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<!DOCTYPE html>
<title>Logo Language Guide</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
<script src="https://cdn.rawgit.com/inexorabletash/polyfill/v0.1.29/polyfill.min.js"></script>
<style>
h1, h2, h3, h4, p { margin-bottom: 6pt; margin-top: 6pt; }
body, p, h1, h2, h3 { font-family: sans-serif; }
dl { margin-top: 6pt; }
p, dt, dd, ol, li { font-size: 10pt; }
code { font-family: monospace; font-weight: bold; }
body
{
color: black;
background-color: transparent;
}
dd.example:before {
content: 'Example:';
margin-right: 0.5em;
font-family: sans-serif;
font-style: italic;
color: gray;
}
dd.example {
font-family: monospace;
white-space: pre-wrap;
margin-top: 2px;
margin-bottom: 2px;
color: gray;
cursor: pointer;
}
</style>
<div>
<p>The section numbers are per the <a target="_blank" href="https://www.cs.berkeley.edu/~bh/v2ch14/manual.html">Berkeley Logo Reference Manual</a> in Brian Harvey's <cite>Computer Science Logo Style volume 2: Advanced Techniques</cite> for ease
of comparison.</p>
<ol>
<li><a href="#types">Data Types and Syntax</a>
<li><a href="#sec2">Data Structure Primitives</a>
<li><a href="#sec3">Communication</a>
<li><a href="#sec4">Arithmetic</a>
<li><a href="#sec5">Logical Operations</a>
<li><a href="#sec6">Graphics</a>
<li><a href="#sec7">Workspace Management</a>
<li><a href="#sec8">Control Structures</a>
</ol>
<h3 id="types">Data Types and Syntax</h3>
<dl>
<dt><code>"<var>word</var></code>
<dt><code>'<var>word</var></code>
<dt><code><var>number</var></code>
<dd>Word. (Quoted words are terminated by [](){} or whitespace, \ to escape.)
<dd class=example>show "hello</dd>
<dd class=example>show "hello\ logo</dd>
<dd class=example>show 12.34</dd>
<dt><code>:<var>variable</var></code>
<dd>Input definition/variable reference
<dd class=example>show :name</dd>
<dt><code>[ <var>word ...</var> ]</code>
<dd>List of words or lists, whitespace separated
<dd class=example>show [1 2 3]</dd>
<dt><code>{ <var>word ...</var> }</code>
<dt><code>{ <var>word ...</var> }@<var>origin</var></code>
<dd>Array of words, whitespace separated
<dd class=example>show {1 2 3}</dd>
<dt><code> ( <var>expression</var> )</code>
<dd>Parenthesis can be used to group expressions
<dd class=example>show ( 1 + 2 ) * 3</dd>
<dt><code><var>procedure</var> <var>input</var> ...</code>
<dd>Call procedure with default number of inputs
<dd class=example>show "hello</dd>
<dt><code> ( <var>procedure</var> <var>input</var> ... )</code>
<dd>Call procedure with an arbitrary number of inputs
<dd class=example>(show "hello :name)</dd>
</dl>
<h3 id="sec2">2. Data Structure Primitives</h3>
<h4>2.1 Constructors</h4>
<dl>
<dt><code>word <var>expr</var> <var>expr</var></code>
<dt><code>(word <var>expr</var> <var>...</var>)</code>
<dd>Concatenate two (or more) words into one word
<dd class=example>show (word "a "b "c)</dd>
<dt><code>list <var>thing1</var> <var>thing2</var></code>
<dt><code>(list <var>thing1</var> <var>thing2</var> ...)</code>
<dd>Create a new list from the inputs
<dd class=example>show (list 1+2 2+3 3+4)</dd>
<dt><code>sentence thing1 thing2</code>
<dt><code>(sentence thing1 thing2 ...)</code>
<dt><code>se thing1 thing2</code>
<dt><code>(se thing1 thing2 ...)</code>
<dd>Create a new list from the inputs (if non-lists) or members of the inputs (if lists)
<dd class=example>show sentence [1 2 3] [and so on]</dd>
<dt><code>fput <var>thing</var> <var>list</var></code>
<dt><code>lput <var>thing</var> <var>list</var></code>
<dd>Outputs list, but with thing added as a new first/last item; if list is a word, concatenates
<dd class=example>show fput 0 [ 1 2 3 ]</dd>
<dd class=example>show fput "a "bcd</dd>
<dd class=example>show lput 4 [ 1 2 3 ]</dd>
<dd class=example>show lput "e "bcd</dd>
<dt><code>array <var>size</var></code>
<dt><code>(array <var>size</var> <var>origin</var>)</code>
<dd>Create a new array. The default origin is 1.
<dd class=example>show array 10</dd>
<dt><code>mdarray [<var>dimensions</var> ...]</code>
<dt><code>(mdarray [<var>dimensions</var> ...] <var>origin</var>)</code>
<dd>Create a new multi-dimensional array. The default origin is 1.
