Make philosophy
Factor handbook > The language > Collections > Making sequences with variables


When to use make
Make is useful for complex sequence construction which is hard to express with sequence combinators and various combinations of utility words.

For example, this example uses make and reads better than a version using utility words:
[ [ left>> , ] [ "+" % center>> % "-" % ] [ right>> , ] tri ] { } make

compare the above to
[ center>> "+" "-" surround ] [ left>> prefix ] [ right>> suffix ] tri

The first one has a similar shape to the eventual output array. The second one has an arbitrary structure and uses three different utilities. Furthermore, the second version also constructs two redundant intermediate sequences, and for longer sequences, this extra copying will outweigh any overhead make has due to its use of a dynamic variable to store the sequence being built.

On the other hand, using make instead of a single call to surround is overkill. The below headings summarize the most important cases where other idioms are more appropriate than make.

Make versus combinators
Sometimes, usages of make are better expressed with Sequence combinators. For example, instead of calling a combinator with a quotation which executes , exactly once on each iteration, often a combinator encapsulating that specific idiom exists and can be used.

For example,
[ [ 42 * , ] each ] { } make

is equivalent to
[ 42 * ] map

[ [ reverse % ] each ] "" make

is equivalent to
[ reverse ] map concat

Utilities for simple make patterns
Sometimes, an existing word already implements a specific make usage. For example, prefix is equivalent to the following, with the added caveat that the below example always outputs an array:
[ , % ] { } make

The existing utility words can in some cases express intent better than a bunch of , and %.

Constructing quotations
Simple quotation construction can often be accomplished using Fried quotations and Compositional combinators.

For example,
[ 2 , , \ + , ] [ ] make

is better expressed as
'[ 2 _ + ]