Alter - Function Summary

Summary:

If a value is not found in a series, append it; otherwise, remove it.

Usage:

alter series value

Arguments:

series - The series argument. (must be: series port)

value - The value argument.

Description:

The ALTER function is a type of data set operation. It either adds or removes a value depending on whether the value is already included. The word ALTER is short for the word "alternate".

For example, let's say you want to keep track of a few options used by your code. The options may be: FLOUR, SUGAR, SALT, and PEPPER. The following code will create a new block (to hold the data set) and add to it:

options: copy [] alter options 'SALT probe options [SALT]

alter options 'SUGAR probe options [SALT SUGAR]

You can use functions like FIND to test the presence of an option in the set:

if find options 'SALT [print "Salt was found"] Salt was found

If you use ALTER a second time for the same option word, it will be removed:

alter options 'SALT probe options [SUGAR]

Normally ALTER values are symbolic words (such as those shown above) but any datatype can be used such as integers, strings, etc.

alter options 120 alter options "test" probe options [SUGAR 120 "test"]

Related:

difference - Return the difference of two data sets.
exclude - Return the first set less the second set.
find - Finds a value in a series and returns the series at the start of it.
intersect - Create a new value that is the intersection of the two arguments.
remove - Removes value(s) from a series and returns after the remove.
unique - Returns a set with duplicate values removed.

User Comments:

-From: giesse_writeme.com 7-Dec-2000/2:41:57-8:00:

NOTE: it returns the head of the list when the value is appended, but returns the position after the removal if the value is removed.