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wwwbasic.js
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// Copyright 2018 Google LLC
//
// 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
//
// https://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.
'use strict';
(function() {
var DYNAMIC_HEAP_SIZE = 1024 * 1024 * 16;
var MAX_DIMENSIONS = 7;
var BLACK = 0xff000000;
var WHITE = 0xffffffff;
var SIMPLE_TYPE_INFO = {
'byte': {array: 'Uint8Array', size: 1, shift: 0, view: 'b'},
'short': {array: 'Int16Array', size: 2, shift: 1, view: 'i16'},
'long': {array: 'Int32Array', size: 4, shift: 2, view: 'i'},
'single': {array: 'Float32Array', size: 4, shift: 2, view: 's'},
'double': {array: 'Float64Array', size: 8, shift: 3, view: 'd'},
'string': {array: 'Array', size: 1, shift: 0, view: 'str'},
};
var IMPLICIT_TYPE_MAP = {
'$': 'string', '%': 'short', '&': 'long', '!': 'single', '#': 'double',
};
function NextChar(ch) {
return String.fromCharCode(ch.charCodeAt(0) + 1);
}
function RenderFont(ctx, height) {
var data = new Uint8Array(256 * 8 * height);
var pos = 0;
for (var i = 0; i < 256; ++i) {
ctx.fillStyle = '#000';
ctx.fillRect(0, 0, 16, 32);
ctx.textBaseline = 'top';
ctx.font = 'bold 16px monospace';
ctx.save();
ctx.scale(1, height / 16);
ctx.fillStyle = '#fff';
ctx.fillText(CHARSET.charAt(i), 0, 0);
ctx.restore();
var pix = ctx.getImageData(0, 0, 8, height);
var pdata = pix.data;
for (var j = 0; j < pdata.length; j += 4) {
var level = pdata[j] * 0.1140 +
pdata[j + 1] * 0.5870 +
pdata[j + 2] * 0.2989;
data[pos++] = level > 128 ? 255 : 0;
}
}
return data;
}
function LoadFont(s, dup) {
var data = new Uint8Array(s.length * dup);
var pos = 0;
for (var i = 0; i < 256; ++i) {
var row = Math.floor(i / 8);
var col = i % 8;
for (var y = 0; y < 8; ++y) {
for (var d = 0; d < dup; ++d) {
for (var x = 0; x < 8; ++x) {
data[pos++] = s[x + y * 8 * 8 + col * 8 + row * 64 * 8]
!= ' ' ? 255 : 0;
}
}
}
}
return data;
}
function CreateFont(ctx, height) {
if (height == 8) {
return LoadFont(FONT8, 1);
} else if (height == 16) {
return LoadFont(FONT8, 2);
} else {
return RenderFont(ctx, height);
}
}
function Interpret(code, canvas, from_tag) {
// Display Info (in browser only).
var screen_mode = 0;
var screen_bpp = 4;
var text_width = 80;
var text_height = 60;
var font_height = 16;
var screen_aspect = 1;
var font_data;
var ctx;
var display;
var display_data;
var scale_canvas;
var audio_ctx = new window.AudioContext; /* Context for the audio playback, beep, sound commands */
var audio_sampleRate = audio_ctx.sampleRate; /* Get sample rate from the audio context, needed for proper timing */
var PlayNote_Tempo = 120; /* Default to 120 quarter notes per second. */
var PlayNote_Duration = 4; /* set default to quarter note */
var PlayNote_Octave = 3; /* Can't find much on the default. But figured 0 - 6 and picked the mid */
var PlayNote_LegatoStaccato = 7/8;
var PlayNote_Volume = 200;
var bPlayNote_Foreground = true; /* play in the foreground, block application until music is done */
var bPlayNote_PWM_Mode = true; /* use sine waves or PWM like the cassic systems */
function SetupDisplay(width, height, aspect, fheight) {
if (!canvas) {
return;
}
ctx = canvas.getContext('2d', { alpha: false });
display = ctx.createImageData(width, height);
display_data = new Uint32Array(display.data.buffer);
if (!scale_canvas) {
scale_canvas = document.createElement('canvas');
}
scale_canvas.width = width;
scale_canvas.height = height;
text_width = Math.floor(width / 8);
text_height = Math.floor(height / fheight);
screen_aspect = aspect;
font_height = fheight;
var sctx = scale_canvas.getContext('2d', { alpha: false});
font_data = CreateFont(sctx, font_height);
}
Screen(0);
var debugging_mode = typeof debug == 'boolean' && debug;
// Parsing and Run State.
