Reducers

A reducer is Signum's single callable form. It takes one argument (by convention called a) and returns one value.

@ double : a
    ((a * 2) >> se_ok) ->
..

(5 >> double) >> print   ~~ prints 10

Compose by piping

@ shout : a
    ((a + "!") >> se_ok) ->
..

("hi" >> shout >> shout) >> print   ~~ prints hi!!

Reducers are pure: same input, same output, every backend, every machine. There are no hidden globals and no I/O side effects inside a reducer unless it explicitly pipes into an io.* builtin.

Shapes

The argument a is usually a dict, which lets a reducer accept named fields and ignore the rest:

@ classify : a
    n ~ a["n"]
    ? (n = 0) ("zero" >> se_ok) -> ..
    ("nonzero" >> se_ok) ->
..

{"n": 0, "note": "ignored"} >> classify >> print