<dd class=example>show mdarray [2 2]</dd>
<dt><code>listtoarray <var>list</var></code>
<dt><code>(listtoarray <var>list</var> <var>origin</var>)</code>
<dd>Create a new array populated by members of a list
<dd class=example>show listtoarray [ 1 3 5 7 ]</dd>
<dt><code>arraytolist <var>array</var></code>
<dd>Create a new list populated by members of a array
<dd class=example>show arraytolist { 2 4 6 8 }</dd>
<dt><code>combine thing1 thing2</code>
<dd>If thing2 is a word, like <code>word</code>; otherwise, like <code>fput</code>
<dd class=example>show combine "a [b c]</dd>
<dt><code>reverse <var>list</var></code>
<dd>Outputs a list with the items in reverse order; if input is a word, reverses characters
<dd class=example>show reverse [ 1 2 3 ]</dd>
<dd class=example>show reverse "abc</dd>
<dt><code>gensym</code>
<dd>Outputs a unique string, e.g. <samp>G1</samp>, <samp>G2</samp>, etc.
<dd class=example>show gensym</dd>
</dl>
<h4>2.2 Data Selectors</h4>
<dl>
<dt><code>first <var>list</var></code>
<dt><code>last <var>list</var></code>
<dd>Outputs the first or last item (or character) from the list (or word), respectively
<dd class=example>show first [ 1 2 3 ]</dd>
<dd class=example>show first "abc</dd>
<dd class=example>show last [ 1 2 3 ]</dd>
<dd class=example>show last "abc</dd>
<dt><code>firsts <var>listoflists</var></code>
<dd>Outputs a list of the first item (or character) of each sublist (or word)
<dd class=example>show firsts [ [1 2 3] [a b c] ]</dd>
<dd class=example>show firsts [ abc def ]</dd>
<dt><code>butfirst <var>list</var></code>
<dt><code>bf <var>list</var></code>
<dt><code>butlast <var>list</var></code>
<dt><code>bl <var>list</var></code>
<dd>Outputs the list (or word), except for the first/last item (or character)
<dd class=example>show butfirst [ 1 2 3 ]</dd>
<dd class=example>show butfirst "abc</dd>
<dd class=example>show butlast [ 1 2 3 ]</dd>
<dd class=example>show butlast "abc</dd>
<dt><code>butfirsts <var>listoflists</var></code>
<dt><code>bfs <var>listoflists</var></code>
<dd>Outputs a list of sublists (or words) without the first item (or characters)
<dd class=example>show butfirsts [ [ 1 2 3 ] [ a b c ] ]</dd>
<dd class=example>show butfirsts [ abc def ]</dd>
<dt><code>item <var>index</var> <var>thing</var></code>
<dd>Outputs the indexth item of the list or array or word
<dd class=example>show item 2 [ 1 2 3 ]</dd>
<dd class=example>show item 2 "abc</dd>
<dt><code>mditem [<var>index</var> ...] <var>thing</var></code>
<dd>Outputs an item from a multi-dimensional array
<dd class=example>show mditem [2 1] {{a b} {c d}}</dd>
<dt><code>pick <var>list</var></code>
<dd>Outputs one item from a list (or word), at random
<dd class=example>show pick [ 1 2 3 ]</dd>
<dd class=example>show pick "abc</dd>
<dt><code>remove <var>thing</var> <var>list</var></code>
<dd>Outputs the list (or word) with any occurences of thing removed
<dd class=example>show remove "b [ a b c ]</dd>
<dd class=example>show remove "a "banana</dd>
<dt><code>remdup <var>list</var></code>
<dd>Outputs the list (or word) with duplicates removed
<dd class=example>show remdup [ 1 2 3 2 3 4 3 4 5 ]</dd>
<dd class=example>show remdup "banana</dd>
<dt><code>quoted <var>thing</var></code>
<dd>Outputs thing with " prepended if a word, or just thing otherwise.
<dd class=example>show quoted "abc</dd>
<dt><code>split <var>thing</var> <var>list</var></code>
<dd>Outputs the list split into a list of lists (or list of words) wherever thing appears.
<dd class=example>show split "a "banana</dd>
<dd class=example>show split 3 [1 2 3 4 1 2 3 4]</dd>
</dl>
<h4>2.3 Data Mutators</h4>
<dl>
<dt><code>setitem <var>index</var> <var>array</var> <var>value</var></code>
<dd>Sets the indexth item of the array to value (circular arrays prevented)
<dd class=example>make "a { 1 2 3 } setitem 2 :a "x show :a</dd>
<dt><code>mdsetitem [<var>index</var>...] <var>array</var> <var>value</var></code>
<dd>Sets an item in a multi-dimensional array to value (circular arrays prevented)
<dd class=example>make "a {{1 2} {3 4}} mdsetitem [2 1] :a "x show :a</dd>
<dt><code>.setfirst <var>list</var> <var>value</var></code>
<dd>Sets the first item of the list to value
<dd class=example>make "a [ 1 2 3 ] .setfirst :a "7 show :a</dd>
<dt><code>.setbf <var>list</var> <var>value</var></code>
<dd>Sets the 'butfirst' of the list to the items in value (a list)
<dd class=example>make "a [ 1 2 3 ] .setbf :a [ 4 9 ] show :a</dd>
<dt><code>.setitem <var>index</var> <var>array</var> <var>value</var></code>
<dd>Sets the indexth item of the array to value (circular arrays allowed)
<dd class=example>make "a { 1 2 3 } setitem 2 :a "x show :a</dd>
<dt><code>push <var>stackname</var> <var>thing</var></code>
<dt><code>pop <var>stackname</var></code>
<dd>Push to/pop from a stack i.e. list variable. Stacks grow from the front. Works on words.