var labels = {};
var data_labels = {};
var flow = [];
var types = {};
var subroutines = {};
var functions = {};
var global_vars = {};
var vars = global_vars;
var allocated = 0;
var str_count = 0;
var const_count = 0;
var var_decls = '';
var rstack = [];
var data = [];
var data_pos = 0;
var ops = [];
var curop = '';
var ip = 0;
// Input State
var keys = [];
var mouse_x = 0;
var mouse_y = 0;
var mouse_buttons = 0;
var mouse_wheel = 0;
var mouse_clip = 0;
// Language Options
var option_base = 0;
var option_explicit = false;
// Variable declaration defaults.
var letter_default = {};
// Default is single.
var i = 'a';
do {
letter_default[i] = 'single';
i = NextChar(i);
} while (i != 'z');
// Yield State
var yielding = 0;
var quitting = 0;
var delay = 0;
// Drawing and Console State
var color_map;
var reverse_color_map;
var fg_color = WHITE;
var bg_color = BLACK;
var text_x = 0;
var text_y = 0;
var pen_x = 0;
var pen_y = 0;
var toklist = [
':', ';', ',', '(', ')', '{', '}', '[', ']',
'+=', '-=', '*=', '/=', '\\=', '^=', '&=',
'+', '-', '*', '/', '\\', '^', '&', '.',
'<=', '>=', '<>', '=>', '=', '<', '>', '@', '\n',
];
code = code.replace(/\r/g, ' ');
code = code.replace(/\t/g, ' ');
if (from_tag) {
code = code.replace(/</g, '<');
code = code.replace(/>/g, '>');
code = code.replace(/&/g, '&');
}
var tok = null;
var line = canvas ? 0 : 1;
function Next() {
tok = '';
for (;;) {
while (code.substr(0, 1) == ' ' ||
code.substr(0, 1) == '\t') {
if (tok != '') {
return;
}
code = code.substr(1);
}
if (code.search(/^_[ \t]*('[^\n]*)?\n/) != -1) {
if (tok != '') {
return;
}
code = code.substr(code.search('\n') + 1);
++line;
continue;
}
if (code.substr(0, 1) == '\'') {
if (tok != '') {
return;
}
while (code.length > 0 && code.substr(0, 1) != '\n') {
code = code.substr(1);
}
continue;
}
if (code.substr(0, 1) == '"') {
if (tok != '') {
return;
}
tok = '"';
code = code.substr(1);
while (code.length > 0 && code.substr(0, 1) != '"') {
if (code.substr(0, 1) == '\n') {
// Allow strings to cut off at end of line.
// GW-Basic seems to allow it.
tok += '"';
return;
}
tok += code.substr(0, 1);
code = code.substr(1);
}
tok += '"';
code = code.substr(1);
return;
}
if (tok == '' && /[.0-9][#]?/.test(code.substr(0, 1))) {
var n = code.match(/^([0-9]*([.][0-9]*)?([eE][+-]?[0-9]+)?[#]?)/);
if (n === null) {
Throw('Bad number');
}
tok = n[1];
code = code.substr(tok.length);
return;
}
for (var i = 0; i < toklist.length; ++i) {
if (code.substr(0, toklist[i].length) == toklist[i]) {
if (tok != '') {
if (code.substr(0, 1) == '&' &&
code.substr(code.length - 1) != '$') {
tok += '&';
code = code.substr(1);
}
return;
}
tok = toklist[i];
code = code.substr(toklist[i].length);
if (tok == '\n') {
++line;
tok = '<EOL>';
} else if (tok == '&' && code.substr(0, 1).toLowerCase() == 'h') {
code = code.substr(1);
var n = code.match(/^([0-9a-fA-F]+)/);
if (n === null) {
Throw('Bad hex number');
}
tok = '0x' + n[1];
code = code.substr(n[1].length);
}
return;
}
}
tok += code.substr(0, 1).toLowerCase();
code = code.substr(1);
if (code == '') {
return;
}
}
}
Next();
function ConsumeData() {
var quote = false;
var had_quote = false;
var item = '';
for (;;) {
var ch = code.substr(0, 1);
if (ch == '\n' || ch == '') {
if (!had_quote) {
if (!quote) {
item = item.trim();
}
data.push(item);
}
break;
} else if (ch == '"') {
if (quote) {
data.push(item);
item = '';
quote = false;
had_quote = true;
} else {
quote = true;
if (item.search(/[^ \t]/) != -1) {
Throw('Data statement extra text: "' + item + '"');
