission_directive
	:  symbol_linkage_declaration
	;

named_register
	:  "SP"
	:  "FP"
	:  "FR"
	:  "PC"
	:  "ZR"
	:  "WR"
	;

numbered_register
	: "r" decimal_number
	;

register
	: named_register
	: numbered_register
	;

branch_distance
	:  identifier
	:  decimal_number
	:  "-" decimal_number
	;

instruction_statement
	: "add" register register register
	: "sub" register register register
	: "mul" register register register
	: "div" register register register
	: "and" register register register
	: "or" register register register
	: "not" register register
	: "loa" register register
	: "sto" register register
	: "shr" register register
	: "shl" register register
	: "beq" register register branch_distance
	: "blt" register register branch_distance
	: "ll" register hexidecimal_number
	;

label_statement
	:  identifier ":"
	;

statement
	:  instruction_statement
	:  directive_statement
	:  label_statement
	;

after_statement
	:  newline statement_list
	:  comment newline statement_list
	:  comment 

statement_list
	:  after_statement
	:  statement after_statement
	:  epsilon
	;

l2_file
	: statement_list
	;

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