<dd class=example>make "s [ 2 1 ] push "s 3 show :s show pop "s</dd>
<dd class=example>make "s "ba push "s "c show :s show pop "s</dd>
<dt><code>queue <var>stackname</var> <var>thing</var></code>
<dt><code>dequeue <var>stackname</var></code>
<dd>Add/remove from a queue i.e. list variable, Queues grow from the end. Works on words.
<dd class=example>make "q [ 1 2 ] queue "q 3 show :q show dequeue "q</dd>
<dd class=example>make "q "ab queue "q "c show :q show dequeue "q</dd>
</dl>
<h4>2.4 Predicates</h4>
<p>Predicates return 1 (true) or 0 (false) </p>
<dl>
<dt><code>wordp <var>thing</var></code>
<dt><code>word? <var>thing</var></code>
<dt><code>listp <var>thing</var></code>
<dt><code>list? <var>thing</var></code>
<dt><code>arrayp <var>thing</var></code>
<dt><code>array? <var>thing</var></code>
<dt><code>numberp <var>thing</var></code>
<dt><code>number? <var>thing</var></code>
<dd>Test if thing is a word, list, array, or number respectively.
<dt><code>emptyp <var>expr</var></code>
<dt><code>empty? <var>expr</var></code>
<dd>Test if thing is an empty list or empty string.
<dt><code>equalp <var>expr</var> <var>expr</var></code>
<dt><code>equal? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> = <var>expr</var></code>
<dt><code>notequalp <var>expr</var> <var>expr</var></code>
<dt><code>notequal? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> <> <var>expr</var></code>
<dd>Equality/inequality tests. Compares strings, numbers, or lists (equal if length and all members are equal).
<dt><code>beforep <var>thing1</var> <var>thing2</var></code>
<dt><code>before? <var>thing1</var> <var>thing2</var></code>
<dd>Test string collation order.
<dt><code>.eq <var>thing1</var> <var>thing2</var></code>
<dd>Test if things have the same identity.
<dt><code>memberp <var>thing</var> <var>list</var></code>
<dt><code>member? <var>thing</var> <var>list</var></code>
<dd>Test if thing is equal to any member of list.
<dt><code>substringp <var>thing1</var> <var>thing2</var></code>
<dt><code>substring? <var>thing1</var> <var>thing2</var></code>
<dd>Test if thing1 is a substring of thing2.
</dl>
<h4>2.5 Queries</h4>
<dl>
<dt><code>count <var>thing</var></code>
<dd>Outputs length of a list or number of characters in a string
<dd class=example>show count [ 1 2 3 ]</dd>
<dd class=example>show count "hello</dd>
<dt><code>ascii <var>expr</var></code>
<dd>Outputs ASCII (actually, Unicode) code point for first character of string
<dd class=example>show ascii "abc</dd>
<dt><code>char <var>expr</var></code>
<dd>Outputs Unicode character at specified code point
<dd class=example>show char 97</dd>
<dt><code>member <var>thing</var> <var>list</var></code>
<dd>Outputs the list (or word) from the first occurence of thing to the end, or empty list (or word)
<dd class=example>show member "a "banana</dd>
<dd class=example>show member 2 [1 2 3 4]</dd>
<dt><code>uppercase <var>expr</var></code>
<dt><code>lowercase <var>expr</var></code>
<dd>Outputs string converted to upper/lowercase
<dd class=example>show uppercase "abc</dd>
<dd class=example>show lowercase "ABC</dd>
<dt><code>standout <var>expr</var></code>
<dd>Outputs string with alphanumeric characters in bold
<dd class=example>show standout "ABCabc123</dd>
<dt><code>parse <var>word</var></code>
<dd>Outputs word parsed as a list.
<dd class=example>show parse "1+2</dd>
<dt><code>runparse <var>word</var></code>
<dd>Outputs word parsed as instructions.
<dd class=example>show runparse "1+2</dd>
</dl>
<h3 id="sec3">3. Communication</h3>
<h4>3.1 Transmitters</h4>
<dl>
<dt><code>print <var>thing</var></code>
<dt><code>pr <var>thing</var></code>
<dt>(<code>print <var>thing1</var> <var>thing2</var> ...)</code>
<dt>(<code>pr <var>thing1</var> <var>thing2</var> ...)</code>
<dd>Print inputs to the text screen, separated by spaces, and followed by a newline.
Square brackets are only put around sublists.
<dd class=example>print "hello</dd>
<dt><code>type <var>thing</var></code>
<dt>(<code>type <var>thing1</var> <var>thing2</var> ...)</code>
<dd>Like <code>print</code> but with no trailing newline.
<dd class=example>type "hel type "lo</dd>
<dt><code>show <var>thing</var></code>
<dt>(<code>show <var>thing1</var> <var>thing2</var> ...)</code>
<dd>Like <code>print</code> but with square brackets around list inputs.
<dd class=example>show "hello</dd>
</dl>
<h4>3.2 Receivers</h4>
<dl>
<dt><code>readlist</code>
<dt><code>(readlist <var>promptstr</var>)</code>
<dd>Prompt the user for a line of input. The result is a list of words.