}
item = '';
}
} else if (ch == ',') {
if (!quote) {
if (!had_quote) {
data.push(item.trim());
} else {
had_quote = false;
if (item.search(/[^ \t]/) != -1) {
Throw('Data statement extra text: "' + item + '"');
}
}
item = '';
} else {
item += ',';
}
} else {
item += ch;
}
code = code.substr(1);
}
Next();
}
function Throw(msg) {
throw msg + ' at line ' + line;
}
function Skip(t) {
if (tok != t) {
Throw('Expected "' + t + '" found "' + tok + '"');
}
Next();
}
function EndOfStatement() {
return tok == ':' || tok == '<EOL>';
}
function SkipEndOfStatement() {
if (!EndOfStatement()) {
Throw('Expected : or EOL');
}
Next();
}
function NewOp() {
ops.push(curop);
curop = '';
}
function If(e, n) {
if (n === undefined) {
n = [];
}
NewOp();
ops[ops.length - 1] += 'if (!(' + e + ')) { ip = ';
flow.push(['if', ops.length - 1, []]);
}
function Else() {
var f = flow.pop();
if (f[0] != 'if') {
Throw('ELSE unmatched to IF');
}
NewOp();
var pos = ops.length - 1;
ops[pos] += 'ip = ';
NewOp();
ops[f[1]] += ops.length + '; }\n';
flow.push(['else', null, f[2].concat(pos)]);
}
function ElseIf(e) {
var f = flow.pop();
if (f[0] != 'if') {
Throw('ELSEIF unmatched to IF');
}
NewOp();
var pos = ops.length - 1;
ops[pos] += 'ip = ';
NewOp();
ops[f[1]] += ops.length + '; }\n';
NewOp();
ops[ops.length - 1] += 'if (!(' + e + ')) { ip = ';
flow.push(['if', ops.length - 1, f[2].concat([pos])]);
}
function EndIf() {
NewOp();
var f = flow.pop();
if (f[0] == 'else') {
// nothing needed
} else if (f[0] == 'if') {
ops[f[1]] += ops.length + '; }\n';
} else {
Throw('Unmatch end if');
}
for (var i = 0; i < f[2].length; ++i) {
ops[f[2][i]] += ops.length + ';\n';
}
}
function AddLabel(name) {
if (labels[name] !== undefined) {
Throw('Label ' + name + ' defined twice');
}
NewOp();
curop += '// LABEL ' + name + ':\n';
labels[name] = ops.length;
data_labels[name] = data.length;
}
function Factor3() {
if (tok == '(') {
Skip('(');
var ret = Expression();
Skip(')');
return ret;
} else {
var name = tok;
Next();
if (name.substr(0, 1) == '"' ||
/^[0-9]*([.][0-9]*)?([eE][+-]?[0-9]+)?$/.test(name) ||
/^0x[0-9a-fA-F]+$/.test(name)) {
return name;
}
if (name == 'rnd') {
if (tok == '(') {
Skip('(');
if (tok != ')') {
var e = Expression();
}
Skip(')');
}
return 'Math.random()';
}
if (name == 'varptr') {
Skip('(');
var vname = tok;
Next();
Skip(')');
if (vars[vname] === undefined) {
Throw('Undefined variable name');
}
return vars[vname].offset;
}
if (name == 'log' || name == 'ucase$' || name == 'lcase$' ||
name == 'chr$' || name == 'sqr' ||
name == 'int' || name == 'cint' ||
name == 'abs' || name == 'len' || name == 'val' ||
name == 'cos' || name == 'sin' || name == 'tan' || name == 'atn' ||
name == 'exp' || name == 'str$' || name == 'peek' ||
name == 'ltrim$' || name == 'rtrim$' ||
name == 'space$' || name == 'tab') {
Skip('(');
var e = Expression();
Skip(')');
switch (name) {
case 'log': return 'Math.log(' + e + ')';
case 'ucase$': return '(' + e + ').toUpperCase()';
case 'lcase$': return '(' + e + ').toLowerCase()';
case 'chr$': return 'String.fromCharCode(' + e + ')';
case 'asc': return '(' + e + ').toCharCode(0)';
case 'sqr': return 'Math.sqrt(' + e + ')';
case 'int': return 'Math.floor(' + e + ')';
case 'cint': return 'Math.floor(' + e + ')';
case 'abs': return 'Math.abs(' + e + ')';
case 'cos': return 'Math.cos(' + e + ')';
case 'sin': return 'Math.sin(' + e + ')';
case 'tan': return 'Math.tan(' + e + ')';
case 'atn': return 'Math.atan(' + e + ')';
case 'exp': return 'Math.exp(' + e + ')';
