This document describes the development of a programming environment for controlling LEGO Mindstorms NXT robots using the functional reactive programming (FRP) language Yampa. It discusses the reactive programming and FRP concepts used. The programming environment takes input from sensors and sends output to motors via defined data types and modules. The core runs a signal function in a repeating time-based process to dynamically react to inputs over time. Functions were implemented for running, stopping, and interfacing with the NXT inputs and outputs to build a basic but usable programming tool.

1. Development of Programming
Environment for LEGO
Mindstorms NXT by Yampa
Takahiro Ebana
Supervised by Taro Suzuki
University of Aizu

2. Basic knowledges
○Reactive Programming
A programming method that dynamic react to changes of
various informations such as input from user or the
progress of time.
○FRP
a technique to perform Reactive programming with a
functional language.
- Yampa is a FRP language based on Haskell.
○LEGO Mindstorms NXT
the robot teaching material sold by LEGO company.

3. Background
○Why do I use Yampa?
- An FRP language is not so really used
- To show the example which I used an FRP
language for
・
○Why do I use LEGO Mindstorms NXT as a control
object?
- To cancel difficulty of errand of the control that
I used bluetooth for

4. Design of programming environment:
process flow
Process flow step in a time unit:
１, Get input data from LEGO Mindstorms NXT.
２, Convert input data to NXTInput.
３, I hand NXTInput to signal function and run signal
function.
４, Convert NXTOutput to direct commands.
５, Send direct command to LEGO Mindstorms NXT.
６, Go next time unit（Back to step 1）.
A program implemented in Yampa is repetition of this
processing.

5. Design of programming environment:
data structure and modules
Data types
・NXTInput
- The data type that has input from NXT
・NXTOutput
- The data type that has a parameter to transmit to
NXT
・SF NXTInput NXTOutput
- The data type of the main body of program that a user
makes in this programming environment
Modules
・NXTMain
- The centor of this programming environment
・NXTMotorInput/Output, NXTSensorInput
- Control NXT motor and sensor

6. Implemantation:
Run and stop signal function
These functions implemented in NXTMain.
・runNXTProgram
- This function process 3 step:
１, Connect NXT by bluetooth.
２, Run signal function (maked user).
３, Off bluetooth connect.
・endNXTProgram
- The process of signal function is an infinite loop.
- When user want to terminate signal function, use this.

7. Implementation : input
About a function to get input from a motor and a sensor.
The function to get input from LEGO Mindstorms NXT is signal
function basically.
- For example : SF NXTInput Int
There are two types of functions to acquire the input from
motor and sensor.
- Get input from a motor or sensor which specified a port
number for the cause
- Get input from a motor which specified a kind of motor or
sensor for the cause.

8. Implementation : output
The output function performs the output to the motor mainly.
There is the case that is not so when the output function is
Signal function.
- There does not need to be it in signal function if they do
not change output by time.
The procedure of the movement of the output function when I
considered NXT to be a car is as follows.
１, Get input data from left and right wheel.
２, calculation
３, Return output data (NXTOutput)
Because the function to acquire input is signal function, also
this function is signal function.

9. Conclusions
I implemented a function that worked to run of a SF. By this
function, user can make efforts in only making of signal
function.
Also I implemented any functions to operate motor and
sensor easily. By these functions, user can treat motor and
sensor without being conscious of a direct command.
Functions that I implemented this research tend to be basic
function.
- It seems that I can build the programming environment
that is easy to use more by adding more progressive
functions.