The semantics of this language I'm thinking of are essentially scheme, with layout as opposed to bracket syntax, or more precisely being able to use either. The parallel blocks initially will be implemented using engines. The syncronicity issues can be implemented in a similar fasion, with a proxy function, to mediate between the function proper and it's return value.

delay s m =
:init
list/fill buffer s m
result = first buffer
buffer = tail buffer ++ s
result
delay-line signal =
signal + delay signal m
synth f e =
:init
s = 0
s = osc (f + e * delay m s)