#   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 L1 Assembly Language Syntax Specification

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:

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
	;

function_directive
	:  "FUNCTION" hexadecimal_number
	;

variable_directive
	:  "VARIABLE" hexadecimal_number
	;

constant_directive
	:  "CONSTANT" hexadecimal_number
	;

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

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

numbered_register
	: "r" decimal_number
	;

register
	: named_register
	: numbered_register
	;

branch_distance
	:  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
	;

statement
	:  instruction_statement
	:  directive_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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