case 'str$': return '(' + e + ').toString()';
case 'val': return 'parseInt(' + e + ')';
case 'peek': return 'Peek(' + e + ').toString()';
case 'len': return '((' + e + ').length)';
case 'ltrim$': return '((' + e + ').trimStart())';
case 'rtrim$': return '((' + e + ').trimEnd())';
case 'space$': return 'StringRep((' + e + '), " ")';
case 'tab': return 'StringRep((' + e + '), "\t")';
}
Throw('This cannot happen');
}
if (name == 'atan2' || name == 'string$' ||
name == 'left$' || name == 'right$' ||
name == 'instr' || name == 'point') {
Skip('(');
var a = Expression();
Skip(',');
var b = Expression();
Skip(')');
if (name == 'atan2') {
return 'Math.atan2(' + a + ', ' + b + ')';
} else if (name == 'string$') {
return 'StringRep(' + a + ', ' + b + ')';
} else if (name == 'left$') {
return '((' + a + ').substr(0, (' + b + ')))';
} else if (name == 'right$') {
return 'Right((' + a + '), (' + b + '))';
} else if (name == 'instr') {
return '(' + a + ').search(' + b + ')';
} else if (name == 'point') {
return 'Point((' + a + '), (' + b + '))';
} else {
throw 'impossible';
}
}
if (name == 'mid$') {
Skip('(');
var a = Expression();
Skip(',');
var b = Expression();
Skip(',');
var c = Expression();
Skip(')');
return '((' + a + ').substr((' + b + '), (' + c + ')))';
}
if (name == 'inkey$') {
return 'Inkey()';
}
if (name == 'timer') {
return 'GetTimer()';
}
if (functions[name] !== undefined) {
Skip('(');
while (tok != ')') {
var a = Expression();
if (tok != ',') {
break;
}
Skip(',');
}
Skip(')');
// TODO: Implement.
return '0';
}
return IndexVariable(name);
}
}
function Factor2() {
var a = Factor3();
while (tok == '^') {
Next();
var b = Factor3();
a = 'Math.pow(' + a + ', ' + b + ')';
}
return a;
}
function Factor1() {
var ret = '';
while (tok == '+' || tok == '-') {
ret += tok;
Next();
}
return ret + '(' + Factor2() + ')';
}
function Factor() {
var a = Factor1();
while (tok == '*' || tok == '/') {
var op = tok;
Next();
var b = Factor1();
a = '(' + a + ')' + op + '(' + b + ')';
}
return a;
}
function Term2() {
var a = Factor();
while (tok == '\\') {
var b = Next();
Factor();
a = 'Math.floor((' + a + ')/(' + b + '))';
}
return a;
}
function Term1() {
var a = Term2();
while (tok == 'mod') {
Next();
var b = Term2();
a = '((' + a + ')%(' + b + '))';
}
return a;
}
function Term() {
var a = Term1();
while (tok == '+' || tok == '-') {
var op = tok;
Next();
var b = Term1();
a = '(' + a + ')' + op + '(' + b + ')';
}
return a;
}
function Relational() {
var a = Term();
while (tok == '=' || tok == '<' || tok == '>' ||
tok == '<>' || tok == '<=' || tok == '>=' || tok == '=>') {
var op = tok;
Next();
if (op == '=>') {
op = '>=';
}
var b = Term();
if (op == '=') {
a = '(' + a + ') == (' + b + ') ? -1 : 0';
} else if (op == '<>') {
a = '(' + a + ') != (' + b + ') ? -1 : 0';
} else {
a = '(' + a + ') ' + op + ' (' + b + ') ? -1 : 0';
}
}
return a;
}
function Logical1() {
var ret = '';
while (tok == 'not') {
Next();
ret += '~';
}
return ret + '(' + Relational() + ')';
}
function Logical() {
var a = Logical1();
while (tok == 'and') {
Next();
var b = Logical1();
a = '(' + a + ') & (' + b + ')';
}
return a;
}
function Expression() {
var a = Logical();
while (tok == 'or') {
Next();
var b = Logical();
a = '(' + a + ') | (' + b + ')';
}
return a;
}
function TypeName() {
if (SIMPLE_TYPE_INFO[tok]) {
var type = tok;
Next();
return type;
} else if (tok == 'integer') {
Skip('integer');
return 'long';
} else if (tok == 'any') {
Skip('any');
// TODO: Handle this properly.
