Lego EV3: разница между Small Basic и EV3-Basic

 

Programming a robot to do your bidding is great fun. The easiest way to program the Lego EV3 brick for simple tasks is the graphical programming environment provided by Lego. But for larger and more complex programs, this no longer works and you need some text-based programming language to write programs. There are already many different projects that have created programming environments for the EV3 to provide exactly this (LeJOS, MonoBrick, RobotC, ev3dev, and many more). But they all have one thing in common: They are awfully complicated to set up and use, and you probably need years of computer experience to get any of them working.

To fill the gap between very-easy-to-use but limited and all-powerful but complicated, I have invented EV3-Basic. It is targeted mainly on users that want to go beyond the limitations of graphical programming, but are no IT-professionals themselves. EV3-Basic is quite easy to learn and still offers all functionality you need to create awesome programs. Learning to program on the way is probably an additional benefit.

EV3-Basic is based on the programming language "Small Basic" which was developed by Microsoft to provide an entrance into programming especially for children, but also for all interested persons new to this topic. "Small Basic" is intentionally designed for ease of use, and for my EV3-extension I tried to do the same. I would be very happy, if this language could indeed be of some use to learn programming and to use the EV3 brick more creatively.

 

Lego EV3: разница между Small Basic и EV3-Basic

While I have tried to mimic the original behaviour of Small Basic in my EV3-compiler as exactly as possible, there are some things that simply can not be done with the EV3 byte code interpreter.

Variables are typed

While Small Basic has just one datatype which is a unicode string into which all possible values (even arrays) are mangled, EV3Basic has 4 distinct datatypes for variables:

• Number (a 32bit floating point)
• Text
• Array of Numbers
• Array of Texts

Every variable has one of these types (which is determined by its first use in the program code) and can not be used to store anything else.

Operators and functions work on compile-type types

Arithmetic or logic operators need to be provided with either number or text parameters and deliver a result of also a defined type (for example, the "<" needs two numbers and delivers a text). One exception is the "=" which will perform either a numerical or a textual comparision, depending on the compile-time type of the operands. Another exception is the "+" that will do a numerical add when provided with two numbers, but will do a text concatenation if one of the operands is text. Similar requirements are there for function parameters, which also have a defined compile-time type. To make things easier, an automatic conversion from number to text is done if a parameter needs a text (but not the other way round).

Arrays

In Small Basic arrays work like a dictionary and can use any text as an index. EV3-Basic can not do that. Only numbers are allowed as index and only non-negative numbers without decimal places work as expected (A[4.5] is the same as A[4], A[-4] will always deliver 0 or "") There is no support for multi-dimensional arrays. While arrays can be passed to library functions and out again, no temporary arrays are created to receive the result. For all functions that return an array, this return value must be immediately stored in an array variable.

Limitation for text

Any text variable can only hold up to 251 characters and not the full unicode range is supported, but only the codes 1 - 255 (they are just plain C-style char strings). The same holds for all elements of text arrays.

 

Getting Started

First thing you need is a PC running Microsoft Windows (any version up from Windows XP) and the current version of Microsoft Small Basic which can be downloaded for free. If you are completely new to programming, you probably need to learn the principles first. This does not take all too long and is quite fun in itself. There are some very good tutorials on the Small Basic website to help you with this.

Next step is to download and install the EV3-extension for Small Basic to actually be able to control the EV3 brick with your program. From the newest release of EV3-Basic, download and install the file "EV3BasicInstaller.msi". This should install the extension right into the installation directory of Small Basic. If you have before chosen a non-standard location for Small Basic, use this same location here. At the next start of Small Basic (restart it if it was still running), you have access to various objects to control different aspects of the brick and some additional multi-purpose objects as well. Now create your very first EV3-program by writing

   LCD.Clear()
   LCD.Write(40,40, "Hello EV3")
   Program.Delay(10000)

into the program window. Then connect the EV3 brick with your computer using the USB cable, start it up, and when it is running, press the big blue "Run" button of Small Basic. This will compile and start the program that remote-controls the brick from the PC.

When writing your own programs, the Intellisense - system of Small Basic will show you the possible library functions and usage documentation which contains the same information that is also available in this document in the chapter "Library Documentation". Many more examples for the EV3 programming are also available on the releases page (probably named 'examples.zip').

Remote controlling the brick with a program on the PC is a cool thing, but for many uses you will need an independend robot that has its own program and does not need the PC to tell it every single step.

To get the program to the brick, you need the EV3Explorer which was already installed along with the EV3-extension and is available on the windows start menu (EV3Basic/EV3Explorer). Starting this program will open a window where you can see the files that are stored on the EV3 brick (on the left side of the window) and also the files stored on your PC (on the right side of the window). You can compile any of the examples and your own programs by selecting the source code file (ends with .sb) and click "Compile and Run". This will compile the source code file to a file that can be executed by the brick (having the file extension .rbf), uploads it to the brick and immediately starts it. If you want to start your programs from the menu on the brick, you need to create a subfolder of the "prjs"-folder with a name of your choice and use this as a target folder for compilation. (The EV3 will only show programs in its menu that are properly placed in their own folder).

Quick reference of Small Basic

For persons who already know how to program with some other languages and do not want to go through the complete Small Basic tutorials, here is a short example that contains most language constructs and a short explanation of each. This example will not run on the EV3 brick, because it uses the Small Basic text window.

  ' Demo program explaining most of Small Basic
  ' (all comments start with single quotation mark)
  ' Execution starts here
  A = 5       ' variables are implicitly declared at first use 
  a = a + 1   ' everything is case-insensitive
  B[a] = 55   ' arrays are implicitly defined and grow as needed
  X = "hi"    ' variables can also hold text
  Sub write   ' defines a sub-program with this name (no parameters possible)
	TextWindow.WriteLine(X)           ' call library function, access variable defined elsewere
  EndSub
     ' control flow of the main program runs around the Sub - definitions
  TextWindow.WriteLine("A="+a)        ' string concatenation with +
  WRITE()                             ' call subprogram. name is also case-insensitive
  write2()                            ' may call subprogram that is defined further down the code
  TextWindow.Writeline("B[6]="+B[6])  ' access to arrays'
  
  For i=2 to 5 		               	  ' a loop from 2 to 5 (inclusively)
	TextWindow.Writeline("I:"+I)
  EndFor
  For i=6.5 to 10.5 step 2         	  ' a loop with fractional values and larger step
	TextWindow.Writeline("I:"+I)
  EndFor
  Sub write2
	write()          ' subprogram can call other subprograms
	write()
  EndSub
     ' control flow of the main program runs around the Sub - definitions
   I=99				' case insensitive - overwrites previous i
   while i>3        ' loop with condition
     i=i/2
     TextWindow.Writeline("I:"+i)
   endwhile
   TextWindow.WriteLine("PI="+Math.PI)         ' a library property (access without parentesis)
   TextWindow.WriteLine("SIN="+Math.Sin(0.5))  ' library function returning value
   A=50
   B=20
   If a<5 then				       ' an IF-construct with multiple conditions
		TextWindow.WriteLine("first")
   elseif a<10 and b<100 then                ' logic 'and' of conditions
		TextWindow.WriteLine("second")
   elseif a<20 or (b>40 and b<60) then       ' logic 'or' and nested conditions
		TextWindow.WriteLine("third")
   else
		TextWindow.WriteLine("other")
   endif

 

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