Interactive parser

Just to play with `parse_something`

~~~
$ test_parser -i -n
--> hello world
Got ABlockExpr
--> "hello world" 
Got AStringExpr
--> for x in [1,2,3] do
... print x
... end
Got ABlockExpr
--> fun foo do
... print "hello"
... end
Got AModule
--> for x in in in p
        for x in in in p
                 ^: Syntax error: unexpected keyword 'in'.
--> :q
~~~