<dd class=example>show readlist</dd>
<dd class=example>make "colors (readlist [Type some colors:]) show :colors</dd>
<dt><code>readword</code>
<dt><code>(readword <var>promptstr</var>)</code>
<dd>Prompt the user for a line of input. The result (including spaces) is the single word output.
<dd class=example>show readword</dd>
<dd class=example>make "name (readword [What is your name?]) show :name</dd>
</dl>
<!--
<h4>3.3 File Access</h4>
<dl>
</dl>
-->
<h4>3.4 Terminal Access</h4>
<dl>
<dt><code>cleartext</code>
<dt><code>ct</code>
<dd>Clear the text screen.
<dt><code>settextcolor <var>color</var></code>
<dd>Change the text color.
<dt><code>textcolor</code>
<dd>Output the current text color.
<dt><code>increasefont</code>
<dt><code>decreasefont</code>
<dd>Increase/decrease the text size.
<dt><code>settextsize <var>height</var></code>
<dd>Change the text size (in pixels).
<dt><code>textsize</code>
<dd>Output the current text size (in pixels).
<dt><code>setfont <var>name</var></code>
<dd>Change the text font.
<dt><code>font</code>
<dd>Output the current text font.
</dl>
<h3 id="sec4">4. Arithmetic</h3>
<h4>4.1 Numeric Operations</h4>
<p>Inputs are numbers or numeric expressions, output is a number.</p>
<dl>
<dt><code>sum <var>expr</var> <var>expr</var></code>
<dt><code>(sum <var>expr</var> <var>...</var>)</code>
<dt><code><var>expr</var> + <var>expr</var></code>
<dt><code>difference <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> - <var>expr</var></code>
<dt><code>product <var>expr</var> <var>expr</var></code>
<dt><code>(product <var>expr</var> <var>...</var>)</code>
<dt><code><var>expr</var> * <var>expr</var></code>
<dt><code>quotient <var>expr</var> <var>expr</var></code>
<dt><code>(quotient <var>expr</var>)</code>
<dt><code><var>expr</var> / <var>expr</var></code>
<dt><code>power <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> ^ <var>expr</var></code>
<dd>
Add, subtract, multiply, divide, and raise-to-the-power-of respectively.
A single input to quotient returns the reciprocal.
<dt><code>remainder <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> % <var>expr</var></code>
<dt><code>modulo <var>expr</var> <var>expr</var></code>
<dd>
Outputs the remainder (modulus). For <code>remainder</code> and <code>%</code>
the result has the same sign as the first input; for <code>modulo</code> the
result has the same sign as a the second input.
<dt><code>minus <var>expr</var></code>
<dt><code>- <var>expr</var></code>
<dd>
Unary minus sign must begin a top-level expression, follow an infix
operator, or have a leading space and no trailing space.
<dt><code>abs <var>num</var></code>
<dd>Absolute value
<dt><code>int <var>num</var></code>
<dt><code>round <var>num</var></code>
<dd>Truncate or round a number, respectively.
<dt><code>sqrt <var>expr</var></code>
<dt><code>exp <var>expr</var></code>
<dt><code>log10 <var>expr</var></code>
<dt><code>ln <var>expr</var></code>
<dd>Square root, <i>e</i> to the power of, common logarithm, and natural logarithm, respectively.
<dt><code>arctan <var>expr</var></code>
<dt><code>(arctan <var>x</var> <var>y</var>)</code>
<dt><code>sin <var>expr</var></code>
<dt><code>cos <var>expr</var></code>
<dt><code>tan <var>expr</var></code>
<dd>The usual trig functions. Angles are in degrees.
<dt><code>radarctan <var>expr</var></code>
<dt><code>(radarctan <var>x</var> <var>y</var>)</code>
<dt><code>radsin <var>expr</var></code>
<dt><code>radcos <var>expr</var></code>
<dt><code>radtan <var>expr</var></code>
<dd>The usual trig functions. Angles are in radians.
<dt><code>iseq <var>first</var> <var>last</var></code>
<dd>Outputs a list with integers from <var>first</var> to <var>last</var>, inclusive
<dd class=example>show iseq 1 10</dd>
<dt><code>rseq <var>first</var> <var>last</var> <var>count</var></code>
<dd>Outputs a list of <var>count</var> numbers from <var>first</var> to <var>last</var>, inclusive
<dd class=example>show rseq 1 9 5</dd>
</dl>
<h4>4.2 Numeric Predicates</h4>
<dl>
<dt><code>lessp <var>expr</var> <var>expr</var></code>
<dt><code>less? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> < <var>expr</var></code>
<dt><code>greaterp <var>expr</var> <var>expr</var></code>
<dt><code>greater? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> > <var>expr</var></code>
<dt><code>lessequalp <var>expr</var> <var>expr</var></code>
<dt><code>lessequal? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> <= <var>expr</var></code>
<dt><code>greaterequalp <var>expr</var> <var>expr</var></code>
<dt><code>greaterequal? <var>expr</var> <var>expr</var></code>
<dt><code><var>expr</var> >= <var>expr</var></code>
<dd>Less than, greater than, less than or equal to, greater than or equal to,
respectively. Inputs are numbers or numeric expressions, output is 1 (true) or 0 (false).
