120 lines
4.5 KiB
Markdown
120 lines
4.5 KiB
Markdown
# Tittle
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Turtles in [Scittle](https://babashka.org/scittle/).
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See [Papert, S: Mindstorms](https://www.worldofbooks.com/en-gb/products/mindstorms-book-seymour-papert-9780745016047).
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## State of Play
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As a proof of concept, this proves the concept. There's a lot more to do.
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I have not (yet) managed to get a scittle REPL running.
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Clojure (and thus Scittle) is a fairly pure functional language. It's not good at imperative things, although of course it can do them. Turtle Graphics is by its nature imperative: you're commanding the turtle. So this is not a very idiomatic use of Scittle, and it's not very efficient; it invites you to write recursive functions (and of course I wish to encourage you to write recursive functions), but recursive functions in Scittle are not fast.
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## Usage
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At this stage, edit `index.html`
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### Functions
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Generally speaking, functions whose names end in exclamation points are imperative functions: they change the state of things by side-effect, and the return value may not be particularly relevant. I would normally consider imperative functions bad practice in Clojure.
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#### (cos *angle*)
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Return the cosine of this `angle`, considered to be expressed in degrees.
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#### (degrees->radians *angle*)
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Return the equivalent, in radians, of this `angle` espressed in degrees.
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#### (draw-polygon! *sides* *side-length*)
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Draw a regular polygon, with this number of `sides`, each of this `side-length`.
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#### (draw-tree *length* *left-branch* *right-branch* *curvature* *branch-fraction* *trunk-fraction* *depth*)
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Draw a tree. This is a fairly crude tree-drawing algorithm; there's lots of ways it can be improved, consider it a plac to start. Parameters (all numeric) as follows:
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* `length`: the length of the current segment of the tree;
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* `left-branch`: the amount to turn left, with respect to the parent segment, to draw a left branch, in degrees;
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* `right-branch`: the amount to turn right, with respect to the parent segment, to draw a right branch, in degrees;
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* `curvature`: the amount to turn to draw the next segment of the current stem, in degrees;
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* `branch-fraction`: the length of a branch segment, as a proportion of the length of its parent segment;
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* `trunk-fraction`: the length of the next segment of a stem, as a proportion of the length of its parent segment;
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* `depth`: the maximum depth of recursion to allow.
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#### (log-turtle!)
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Prints the state of the turtle to the browser console.
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#### (move! *distance*)
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Move the turtle forward on its current heading by `distance` units.
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**NOTE THAT** this function invokes `move-to!`, q.v., which will create a
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line element if the pen is down.
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#### (move-to! *x* *y*)
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Move the turtle absolutely to the coordinates `x`, `y`. If the pen is down, create a line element.
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**NOTE THAT** this is the only function which creates new graphical elements.
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#### (number-or-error! *n*)
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If `n` is a number, return it, else throw an exception.
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#### (pen-down!)
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Put the turtle's pen down (i.e., cause line segments to be created).
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#### (pen-down?)
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Return `true` if the turtle's pen is down, else `false`.
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#### (pen-up!)
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Lift the turtle's pen up (line segments will not be created).
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#### (pen-up?)
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Return `true` if the turtle's pen is not down, else `false`.
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#### (radians->degrees *angle*)
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Return the equivalent, in degrees, of this `angle` espressed in radians.
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#### (sanitise-angle *angle*)
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Take this `angle`, and return a number between 0 and 360 that represents it as an angular measurement.
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#### (set-ink! *colour*)
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Set the ink with which the turtle draws to this `colour`, which should be a string representation of a colour known to CSS.
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#### (sin *angle*)
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Return the sine of this `angle`, considered to be expressed in degrees.
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#### (turn! *angle*)
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Turn the turtle clockwise by this `angle`, expressed in degrees with respect to the X axis. If `angle` is not a number, throw an exception.
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#### (turn-to! *angle*)
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Turn the turtle to face `angle`, expressed in degrees with respect to the X axis. If `angle` is not a number, throw an exception.
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**TODO**: Note that 180° is currently straight up; this is not intended, it is intended that 0° should be straight up, and this change will be made
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before version 1.0.
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## Licence
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Copyright © Simon Brooke 2025
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This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
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