return 'string';
} else if (types[tok] !== undefined) {
var type_name = tok;
if (types[type_name] === undefined) {
Throw('Undefined type');
}
Next();
return type_name;
}
Throw('Undefined type "' + tok + '"');
}
function ImplicitType(name) {
return IMPLICIT_TYPE_MAP[name[name.length - 1]] ||
letter_default[name[0]] || 'single';
}
function Align(alignment) {
allocated = Math.floor((allocated + alignment - 1) /
alignment) * alignment;
}
function Allocate(size) {
Align(size > 8 ? 8 : size);
var ret = allocated;
allocated += size;
return ret;
}
function DimScalarVariable(name, type_name, defaults) {
var info = types[type_name] || SIMPLE_TYPE_INFO[type_name];
if (info === undefined) {
Throw('Unknown type');
}
var size = info.size;
var offset;
if (type_name == 'string') {
offset = str_count++;
} else {
offset = Allocate(size);
}
var_decls += '// ' + name + ' is at ' + offset + '\n';
vars[name] = {
offset: offset,
dimensions: 0,
type_name: type_name,
};
if (defaults.length > 0) {
curop += IndexVariable(name) + ' = ' + defaults[0] + ';\n';
}
}
function MaybeImplicitDimVariable(name) {
// TODO: Handle array variables.
if (global_vars[name] !== undefined) {
return global_vars[name];
}
if (vars[name] !== undefined) {
return vars[name];
}
if (option_explicit) {
Throw('Undeclared variable ' + name);
}
var type_name = ImplicitType(name);
DimScalarVariable(name, type_name, []);
return vars[name];
}
function ArrayPart(offset, i) {
return SIMPLE_TYPE_INFO['long'].view + '[' + ((offset >> 2) + i) + ']';
}
function ReserveArrayCell(name) {
if (vars[name] === undefined) {
var offset = Allocate(4 + MAX_DIMENSIONS * 4 * 2);
vars[name] = {
offset: offset,
dimensions: null,
type_name: null,
};
var_decls += '// ' + name + ' is at ' + ArrayPart(offset, 0) +
' (cell-addr: ' + offset + ')\n';
}
return vars[name];
}
function DimVariable(default_tname, redim) {
var name = tok;
Next();
// Pick default.
if (default_tname === null) {
default_tname = ImplicitType(name);
}
var type_name = default_tname;
var dimensions = [];
var defaults = [];
var is_scalar = true;
if (tok == '(') {
Skip('(');
is_scalar = false;
while (tok != ')') {
var e = Expression();
var d = 'dim' + const_count++;
var_decls += 'const ' + d + ' = (' + e + ');\n';
if (tok == 'to') {
Skip('to');
var e1 = Expression();
var d1 = 'dim' + const_count++;
var_decls += 'const ' + d1 + ' = (' + e1 + ');\n';
dimensions.push([d, d1]);
} else {
dimensions.push([option_base, d]);
}
if (tok != ',') {
break;
}
Skip(',');
}
Skip(')');
if (tok == '=') {
Skip('=');
Skip('{');
var e = Expression();
defaults.push(e);
while (tok == ',') {
Skip(',');
var e = Expression();
defaults.push(e);
}
Skip('}');
}
} else if (tok == '=') {
Skip('=');
var e = Expression();
defaults.push(e);
}
if (tok == 'as') {
Skip('as');
type_name = TypeName();
}
if (vars[name] !== undefined && vars[name].dimensions != null) {
if (redim) {
return;
}
Throw('Variable ' + name + ' defined twice');
}
// name, dims.
