EWD249 - 65

Line Carriage Return) and of a "backspace", the order in which the printable positions have to be served is dictated by the printing commands and, secondly, that this order has nothing to do with the order of the marks if we number them, say, in the order of increasing i. As a result they quickly conclude that the use of storage seems indicated: first the thousand i-values should be scanned, i.e. the page image should be stored in a convenient manner, while afterwards, under control of the stored image, the page should be printed. (To be more precise: we assume that the computer has sufficient store for this purpose and that the computation of the function values "fx(i)" and "fy(i)" may be so time-consuming that we wish to have them computed only once for each i-value.)

We now document this design decision, and I propose the following piece of text:

      COMPFIRST
      begin
      draw: {build; print};
      var image;
      instr build(image), print(image)
      end

The above piece of documentation, which is considered as an integral part of the final program, should be interpreted as follows.

It refers to a machine called "COMPFIRST" (we use capitals for machine names and try to express the type of decision reflected in the program made for them).

The next line gives a named algorithm: its name is "draw" (this being assumed to be the name of the total program to be made, that has to "draw" a curve), the algorithm expresses the desired time-succession of two actions, building the image in store, followed by printing paper under control of the stored value.

In the last two lines we give the declarations (or declaration headings), naming the components of the machine for which the above algorithm is intended. The first line describes that the name "image" will be used for the data structure