</dl>
<h4>4.3 Random Numbers</h4>
<dl>
<dt><code>random <var>expr</var></code>
<dt><code>(random <var>start</var> <var>end</var>)</code>
<dd>Outputs a random number from 0 through one less than <var>expr</var>, or from start to end inclusive.
<dd class=example>show random 10</dd>
<dd class=example>show (random 1 6)</dd>
<dt><code>rerandom</code>
<dt>(<code>rerandom <var>expr</var>)</code>
<dd>Reseeds the random number generator, either to a fixed value or the specified seed.
</dl>
<h4>4.4 Print Formatting</h4>
<dl>
<dt><code>form <var>expr</var> <var>width</var> <var>precision</var></code>
<dd>Outputs a formatted string with the result of a numeric expression with <var>precision</var> decimal places and
padded on the left with spaces (if necessary) to be at least <var>width</width> characters long.
<dd class=example>show form 1/3 10 3</dd>
</dl>
<h4>4.5 Bitwise Operations</h4>
<dl>
<dt><code>bitand <var>expr</var> <var>expr</var></code>
<dt><code>(bitand <var>expr</var> ...)</code>
<dt><code>bitor <var>expr</var> <var>expr</var></code>
<dt><code>(bitor <var>expr</var> ...)</code>
<dt><code>bitxor <var>expr</var> <var>expr</var></code>
<dt><code>(bitxor <var>expr</var> ...)</code>
<dt><code>bitnot <var>expr</var></code>
<dd>Bitwise and, or, exclusive-or, and not, respectively.
<dt><code>ashift <var>expr</var> <var>bitcount</var></code>
<dd>Arithmetic bit shift. If bitcount is negative, shifts to the right, preserving sign.
<dt><code>lshift <var>expr</var> <var>bitcount</var></code>
<dd>Logical bit shift. If bitcount is negative, shifts to the right, zero-filling.
</dl>
<h3 id="sec5">5. Logical Operations</h3>
<dl>
<dt><code>true</code>
<dd>Outputs 1
<dt><code>false</code>
<dd>Outputs 0
<dt><code>and <var>expr</var> <var>expr</var></code>
<dt><code>(and <var>expr</var> <var>...</var>)</code>
<dt><code>or <var>expr</var> <var>expr</var></code>
<dt><code>(or <var>expr</var> <var>...</var>)</code>
<dt><code>xor <var>expr</var> <var>expr</var></code>
<dt><code>(xor <var>expr</var> <var>...</var>)</code>
<dt><code>not <var>expr</var></code>
<dd>Logical "and", "or", "exclusive-or", and "not", respectively.
Inputs are numbers or numeric expressions, output is 1 (true) or 0 (false).
</dl>
<h3 id="sec6">6. Graphics</h3>
<p>An introduction to <a target="_blank" href="https://www.cs.berkeley.edu/~bh/v1ch10/turtle.html">Turtle Geometry</a>.</p>
<h4>6.1 Turtle Motion</h4>
<dl>
<dt><code>forward <var>expr</var></code>
<dt><code>fd <var>expr</var></code>
<dd>Move turtle forward <var>expr</var> pixels
<dd class=example>fd 100</dd>
<dt><code>back <var>expr</var></code>
<dt><code>bk <var>expr</var></code>
<dd>Move turtle backward <var>expr</var> pixels
<dd class=example>bk 100</dd>
<dt><code>left <var>expr</var></code>
<dt><code>lt <var>expr</var></code>
<dd>Rotate <var>expr</var> degrees counterclockwise
<dd class=example>lt 90</dd>
<dt><code>right <var>expr</var></code>
<dt><code>rt <var>expr</var></code>
<dd>Rotate <var>expr</var> degrees clockwise
<dd class=example>rt 90</dd>
<dt><code>setpos [ <var>expr</var> <var>expr</var> ]</code>
<dt><code>setxy <var>expr</var> <var>expr</var></code>
<dt><code>setx <var>expr</var></code>
<dt><code>sety <var>expr</var></code>
<dd>Move turtle to the specified location
<dd class=example>setpos [ 100 -100 ]</dd>
<dd class=example>setxy -100 100</dd>
<dt><code>setheading <var>expr</var></code>
<dt><code>seth <var>expr</var></code>
<dd>Rotate the turtle to the specified heading
<dd class=example>setheading 45</dd>
<dt><code>home</code>
<dd>Moves the turtle to center, pointing upwards
<dt><code>arc <var>angle</var> <var>radius</var></code>
<dd>Without moving the turtle, draws an arc centered on the turtle, starting at the turtle's heading.
