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Task/Call-a-function/ALGOL-68/call-a-function.alg

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+# Note functions and subroutines are called procedures (or PROCs) in Algol 68 #
+# A function called without arguments: #
+f;
+# Algol 68 does not expect an empty parameter list for calls with no arguments, "f()" is a syntax error #
+# A function with a fixed number of arguments: #
+f(1, x);
+
+# variable number of arguments: #
+# functions that accept an array as a parameter can effectively provide variable numbers of arguments #
+# a "literal array" (called a row-display in Algol 68) can be passed, as is often the case for the I/O #
+# functions - e.g.: #
+print( ( "the result is: ", r, " after ", n, " iterations", newline ) );
+# the outer brackets indicate the parameters of print, the inner brackets indicates the contents are a "literal array" #
+
+# ALGOL 68 does not support optional arguments, though in some cases an empty array could be passed to a function #
+# expecting an array, e.g.: #
+f( () );
+
+# named arguments - see the Algol 68 sample in: http://rosettacode.org/wiki/Named_parameters #
+
+# In "Talk:Call a function" a statement context is explained as
+"The function is used as an instruction (with a void context),
+rather than used within an expression."
+Based on that, the examples above are already in a statement context.
+Technically, when a function that returns other than VOID (i.e. is not a subroutine)
+is called in a statement context, the result of the call is "voided" i.e. discarded.
+If desired, this can be made explicit using a cast, e.g.: #
+VOID(f);
+
+# A function's return value being used: #
+x := f(y);
+
+# There is no distinction between built-in functions and user-defined functions. #
+
+# A subroutine is simply a function that returns VOID. #
+
+# If the function is declared with argument(s) of mode REF MODE,
+then those arguments are being passed by reference. #
+# Technically, all parameters are passed by value, however the value of a REF MODE is a reference... #