Tornado

5
Shell
Function Calls
Shell expressions may contain calls to C functions (or C-compatible functions)
whose names have been entered in the system symbol table; they may also contain
function calls to WindSh commands that execute on the host.
The shell executes such function calls in tasks spawned for the purpose, with the
specified arguments and default task parameters; if the task parameters make a
difference, you can call taskSpawn( ) instead of calling functions from the shell
directly. The value of a function call is the 4-byte integer value returned by the
function. The shell assumes that all functions return integers. If a function returns
a value other than an integer, the shell must know the data type being returned
before the function is invoked. This requires a slightly unusual syntax because you
must cast the function, not its return value. For example:
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-> floatVar = ( float ()) funcThatReturnsAFloat (x,y)
The shell can pass up to ten arguments to a function. In fact, the shell always passes
exactly ten arguments to every function called, passing values of zero for any
arguments not specified. This is harmless because the C function-call protocol
handles passing of variable numbers of arguments. However, it allows you to omit
trailing arguments of value zero from function calls in shell expressions.
Function calls can be nested. That is, a function call can be an argument to another
function call. In the following example, myFunc()takes two arguments: the return
value from yourFunc( ) and myVal. The shell displays the value of the overall
expression, which in this case is the value returned from myFunc( ).
myFunc (yourFunc (yourVal), myVal);
Shell expressions can also contain references to function addresses instead of
function invocations. As in C, this is indicated by the absence of parentheses after
the function name. Thus the following expression evaluates to the result returned
by the function myFunc2( ) plus 4:
4 + myFunc2 ( )
However, the following expression evaluates to the address of myFunc2( ) plus 4:
4 + myFunc2
An important exception to this occurs when the function name is the very first item
encountered in a statement. This is discussed in Arguments to Commands, p.180.
Shell expressions can also contain calls to functions that do not have a symbolic
name in the symbol table, but whose addresses are known to you. To do this,
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