<dd class=example>arc 180 100</dd>
</dl>
<h4>6.2 Turtle Motion Queries</h4>
<dl>
<dt><code>pos</code>
<dt><code>xcor</code>
<dt><code>ycor</code>
<dd>Outputs the current turtle position as [ x y ], x or y respectively
<dd class=example>show pos</dd>
<dt><code>heading</code>
<dd>Outputs the current turtle heading
<dd class=example>show heading</dd>
<dt><code>towards [ <var>expr</var> <var>expr</var> ]</code>
<dd>Outputs the heading towards the specified [ x y ] coordinates
<dd class=example>show towards [ 0 0 ]</dd>
<dt><code>scrunch</code>
<dd>Outputs the current graphics scaling factors
<dd class=example>show scrunch</dd>
<dt><code>bounds</code>
<dd>Outputs the current graphics screen bounds [ xmin xmax ymin ymax ]
<dd class=example>show bounds</dd>
</dl>
<h4>6.3 Turtle and Window Control</h4>
<dl>
<dt><code>showturtle</code>
<dt><code>st</code>
<dd>Show the turtle
<dt><code>hideturtle</code>
<dt><code>ht</code>
<dd>Hide the turtle
<dt><code>clean</code>
<dd>Clear the drawing area
<dt><code>clearscreen</code>
<dt><code>cs</code>
<dd>Same as clean and home together
<dt><code>wrap</code>
<dd>If the turtle moves off the edge of the screen it will continue on the other side.
(default)
<dt><code>window</code>
<dd>The turtle can move past the edges of the screen, unbounded.
<dt><code>fence</code>
<dd>If the turtle attempts to move past the edge of the screen it will stop.
<dt><code>fill</code>
<dd>Does a paint bucket flood fill at the turtle's position.
<dd class=example>arc 360 100 fill</dd>
<dt><code>filled <var>fillcolor</var> [ <var>statements ...</var> ]</code>
<dd>Execute <var>statements</var> without drawing but keeping track of turtle movements.
When complete, fill the region traced by the turtle with <var>fillcolor</var>
and outline the region with the current pen style.
<dd class=example>filled "red [ repeat 5 [ fd 100 rt 144 ] ]</dd>
<dt><code>label <var>expr</var></code>
<dd>Draw a word (same logic as <code>print</code>) on the graphics display at the turtle location
<dd class=example>repeat 8 [ label "Logo rt 45 ]</dd>
<dt><code>setlabelheight <var>expr</var></code>
<dd>Set the height for text drawn by <code>label</code>, in pixels
<dd class=example>setlabelheight 100 label "Logo</dd>
<dt><code>setlabelfont <var>expr</var></code>
<dd>Set the font for text drawn by <code>label</code>
<dd class=example>setlabelfont "Times\ New\ Roman label "Logo</dd>
<dt><code>setscrunch <var>sx</var> <var>sy</var></code>
<dd>Set the graphics scaling factors
<dd class=example>setscrunch 1 2 arc 360 100</dd>
<dt><code>setturtle <var>index</var></code>
<dd>Switch to the turtle numbered <var>index</var> (starting from 1 for the default turtle present at start).
If the turtle has not been used yet, it will be created at the center, facing upwards, visible, with the pen down.
<dd class=example>setturtle 2 rt 90 fd 100</dd>
<dt><code>ask <var>turtleindex</var> [ <var>statements ...</var> ]</code>
<dd>Execute <var>statements</var> as turtle number <var>turtleindex</var>.
<dd class=example>ask 2 [ rt 90 fd 100 ]</dd>
<dt><code>clearturtles</code>
<dd>Remove all turtles, keeping the current one as index 1.
<dd class=example>fd 50 setturtle 2 rt 90 fd 100 clearturtles </dd>
</dl>
<h4>6.4 Turtle and Window Queries</h4>
<dl>
<dt><code>shownp</code>
<dt><code>shown?</code>
<dd>Outputs 1 if the turtle is shown, 0 if the turtle is hidden
<dt><code>turtlemode</code>
<dd>Outputs <code>WRAP</code>, <code>WINDOW</code> or <code>FENCE</code>
<dt><code>labelsize</code>
<dd>Outputs the height of text drawn by <code>label</code>, in pixels
<dt><code>labelfont</code>
<dd>Outputs the name of the font drawn by <code>label</code>
<dt><code>turtle</code>
<dd>Outputs the index of the currently-active turtle
<dt><code>turtles</code>
<dd>Outputs the largest index that has been passed to <code>setturtle</code>
</dl>
<h4>6.5 Pen and Background Control</h4>
<dl>
<dt><code>pendown</code>
<dt><code>pd</code>
<dd>Turtle resumes leaving a trail
<dt><code>penup</code>
<dt><code>pu</code>
<dd>Turtle stops leaving a trail
<dt><code>penpaint</code>
<dt><code>ppt</code>
<dt><code>penerase</code>
<dt><code>pe</code>
<dt><code>penreverse</code>
<dt><code>px</code>
<dd>Change the turtle drawing mode -
<em>paint</em> (the default) leaves a colored trail,
<em>erase</em> restores the background,
<em>reverse</em> inverts the background.
<dd class=example>setpw 10 px repeat 5 [ fd 100 rt 144 ]</dd>
<dt><code>setpencolor <var>logocolor</var></code>
<dt><code>setpencolor <var>csscolor</var></code>
<dt><code>setpencolor [<var>r</var> <var>g</var> <var>b</var>]</code>
<dd>Set pen/text color. Color can be a standard Logo color number (0-15), CSS color string (<a target="_blank" href="https://www.w3.org/TR/css3-color/">CSS color names or #rrggbb</a>), or in the list version, r/g/b values in 0...99.
