Apifun

            Purpose

The goal of this module is to provide a set to function to check input arguments
in macros.

In functions with a variable number of input arguments,
we often have the following source code, which checks that 
the number of input arguments provided by the user is 
consistent with the number of expected arguments :

[lhs,rhs]=argn()
if ( rhs < 2 | rhs > 5 ) then
  errmsg = msprintf(gettext("%s: Unexpected number of input arguments : %d
provided while from %d to %d are expected."), "myfunction", rhs,2,5);
  error(errmsg)
end

Writing this code is error-prone and boring.
Moreover, this fragment of source code is duplicated in 
many functions, leading to small variations depending on the 
developer.
In particular, this makes the localization of the error messages 
difficult, because the message can be slightly different 
depending on the function.
It can also lead to unexpected errors, for example when the 
string containing the error message is wrongly formatted. 
In this case, instead of the expected error, the user gets a message telling 
that the argument of the msprintf function has a wrong format ; this 
is an information which can let the user confused about the source 
of the error.
Moreover, because writing this source code is boring, many existing functions 
are not sufficiently robust against wrong uses.

The goal of the apifun module is to simplify this task. 
For example, the apifun_checkrhs function checks that the number of 
input arguments provided by the user of the function corresponds 
to the number of expected arguments.
The following function takes 2/3 input arguments and 1 output arguments.

function y = myfunction ( varargin )
  [lhs, rhs] = argn()
  apifun_checkrhs ( "myfunction" , rhs , 2:3 )
  apifun_checklhs ( "myfunction" , lhs , 1 )
  x1 = varargin(1)
  x2 = varargin(2)
  if ( rhs >= 3 ) then
    x3 = varargin(3)
  else
    x3 = 2
  end
  y = x1 + x2 + x3
endfunction

When called with 1 or 4 arguments, an error will be 
generated.

// Calling sequences which work
y = myfunction ( 1 , 2 )
y = myfunction ( 1 , 2 , 3 )
// Calling sequences which generate an error
y = myfunction ( 1 )
y = myfunction ( 1 , 2 , 3 , 4 )

The following session shows the kind of error message which is
produced by the apifun module, for example when the number of input argument is
wrong.
The error message is clear about the function which generates the message (e.g.
"myfunction").

-->y = myfunction ( 1 )
 !--error 10000 
myfunction: Unexpected number of input arguments : 1 provided while the number
of expected input arguments should be in the set [2 3].
at line     131 of function apifun_checkrhs called by :  
at line       3 of function myfunction called by :  
y = myfunction ( 1 )

The advantages of using the current module are the following.
 * Designing robust functions is much simpler which improves both the 
   quality and the robustness of functions.
 * The provided source code is factored into one single 
   module. 
 * It is similar to what is provided to the developers of Scilab gateways,
   at the C level.

The following is a list of the function currently implemented in this module:

The following is a list of the function currently implemented in this module:

 * apifun_overview — An overview of the Apifun toolbox.
 * apifun_checklhs — Generates an error if the number of LHS is not in given
set.
 * apifun_checkrhs — Generates an error if the number of RHS is not in given
set.

Support

 * apifun_argindefault — Returns the value of an input argument.
 * apifun_expandfromsize — Expand variables from a size.
 * apifun_expandvar — Expand variables so that they all have the same shape.
 * apifun_keyvaluepairs — Returns options from key-value pairs.
 
Check content

 * apifun_checkcomplex — Generates an error if the variable has a zero
imaginary part.
 * apifun_checkflint — Generates an error if the variable is not a floating
point integer.
 * apifun_checkgreq — Check that the value is greater or equal than a
threshold.
 * apifun_checkloweq — Checks that the value is lower or equal than a
threshold.
 * apifun_checkoption — Generates an error if the value of an input argument
is not expected.
 * apifun_checkrange — Check that the value is in a given range.
 * apifun_checkreal — Generates an error if the variable has an imaginary
part.
 
Check size

 * apifun_checkdims — Generates an error if the variable has not the required
size.
 * apifun_checkscalar — Generates an error if the variable is not a scalar.
 * apifun_checksquare — Generates an error if the variable is not a square
matrix.
 * apifun_checkveccol — Generates an error if the variable is not a column
vector.
 * apifun_checkvecrow — Generates an error if the variable is not a row
vector.
 * apifun_checkvector — Generates an error if the variable is not a vector.
 
Check type

 * apifun_checkcallable — Generates an error if the variable is not a callable
function.
 * apifun_checktype — Generates an error if the given variable is not of
expected type.