The most commonly used form of template is the "explicit-slot" form, which is sometimes called the "question mark" form.
Example:
SHOW MAP [? * ?] [2 3 4 5]
[4 9 16 25]
In this example, MAP evaluates the template [? * ?]
repeatedly, with each of the members of the data list [2 3 4 5]
substituted in turn for the question marks.
The same value was used for every question mark in a given evaluation.
Some tools allow for more than one datum to be substituted in parallel; in these cases the slots are indicated by ?1
for the first datum, ?2
for the second, and so on.
Example:
SHOW (MAP [(WORD ?1 ?2 ?1)] [a b c] [d e f])
[ada beb cfc]
If the template wishes to compute the datum number, the form (? 1)
is equivalent to ?1
, so (? ?1)
means the datum whose number is given in datum number 1.
Some tools allow additional slot designations, as shown in the individual descriptions.