A little of coordination for Rosettacode

[bearophile]

> so when you print the tape you trim the blanks away at both 
> ends.

A wrong trimming code:


string toString() const {
     // Blank-stripped tape.
     const t2 = tape
                .find!(c => c != blank)()
                .retro()
                .find!(c => c != blank)()
                .retro();

     return format("...%(%)...", t2.empty ? [blank] : t2)
            ~ '\n'
            ~ format("%" ~ text(position + 4) ~ "s", "^")
            ~ '\n';
}


It gives:

Busy beaver machine (3-state, 2-symbol):
...0...
    ^
...1...
     ^


The second line should show the cell up to the head position:

Busy beaver machine (3-state, 2-symbol):
...0...
    ^
...10...
     ^


There are many ways to improve this program, like trimming away 
the blanks correctly, but I think the code is acceptable now:

http://rosettacode.org/wiki/Universal_Turing_machine#D

Bye,
bearophile