In Haskell 'do { e1; e2 }' expands to 'bind e1 (\_ -> e2) ' and does not fix
"return type" of 'e1'. This is usable, for example, with parser combinators,
where we often need call parser and discards its value. Another example --- IO
action, which returns some non-interesting technical details (as num of
inserted rows or elapsed time).
In Ur, one need noisy 'ignore e1; e2' or (with unused free in 'e2' variable)
'_i <- e1; e2' if type 'e1' is not 'm {}'. Does this really help to prevent
errors? Which kinds? I am sure, the cost is too large.
At least, this difference should be documented in the reference manual: I have
thought that improperly declared monad for a some time.
PS. And also fix typo in chapter 4.1, Lexical conventions, of manual.pdf: in
the second row of table ASCII representation of long arrow should be '-->' but
is '->'
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