[fexl]

If you're interested in dabbling a bit, here's the grammar I'm using:

Here is the basic Fexl language, which can express all computable functions.

   expr = \atom expr
   expr = factor
   expr = factor expr

   factor = atom
   factor = (expr)

 The full language includes two additional notations for convenience.

   expr = \atom=factor expr
        = (\atom expr) factor

   expr = factor; expr
        = factor (expr)