divert(-1)
An experiment in defining macro options as key=val;key= ...
                                `resistor( linespec,
                                           cycles=n;type=E|Q|H;side=L|R)
                                 chars : E=ebox
                                         Q=offset
                                         H=squared (default 3 cycles)
                                         R=to right of drawing direction'
define(`sc_readkey',
 `pushdef(`m4xt',index(`$1',`$2'=))ifelse(m4xt,-1,
   `pushdef(`m4'$2,`$3')',
   `define(`m4tmp',substr(`$1',eval(m4xt+len(`$2')+1)))dnl
    ifelse(index(m4tmp,;),-1,
     `pushdef(`m4'$2,m4tmp)',
     `pushdef(`m4'$2,substr(m4tmp,0,index(m4tmp,;)))')')dnl
  popdef(`m4xt')')
define(`xesistor',
 `sc_readkey(`$2',cycles,4)dnl
  sc_readkey(`$2',type,N)dnl
  sc_readkey(`$2',side,R)dnl
  popdef(`m4cycles')dnl
  popdef(`m4type')dnl
  popdef(`m4side')dnl
')
divert(0)dnl
% Test.m4
.PS
  xesistor(,type=E;cycles=5;)
  cycles:m4cycles
  type:m4type
  side:m4side
.PE