Excerpt from A High Level Real-Time Programming Language: October, 1984 Introduction We present here an outline of a robot programming language, COAL (COntinuous Action Language), together with a formal semantics. COAL is designed to support an abstraction of programming which can operate in a continuous fashion. Variables can change values continuously over time, execution can be instantaneously interrupted in response to an event, and so on. Such constructs must be implemented in terms of discrete steps, but COAL expresses the idealization behind the implementation, in the way that real arithmetic is the idealization behind floating point arithmetic. In this paper, we will describe the basic elements of COAL, define a formal semantics, and present a few typical programming examples. We have not yet addressed the question of implementation. 2. Overview of COAL 2.

1. Variables: COAL supports at least the following types of variables: booleans, integers, real valued vectors (elements of R ), continuous functions from R to R (called "real functions"), and integer semaphores. Certain global variables will be bound to the input and output devices of the particular robotic system. Sensor variables are associated with particular sensors. At each moment in time, the value of the variable is the current measurement of the sensor. Effector variables are associated with parameters of the robot's effectors. Changing the value of the variable causes a motion by the robot. Effector variables must therefore be generally changed continuously.

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