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September 2017 Update

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Ingy döt Net 2017-09-23 10:01:46 +02:00
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33
Task/Call-a-function/ALGOL-68/call-a-function.alg
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@ -1,21 +1,31 @@
# A function without arguments: #
f();
# or #
# 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);
# ALGOL 68 does not support optional arguments, variable numbers of arguments, or named
arguments.
However, some functions may take an argument "0" as an instruction to use the default value
(sort of a pseudo-optional argument). #
# 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,
both ALGOL examples above are already in a statement context.
For full ALGOL compatibility, though, they should be in the form "VOID (f ());" #
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);
@ -26,3 +36,4 @@ x := f(y);
# 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... #