As below, lambda literal with do..end block can raise syntax error.
$ ./ruby -ve 'p ->() do a(1) do end end'
ruby 2.3.0dev (2015-04-26 trunk 50395) [x86_64-darwin14]
-e:1: syntax error, unexpected keyword_do_block, expecting keyword_end
p ->() do a(1) do end end
^