Function substring_search 

pub fn substring_search(
    haystack: &str,
    needle: &str,
    matches: &str,
    haystack_len: u32,
    needle_len: u32,
) -> Program

Build a Program that writes 1 to matches[i] when haystack[i..] starts with needle, else 0. Both buffers are u32 byte arrays packed one byte per u32 for simplicity (a future packed-u8 version is Category A over DataType::U8).