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Article contents:== Outdated egg! This is an egg for CHICKEN 3, the unsupported old release. You're almost certainly looking for [[/eggref/4/logo|the CHICKEN 4 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-4.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[toc:]] == logo [[tags: egg]] === Introduction This Scheme code is a small but serious implementation of Logo. It is inspired by Brian Harvey's UCB Logo. No attempt at optimization has been made. There are many optimizations that are easily made; however, the implementation is not properly tail recursive and adding that optimization would be non-trivial. In general, making a dynamically scoped language properly tail recursive is tricky, and even experts have goofed. See [[http://www.accesscom.com/%7Edarius/writings/dynatail.html| Darius Bacon's note]] for a discussion of how to implement both dynamic scope and proper tail recursion. While the syntax and semantics are very similar to UCB Logo, there are some small differences. For example, no line continuation indicators are necessary; carriage returns can be used to format the input. To cause the input to be evaluated, press return on a blank line. Also, the infix operations are not self delimiting. Thus {{2+3}} does not evaluate to a number. Finally, there is no special mode for entering procedures. They can be typed in on one line or many using either the {{To}} special form or the {{Define}} command. === Usage: [procedure] (go-logo) Starts an interactive Logo session. === Sample Interaction Welcome to Arthur Nunes-Harwitt's Classic Logo ?to downup :word print :word if equalp count :word 1 [stop] downup bl :word print :word end ?downup "Hello Hello Hell Hel He H He Hel Hell Hello ?print 2+3i + 4 6+3i ?print count "Hello 5 ?to fact :n if :n = 0 [op 1] op :n * fact :n - 1 end ?print fact 5 120 ?to fib :n if :n < 2 [op 1] op (fib :n - 1) + (fib :n - 2) end ?print fib 4 5 ?print fib 5 8 ?print fib 6 13 ?make "x 0 ?print :x 0 ?repeat 720 [make "x :x + 1] ?print :x 720 === Defined Logo Primitives ==== Math <table> <tr> <td>Sum </td><td>Difference </td><td>Minus </td><td>Product </td><td>Quotient </td></tr> <tr> <td>Power </td><td>Remainder </td><td>Int </td><td>Round </td><td>Abs </td></tr> <tr> <td>Sqrt </td><td>Exp </td><td>ln </td><td>Log10 </td><td>Sin </td></tr> <tr> <td>Cos </td><td>ArcTan </td><td>RadSin </td><td>RadCos </td><td>RadArcTan </td></tr> <tr> <td>Float </td><td>Numerator </td><td>Denominator </td><td>RealPart </td><td>ImagPart </td></tr> </table> ==== Infix <table> <tr> <td>&lt; </td><td>= </td><td>&gt; </td><td>+ </td></tr> <tr> <td>- </td><td>* </td><td>/ </td><td>^ </td></tr> </table> ==== Predicates <table> <tr> <td>GreaterP </td><td>LessP </td><td>EqualP </td><td>IntegerP </td></tr> <tr> <td>FloatP </td><td>RatioP </td><td>ComplexP </td><td>ListP </td></tr> <tr> <td>WordP </td><td>NumberP </td><td>EmptyP </td><td>MemberP </td></tr> <tr> <td>ProcedureP </td><td>PrimitiveP </td><td>DefinedP </td><td>NameP </td></tr> </table> ==== Logical Connectives <table> <tr> <td>Not </td><td>And </td><td>Or </td></tr> </table> ==== Symbolic Processing <table> <tr> <td>First </td><td>Butfirst </td><td>BF </td><td>Fput </td></tr> <tr> <td>Sentence </td><td>SE </td><td>List </td><td>Last </td></tr> <tr> <td>Butlast </td><td>BL </td><td>Lput </td><td>Count </td></tr> <tr> <td>Item </td><td>Ascii </td><td>Char </td><td>Word </td></tr> </table> ==== Control <table> <tr> <td>If </td><td>IfElse </td><td>Repeat </td></tr> <tr> <td>Output </td><td>OP </td><td>Stop </td></tr> <tr> <td>Catch </td><td>Throw </td><td>Run </td></tr> </table> ==== State <table> <tr> <td>Make </td><td>Define </td><td>Text </td></tr> </table> ==== I/O <table> <tr> <td>Print </td><td>Show </td><td>Type </td><td>Readlist </td><td>RL </td></tr> </table> ==== Property Lists <table> <tr> <td>GProp </td><td>RemProp </td><td>PProp </td><td>PList </td></tr> </table> ==== Special Form To ''name'' ''var''* ''command''* end === Author Arthur Nunes-Harwitt === License This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/2.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. Description of your changes:

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