Smalltalk does have precedence, just not among infix operators. It has keyword, infix, and postfix expressions and needs to specify the relative precedence between those. In other words, the language has to decide if:

   a b: c - d e

Is parsed like:

   a b: (c - (d e))
   a b: ((c - d) e)
   (a b: c) - (d e)
   (a b: (c - d)) e
   ((a b: c) - d) e