<dd>The standard Logo colors are:
<style>
#colortable td { width: 25%; padding-left: 4px; padding-right: 4px; text-align: center; }
</style>
<table id="colortable">
<tr>
<td style="background-color: black; color: white;">0<br>black
<td style="background-color: blue;">1<br>blue
<td style="background-color: lime;">2<br>green
<td style="background-color: cyan;">3<br>cyan
<tr>
<td style="background-color: red;">4<br>red
<td style="background-color: magenta;">5<br>magenta
<td style="background-color: yellow;">6<br>yellow
<td style="background-color: white;">7<br>white
<tr>
<td style="background-color: brown;">8<br>brown
<td style="background-color: tan;">9<br>tan
<td style="background-color: green;">10<br>green
<td style="background-color: aquamarine;">11<br>aqua
<tr>
<td style="background-color: salmon;">12<br>salmon
<td style="background-color: purple;">13<br>purple
<td style="background-color: orange;">14<br>orange
<td style="background-color: gray;">15<br>gray
</table>
<dd class=example>setpencolor 4</dd>
<dd class=example>setpencolor "red</dd>
<dd class=example>setpencolor "#ff0000</dd>
<dd class=example>setpencolor [ 99 0 0 ]</dd>
<dt><code>setpalette <var>colornumber</var> <var>csscolor</var></code>
<dt><code>setpalette <var>colornumber</var> [<var>r</var> <var>g</var> <var>b</var>]</code>
<dd>Change one of the standard color entries (8 or above) to the given color.</dd>
<dd class=example>setpalette 8 "pink setbg 8</dd>
<dd class=example>setpalette 8 "#ff4f00 setbg 8</dd>
<dd class=example>setpalette 8 [ 99 31 0 ] setbg 8</dd>
<dt><code>setpensize <var>expr</var></code>
<dd>Set pen width in pixels. If <var>expr</var> is a list, the first member is used.
<dt><code>setbackground <var>color</var></code>
<dt><code>setscreencolor <var>color</var></code>
<dt><code>setsc <var>color</var></code>
<dd>Set the background color; same options as <code>setpencolor</code>
<dd class=example>setbackground "red</dd>
</dl>
<h4>6.6 Pen Queries</h4>
<dl>
<dt><code>pendownp</code>
<dt><code>pendown?</code>
<dd>Outputs 1 if the pen is down, 0 otherwise
<dd class=example>show pendown?</dd>
<dt><code>penmode</code>
<dd>Outputs <code>PAINT</code>, <code>ERASE</code> or <code>REVERSE</code>
<dd class=example>show penmode</dd>
<dt><code>pencolor</code>
<dt><code>pc</code>
<dd>Outputs the current pen color. This will be a CSS color string, not necessarily the value passed in.
<dd class=example>show pencolor</dd>
<dt><code>palette <var>colornumber</var></code>
<dd>Outputs the a palette entry. This will be a CSS color string, not necessarily the value passed in.</dd>
<dd class=example>show palette 8</dd>
<dt><code>pensize</code>
<dd>Outputs a two element list with the pen width and height (usually the same).
<dd class=example>show pensize</dd>
<dt><code>background</code>
<dt><code>bg</code>
<dt><code>getscreencolor</code>
<dt><code>getsc</code>
<dd>Outputs the background color. This will be a CSS color string, not necessarily the value passed in.
<dd class=example>show background</dd>
</dl>
<!--
<h4>6.7 Saving and Loading Pictures</h4>
-->
<h4>6.7 Bitmap Operations</h4>
<dl>
<dt><code>bitcut <var>width</var> <var>height</var></code>
<dd>Copy a bitmap, from the turtle's position <var>width</var> by <var>height</var> pixels.
<dt><code>bitpaste</code>
<dd>Paste the previously copied bitmap at the current turtle position.
<dd class=example>repeat 4 [ rt 90 fd 40 ] bitcut 50 50 pu fd 100 bitpaste</dd>
</dl>
<h4>6.8 Mouse/Touch Queries</h4>
<dl>
<dt><code>mousepos</code></dt>
<dd>Outputs a list of the x, y coordinates of the last mouse position</dd>
<dd class=example>forever [setpos mousepos]</dd>
<dt><code>clickpos</code></dt>
<dd>Outputs a list of the x, y coordinates of the last mouse press</dd>
<dd class=example>forever [setpos clickpos]</dd>
<dt><code>buttonp</code></dt>
<dt><code>button?</code></dt>
<dd>Outputs 1 if any mouse button is down, 0 otherwise.</dd>
<dd class=example>forever [ifelse button? [pd] [pu] setpos mousepos]</dd>
<dt><code>button</code></dt>
<dd>Outputs a number indicating the pressed mouse buttons
(<code>1</code> = left, 2 = right, etc) or 0 for none.