if (is_scalar) {
DimScalarVariable(name, type_name, defaults);
} else {
if (dimensions.length > MAX_DIMENSIONS) {
Throw('Too many dimensions');
}
var offset = ReserveArrayCell(name).offset;
var info = types[type_name] || SIMPLE_TYPE_INFO[type_name];
var parts = [];
for (var i = 0; i < dimensions.length; i++) {
parts.push('((' + dimensions[i][1] + ')-(' +
dimensions[i][0] + ')+1)');
}
curop += 'if (' + ArrayPart(offset, 0) + ' === 0) {\n';
curop += ' ' + ArrayPart(offset, 0) + ' = Allocate(' +
[info.size].concat(parts).join('*') + ');\n';
for (var i = 0; i < dimensions.length; i++) {
curop += ' ' + ArrayPart(offset, i * 2 + 1) + ' = ' +
dimensions[i][0] + ';\n';
curop += ' ' + ArrayPart(offset, i * 2 + 2) + ' = ' +
[info.size].concat(parts).slice(0, i + 1).join('*') + ';\n';
}
if (defaults.length > 0) {
if (dimensions.length > 1) {
Throw('Only 1-d array defaults supported');
}
if (!SIMPLE_TYPE_INFO[type_name]) {
Throw('Only simple type array defaults supported');
}
for (var i = 0; i < defaults.length; i++) {
curop += ' ' + info.view + '[' +
' + (' + ArrayPart(offset, 0) + ' >> ' + info.shift + ') + '
+ i + '] = (' + defaults[i] + ');\n';
}
}
curop += '}\n';
vars[name] = {
offset: offset,
dimensions: dimensions.length > 0 ? dimensions.length : -1,
type_name: type_name,
};
}
}
function IndexVariable(name) {
var v = MaybeImplicitDimVariable(name);
var offset = v.offset;
var type_name = v.type_name;
while (tok == '(' || tok == '.') {
if (tok == '(') {
Skip('(');
var dims = [];
while (tok != ')') {
var e = Expression();
dims.push(e);
if (tok != ',') {
break;
}
Skip(',');
}
Skip(')');
var info = types[type_name] || SIMPLE_TYPE_INFO[type_name];
var noffset = '(' + ArrayPart(offset, 0) + ' + (';
if (v.dimensions !== -1 && dims.length != v.dimensions) {
Throw('Array dimension expected ' + v.dimensions +
' but found ' + dims.length + ', array named: ' + name);
}
for (var i = 0; i < dims.length; ++i) {
noffset += '(((' + dims[i] + ')|0)-' +
ArrayPart(offset, i * 2 + 1) + ')';
noffset += '*' + ArrayPart(offset, i * 2 + 2);
if (i != dims.length - 1) {
noffset += '+';
}
}
noffset += '))';
offset = noffset;
} else if (tok == '.') {
Skip('.');
v = types[type_name];
if (v === undefined) {
Throw('Not a struct type');
}
var field = v.vars[tok];
if (field === undefined) {
Throw('Invalid field name');
}
Next();
offset = '(' + offset + ' + ' + field.offset + ')';
type_name = field.type_name;
}
}
var info = SIMPLE_TYPE_INFO[type_name];
if (!info) {
Throw('Expected simple type');
}
return info.view + '[' + offset + '>>' + info.shift + ']';
}
function End() {
yielding = 1;
quitting = 1;
if (canvas) {
console.log('BASIC END');
} else {
if (output_buffer != '') {
PutCh(null);
}
}
}
function Sleep(t) {
yielding = 1;
delay = t;
}
function Inkey() {
yielding = 1;
if (keys.length > 0) {
return keys.shift();
} else {
return '';
}
}
function Yield() {
yielding = 1;
}
function Right(s, n) {
return s.substr(s.length - n);
}
function Point(x, y) {
// TODO: Implement.
return 0;
}
function StringRep(n, ch) {
var ret = '';
var cch;
if (typeof ch == 'string') {
cch = ch;
} else {
cch = String.fromCharCode(ch);
}
for (var i = 0; i < n; ++i) {
ret += cch;
}
return ret;
}
function Peek(addr) {
return 0;
}
function RGB(r, g, b) {
return BLACK | r | (g << 8) | (b << 16);
}
function Screen(mode) {