Procedures and Functions

Procedures and functions are distinct objects, although they are defined in about the same way. The difference is used to perform error-checking at runtime: a procedure must not return a value, but a function has to.

The syntax for function and procedure definitions is:

function:   func NAME() stmt

procedure:  proc NAME() stmt

In this syntax, func and proc are keyword and must be entered literally. NAME stand for the name of the function or procedure, respectively. stmt is meant in the sense of the previous section.

When calling functions and procedures, arguments separated by commas can be passed in brackets. These are referenced inside the function or procedure just like in e.g. the bourne shell: $3 is used to reference the third argument. Argument counting starts with 1.

Arguments are passed as values (so arbitrary arithmetic expressions are possible) and are inside the function or procedure semantically equivalent to variables.

To reference an argument with number greater than the number of arguments actually passed, is considered a runtime-error. This makes it possible to construct functions and procedures which accept a variable number of arguments, if a leading argument determines the number of arguments to follow (just like printf()).

Functions and procedures can be used recursively (with a finite depth of the calling stack, however).

As an example, the following defines a recursive implementation of the factorial function in terms of the hoc language:

func fac()
     {
     if ($1 <= 0)
        return 1;
     else
        return $1 * fac($1-1);
     }

There are four predefined procedures in YODA:

init():

init() is called exactly once if the task is loaded.

analyze():

This task is called each time an event matches a selector.

finish():

It is called every time YODA stops, i.e. if stop is pressed or if EOF is encountered.

refresh():

This task is associated with the display and NOT called in batch mode. Using the internal display of YODA, refresh() is called just before each timer triggered update of the display and if YODA stops. By default (see -z option), this is every 15 seconds.

 

Table 5.5: List of Functions for Input and Output of Arrays to Files

Function	Purpose
writevec(arrayName,dim,filename)	write array of name arrayName and dimension dim to ASCII file with name filename.
dumpvec(arrayName,dim,filename)	write array of name arrayName and dimension dim to binary file with name filename.
dumpvecShort(arrayName,dim,filename)	same as dumpvec(...) except that double numbers are converted to short integers before writing (this saves disk space when applicable).
readvec(arrayName,dim,filename)	read ASCII file named filename and fill numbers into the array of name arrayName and dimension dim. Lines beginning with the '#' character are considered to be comments.
sourcevec(arrayName,dim,filename)	read binary file named filename and fill numbers into the array of name arrayName and dimension dim.
writetext(textSelector,text_length,	writes text event selected by textSelector
filename,filemode)	to file filename. The mode may be "w" for a new file or "a" for append. example: select TEXT ;
	writetext(TEXT,TEXT_LENGTH,"test","w");