samer@3: function [h,x]=span(f,x)
samer@3: % span - divide sequence using a test function
samer@3: %
samer@3: % span :: (A->bool), seq(A) -> seq(A), seq(A).
samer@3: %
samer@3: % span(f,x) = takeWhile(f,x), dropWhile(f,x)
samer@3: % Will not terminate if head segments turns out to be infinite.
samer@3: [Y,x]=spanc(f,x);
samer@3: h=cellseq(Y);