OptionTable ==> Function -- attaching options to a function

OptionTable ==> Function -- attaching options to a function

Synopsis:

Usage: g = defs ==> fun

Operator: ==> -- a binary operator

Input:

defs, an instance of class OptionTable: a hash table whose keys are the names of the optional arguments, and whose values are the corresponding default values.

fun, an instance of class Function: a function that expects optional arguments.

Output:

g, an instance of class Function: a new function that pre-processes the optional arguments and then calls fun.

The new function g works as follows. The value of g args, say, is obtained by evaluation of (fun opts)(args'), where args' is obtained from args by removing the options of the form X=>A (where X is a name of an optional argument), and opts is a hash table of the same form as defs in which the default values have been replaced by the user-supplied values, e.g., the value stored under the key X has been replaced by A.

Remark: defs can also be simply a list of options.

In the following example we use a simple definition for fun so we can see everything that fun receives.

i1 : g = {a=>1, b=>2} ==> opts -> args -> {args, opts}



o1 = g



o1 : Function

i2 : g x



o2 = {x, OptionTable{a => 1}}

                     b => 2



o2 : List

i3 : g(x,y,b=>66)



o3 = {(x, y), OptionTable{a => 1 }}

                          b => 66



o3 : List

i4 : g(t,u,a=>44,b=>77)



o4 = {(t, u), OptionTable{a => 44}}

                          b => 77



o4 : List

OptionTable -- the class of hash tables for optional arguments

Option -- the class of all pairs x => y

=> -- produce an Option

Code:

     -- ../../../Macaulay2/m2/option.m2:31-38
       (defaults,f) -> (
          args -> (
            -- Common code for functions created with ==> to
            -- process options and arguments.
            f ## override (defaults,args)
            )
          )
       )