Lazy brainfuck programmer
Jelly, 18 bytes
V©_¥®N,$Ø&lt;xµ¹e?ØD)

A full program. Assumes (like everyone else has) that no actual Brainfuck evaluation has to be made (no balancing of unbalanced brackets)
Try it online!
How?
V©_¥®N,$Ø&lt;xµ¹e?ØD) - Main Link: list of characters, s
                 ) - for each character, c, in s:
               ØD  -   digits = &quot;0123456789&quot;
              ?    -   if...
             e     -   ...condition: (c) exists in? (digits)
           µ       -   ...then: monadic link:
    ®              -            recall from register (initially 0) 
   ¥               -            last two links as a dyad i.e. f(c, ®):
V                  -              evaluate (c)
 ©                 -              (copy to the register)
  _                -              subtract (®)  i.e. x = value(c) - register
       $           -            last two links as a monad i.e. f(x):
     N             -              negate (x)
      ,            -              pair with (x)  -&gt; [-x,x]
        Ø&lt;         -            list of characters = &quot;&lt;&gt;&quot;
          x        -            repeat (vectorises) - negatives act like 0
            ¹      -   ...else: identity - i.e. f(c) -&gt; c
                   - implicit (smashing) print