On 2 January 2011 13:35, Stephen Tetley
Hello all
Can a lazy cons be implemented for (infinite) Streams in the Stream-Fusion style?
In the standard stream fusion style, all stream operations are strict in the stream itself (that is, the pair of stepper function and initial state, not strict in the unfolded sequence or elements). Thus it is not possible to write things like:
bad_ones :: Stream Int bad_ones = s where s = 1 `S.cons` s
I'm not sure if making the stream operations lazy in the stream argument (e.g. using an irrefutable ~pattern) would interfere with the usual stream optimisations. It's an interesting question. The usual optimisations rely on having access to the definitions of input streams and will not apply to a circular definition such as the above. This strictness issue isn't a semantic problem problem when applying stream fusion to data structures like lists. A circular definition of a list will simply not fuse (there is nowhere to apply the stream/unstream rule). Duncan