<dt><code>touches</code></dt>
<dd>Outputs a list of current touch coordinates</dd>
<dd class=example>forever [ifelse count touches [setpos first touches pendown] [penup]]</dd>
</dl>
<h3 id="sec7">7. Workspace Management</h3>
<h4>7.1 Procedure Definition</h4>
<dl>
<dt><code>to <var>procname</var> <var>inputs ...</var> <var>statements ...</var> end</code>
<dd>Define a new named procedure. Inputs can be:
<ul>
<li>Required: <code>:a :b</code></li>
<li>Optional (with default values): <code>[:c 5] [:d 7]</code></li>
<li>Rest (remaining inputs as a list): <code>[:r]</code></li>
<li>Default number of inputs: <code>3</code>
</ul>
<dd class=example>to star :n repeat 5 [ fd :n rt 144 ] end</dd>
<dt><code>define <var>procname</var> [[<var>inputs</var> ...][<var>statements</var> ...]]</code>
<dd>Define a new named procedure with optional inputs
<dd class=example>define "star [[n][repeat 5 [fd :n rt 144]]]</dd>
<dt><code>def <var>procname</var></code>
<dd>Outputs the definition of a named procedure as a string
<dd class=example>show def "star</dd>
<dt><code>text <var>procname</var></code>
<dd>Outputs the definition of a named procedure as a list, suitable for use with <code>DEFINE</code>
<dd class=example>show text "star</dd>
<dt><code>copydef <var>newname</var> <var>oldname</var></code>
<dd>Copy a procedure. If a procedure <var>newname</var> already existed it will
be overridden. Primitive procedures can't be overridden unless <code>REDEFP</code> is <code>TRUE</code>.
<dd class=example>copydef "new "old</dd>
</dl>
<h4>7.2 Variable Definition</h4>
<dl>
<dt><code>make <var>varname</var> <var>expr</var></code>
<dd>Update a variable or define a new global variable. The variable name must
be quoted
<dd class=example>make "myvar 5</dd>
<dt><code>name <var>expr</var> <var>varname</var></code>
<dd>Like <code>make</code> but with the inputs reversed
<dd class=example>name 5 "myvar</dd>
<dt><code>local <var>varname</var></code>
<dt><code>(local <var>varname</var> ...)</code>
<dd>A subsequent <code>make</code> will create the variable(s) in the local scope instead of the global scope
<dd class=example>local "myvar</dd>
<dt><code>localmake <var>varname</var> <var>expr</var></code>
<dd>Define a variable in the local scope (shortcut for <code>local</code> then <code>make</code>
<dd class=example>localmake "myvar 5</dd>
<dt><code>thing <var>varname</var></code>
<dd>Outputs the value of variable. <code>:foo</code> is a shortcut for <code>thing "foo</code>
<dd class=example>show thing "myvar</dd>
<dt><code>global <var>varname</var></code>
<dd>Reserve the variable at the global scope. This doesn't do anything useful.
<dd class=example>global "myvar</dd>
</dl>
<h4>7.3 Property Lists</h4>
<dl>
<dt><code>pprop <var>plistname</var> <var>propname</var> <var>value</var></code>
<dd>Set the property <var>propname</var> in the property list <var>plistname</var> to value <var>value</value>.
<dt><code>gprop <var>plistname</var> <var>propname</var></code>
<dd>Get the value of the property <var>propname</var> in the property list <var>plistname</var>, or the empty list if no such property.
<dt><code>remprop <var>plistname</var> <var>propname</var></code>
<dd>Remove the property <var>propname</var> in the property list <var>plistname</var>.
<dt><code>plist <var>plistname</var></code>
<dd>Return a list of properties in the property list <var>plistname</var>, alternating property name, property value.
</dl>
<h4>7.4 Workspace Predicates</h4>
<p>Predicates return 1 (true) or 0 (false) </p>
<dl>
<dt><code>procedurep <var>name</var></code>
<dt><code>procedure? <var>name</var></code>
<dd>Test if there is a procedure with the given name.
<dt><code>primitivep <var>name</var></code>
<dt><code>primitive? <var>name</var></code>
<dd>Test if there is a built-in procedure with the given name.
<dt><code>definedp <var>name</var></code>
<dt><code>defined? <var>name</var></code>
<dd>Test if there is a user-defined procedure with the given name.
<dt><code>namep <var>name</var></code>
<dt><code>name? <var>name</var></code>
<dd>Test if there is a variable with the given name.
<dt><code>plistp <var>name</var></code>
<dt><code>plist? <var>name</var></code>
<dd>Test if there is a property list with the given name.
</dl>
<h4>7.5 Workspace Queries</h4>
<dl>
<dt><code>contents</code>
<dd>Outputs a list with three members. The first is a list of user-defined procedure names.
The second is a list of defined variables. The third is a list of non-empty property list names.
Only non-buried procedures, variables, and property lists are included.
<dt><code>buried</code>
<dd>Outputs a list with three members. The first is a list of user-defined procedure names
The second is a list of defined variables. The third is a list of non-empty property list names.
Only buried procedures, variables, and property lists are included.
<dt><code>procedures</code>
<dd>Outputs a list of user-defined non-buried procedure names.
<dt><code>primitives</code>
<dd>Outputs a list of primitive non-buried procedure names.
<dt><code>globals</code>
<dd>Outputs a list of defined non-buried global variables.
<dt><code>names</code>
<dd>Outputs a list with two members. The first is an empty list.
The second is a list of defined non-buried variables.
<dt><code>plists</code>
<dd>Outputs a list with three members. The first is an empty list.
The second is an empty list. The third is a list of non-empty non-buried property list names.
<dt><code>namelist <var>name</var></code>
<dt><code>namelist <var>namelist</var></code>
<dd>Return a <code>contents</code>-style list with the given variable names.
<dt><code>pllist <var>plname</var></code>
<dt><code>pllist <var>plnamelist</var></code>