Previously we saw how to define the procedure iscolourword by using partial application to combine member with a list. We can produce another closure, as follows:
If we often wanted to double all the numbers in a list, we could create a new procedure by partially applying list_results to double, and then re-using the new procedure as needed.
To do this we use the partial application brackets "(% ... %)" which have the effect NOT of running a procedure but of creating a NEW procedure that can be run later on with the data between the brackets.
If P is a procedure that requires three numbers to run, then P(% 3, 4 %) is a combination of P and two numbers, which can be run later on if the third number is given.
Similarly the procedure list_results can be partially applied to the procedure double, to create a new procedure that can be run later on if a list is given to be provided as the first argument of list_results. E.g.
vars double_elements = list_results(% double %);or, using a better, but equivalent syntax, which shows more clearly that we are defining a new procedure:
define double_elements = list_results(% double %)
enddefine;
This defines double_elements to be a procedure made from the procedure
list_results by combining it with the procedure double as its "frozen
argument".
We now have a new procedure:
double_elements =>
** <procedure double_elements>
We can apply double_elements to lots of different lists:
double_elements([11 22 33]) =>
** [22 44 66]
double_elements([66.5 103.45 89 77.002 1000000]) =>
** [133.0 206.9 178 154.004 2000000]