First-class functions/Use numbers analogously: Difference between revisions

This seems to satisfy the current problem statement:

<lang j> multiplier=: conjunction def 'm * n * ]'</lang>

<lang j> 2 multiplier 0.5 (4)

4

0.5 multiplier 4 (0.25)

0.5

4 multiplier 0.25 (2+4)

6

0.25 multiplier (2+4) (1%2+4)

0.25

(2+4) multiplier (1%2+4) 2

2</lang>

J uses the concept of ''conjunctions'' to enable the composition of new verbs (functions). Conjunctions can link two verbs as in the [[First-class functions]] problem, analogous to the ''and'' in the phrase "cube and cuberoot". The [[First-class functions]] solution used the primitive conjunction <tt>@</tt> to link two verbs to create a new verb. The solution here uses a user-defined conjunction <tt>multiplier</tt> that links two nouns (numbers in this case) to create a new verb - something like "multiply m and n by y" where m and n are the nouns immediately to the left and right of the conjunction.

Note that the following might be slightly more efficient:

<lang j> multiplier=: conjunction def '(m * n) * ]'</lang>

Here, the two constants are isolated from the rest of the calculation, so that multiplication is carried out only once, instead of every time the function is used.