Types
-----

|<a>|    = a task that, when run, produces a value of type 'a

a |->| b = an operation that, when run with a value of type 'a, produces a value
           of type 'b

a |->| b ~ a -> |<b>|

0 |->| a ~ |<a>|


Primitives
----------

task : (a -> b) * a -> |<b>|
task : (0 -> a) -> |<a>|

return : a -> |<a>|

func : (a -> b) -> (a |->| b)

apply : (a |->| b) * a -> |<b>|

suspend : (a -> |<b>|) -> (a |->| b)

ignore : |<b>| -> (a |->| b)

nop : |<'nop'>|

id : a |->| a


return(x) = task(fun() -> x end)
apply(func(f), x) = task(f, x)
suspend(fun(X) -> return(f(x)) end) = func(f)
ignore(x) = suspend(fun(_) -> x)

nop = return('nop')
id = func(fun(X) -> X)

cannot construct an element of type 0 |->| a.


Pipelines
---------

pipe : (a |->| b) * (b |->| c) -> (a |->| c)
pipe : [ a_1 |->| a_2, a_2 |-> a_3, ..., a_n-1 |->| a_n ] -> (a_1 |->| a_n)

bind : |<a>| * (a -> |<b>|) -> |<b>|

feed : |<a>| * (a |->| b) -> |<b>|

sequence : |<a>| * |<b>| -> |< [a, b] >|
sequence : [ |<a_1>|, |<a_2>|, ..., |<a_n>| ] -> |< [a_1, a_2, ..., a_n] >|


pipe(f_1, pipe(f_2, ...f_n...)) = pipe([f_1, f_2, ..., f_n])
pipe(pipe(f, g), h) = pipe(f, pipe(g, h))
pipe(id, f) = f
pipe(f, id) = f

bind(bind(x, f), g) = bind(x, fun(X) -> bind(f X, g) end)
bind(x, return) = x
bind(return(x), f) = f x

feed(x, suspend(f)) = bind(x, f)


Scattering
----------

scatter : |<a>| * |<b>| -> |< [a, b] >|
scatter : [ |<a_1>|, |<a_2>|, ..., |<a_n>| ] -> |< [a_1, a_2, ..., a_n] >|

parallel : (a |->| a') * (b |->| b') -> ([a, b] |-> [a', b'])
parallel : [ a_1 |->| a_1', a_2 |->| a_2', ..., a_n |->| a_n' ]
         -> ([a_1, a_2, ..., a_n] |->| [a_1', a_2', ..., a_n'])

fanout : (a |->| b) * (a |->| c) -> (a |->| [b, c])
fanout : [ a |->| b_1, a |->| b_2, ..., a |->| b_n ]
       -> (a |->| [b_1, b_2, ..., b_n])

pointwise : ([a_1, a_2, ..., a_n] |->| [b_1, b_2, ..., b_n])
	  * ([b_1, b_2, ..., b_n] |->| [c_1, c_2, ..., c_n])
	  -> ([a_1, a_2, ..., a_n] |->| [c_1, c_2, ..., c_n])
pointwise : [ [a_11, a_12, ..., a_1n] |->| [a_21, a_22, ..., a_2n],
	      [a_21, a_22, ..., a_2n] |->| [a_31, a_32, ..., a_3n],
	      ...,
	      [a_m-11, a_m-12, ..., a_m-1n] |->| [a_m1, a_m2, ..., a_mn] ]
	  -> ([a_11, a_12, ..., a_1n] |->| [a_m1, a_m2, ..., a_mn])

map : (a |->| b) * |< [a] >| -> |< [b] >|

reduce : ([a] |->| b) * ([b] |->| b) * |< [a] >| -> |< [c] >|


Choice
------

tag : t * |<a>| -> |< {t, a} >|

tagging : t * (a |->| b) -> (a |->| {t, b})

cases : (a |->| a') * (b |->| b') -> (a+b |->| a'+b')
cases : [ a_1 |->| b_1, a_2 |->| b_2, ..., a_n |->| b_n ]
      -> (a_1+a_2+...+a_n |->| b_1+b_2+...+b_n)

cases nondeterministically picks any non-'nop' output, or is 'nop' if there is
none. use tags to force determinism.

fanin : (a |->| c) * (b |->| c) -> (a+b |->| c)
fanin : [ a_1 |->| b, a_2, |->| b, ..., a_n |->| b ]
      -> (a_1+a_2+...+a_n |->| b)

fanin = cases, since '+' is simple union.

fastest : |<a>| * |<b>| -> |< a+b >|
fastest : [ |<a_1>|, |<a_2>|, ..., |<a_n>| ] -> |< a_1|a_2+...+a_n >|

slowest : |<a>| * |<b>| -> |< a+b >|
slowest : [ |<a_1>|, |<a_2>|, ..., |<a_n>| ] -> |< a_1+a_2+...+a_n >|


Loops
-----

loopback : (a |->| {'stop', b}+{'loop', a}) -> (a |->| b)

loopback terminates when the operation returns 'stop'.