Surprise, Macsyma, which is written in Lisp has that syntax. Macsyma is the earlier computer algebra system, which Kent Pitman mentioned in that post. He also mentions that Wolfram knew Macsyma.

Example:

    applysymmetry(exp,opdum,symtype):=block(
      [getdum:get(opdum,symtype),piece,inflag:true,partswitch:true],
      if getdum=false then return(exp),
      subst(lambda([[arglist]],
                   apply('aplsym1,append(getdum,[arglist,opdum]))),
            opdum,exp))$

If you know Lisp, you will recognize typical constructs like IF, RETURN, SUBST, LAMBDA, APPLY, APPEND, ...