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mapcar
Function
mapcar
is a function that calls its first argument with each
element of its second argument, in turn. The second argument must be
a sequence.
The `map' part of the name comes from the mathematical phrase, `mapping over a domain', meaning to apply a function to each of the elements in a domain. The mathematical phrase is based on the metaphor of a surveyor walking, one step at a time, over an area he is mapping. And `car', of course, comes from the Lisp notion of the first of a list.
For example,
(mapcar '1+ '(2 4 6)) => (3 5 7) |
The function 1+
which adds one to its argument, is executed on
each element of the list, and a new list is returned.
Contrast this with apply
, which applies its first argument to
all the remaining.
(See section Readying a Graph, for a explanation of
apply
.)
In the definition of one-fiftieth
, the first argument is the
anonymous function:
(lambda (arg) (/ arg 50)) |
and the second argument is full-range
, which will be bound to
list-for-graph
.
The whole expression looks like this:
(mapcar '(lambda (arg) (/ arg 50)) full-range)) |
See section `Mapping Functions' in The GNU Emacs Lisp Reference Manual, for more about mapcar
.
Using the one-fiftieth
function, we can generate a list in
which each element is one-fiftieth the size of the corresponding
element in list-for-graph
.
(setq fiftieth-list-for-graph (one-fiftieth list-for-graph)) |
The resulting list looks like this:
(10 20 19 15 11 9 6 5 4 3 3 2 2 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 4) |
This, we are almost ready to print! (We also notice the loss of information: many of the higher ranges are 0, meaning that fewer than 50 defuns had that many words or symbols--but not necessarily meaning that none had that many words or symbols.)
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