Singular Manual: Parameter list

3.7.2 Parameter list

Syntax:

( )
( parameter_definition )

Purpose:

Defines the number, type and names of the arguments of a procedure.
The parameter_list is optional.
Adding list # as argument to a parameter list means to allow optional parameters. Furthermore, (list #) is the default for a parameter list (in case no list is explicitly given). Inside the procedure body, the arguments of list # are referenced by #[1], #[2], etc.
If a procedure has optional parameters, the attribute default_arg gives the default values for the optional arguments. This provides in particular the possibility to also change the behaviour of all procedures nested inside the given procedure.

Example:

proc x0
{
    // can be called with
... // any number of arguments of any type: #[1], #[2],...
    // number of arguments: size(#)
}

proc x1 ()
{
... // can only be called without arguments
}

proc x2 (ideal i, int j)
{
... // can only be called with 2 arguments,
    // which can be converted to ideal resp. int
}

proc x3 (i,j)
{
... // can only be called with 2 arguments
    // of any type
    // (i,j) is the same as (def i,def j)
}

proc x5 (i,list #)
{
... // can only be called with at least 1 argument
    // number of arguments: size(#)+1
}

attrib(x5,"default_arg",3);
x5(2); // is equivalent to
x5(2,3);

Note:

The parameter_list may stretch across multiple lines.
A parameter may have any type (including the types proc and ring).
If a parameter is of type ring, then it can only be specified by name, but not with a type. For instance:

proc x6 (r)
{
... // this is correct, r may be of any type, even of type ring
}

proc x7 (ring r)
{
... // this is NOT CORRECT
}

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