It is likely that you want to write programs in the programming language you are learning. You may also want to try some of the examples included in this book and see what really happens. So I will first show you how to write in ATS a single-file program, that is, a program contained in a single file, and compile it and then execute it.
The following example is a program in ATS that prints out (onto the console) the string "Hello, world!" plus a newline before it terminates:
The keyword val initiates a binding between the variable _ (underscore) and the function call print("Hello, world!\n"). However, this binding is never used after it is introduced; its sole purpose is for the call to the print function to get evaluated.The function main0 is a slight variant of another function named main, which is of certain special meaning in ATS. For a programmer who knows the C or Java programming language, I simply point out that the role of main is essentially the same as its counterpart of the same name in C or Java. The keyword implement initiates the implementation of a function whose interface has already been declared elsewhere. Following is the declared interface for main0 in ATS:
which indicates that main0 is a nullary function, that is, a function taking no arguments, and it returns no value (or it returns the void value). The double slash symbol (//) initiates a comment that terminates at the end of the current line.Suppose that you have already installed the ATS programming language system. You can issue the following command-line to generate an executable named hello in the current working directory:
where hello.dats refers to a file containing the above program. The command atscc is essentially a convenience wrapper around the command atsopt, which triggers the process of typechecking and compiling ATS programs. Note that atscc and atsopt may actually be given the names patscc and patsopt, respectively, in certain installations of ATS. The filename extension .dats should not be altered as it has already been assigned a special meaning that the compilation command atscc recognizes. Another special filename extension is .sats, which we will soon encounter.