a # 1 66 R ' r#def prompt msg;j;k                                             '
a # a,[1]  ' $0 if 0=R,def H j#r#rUQH r#R,Q#msg                               '
a # a,[1]  ' $0 if character def H r#r,(0=R,r)/Fdef                           '
a # a,[1]  'nscreen:$err if ~(~empty k)&&/k#jE'' -.0123456789e''                '
a # a,[1]  ' $0 ifV/def=(def>0)XR,r#Cj                                        '
a # a,[1]  'err:$1 H L#''not exactly '',((V/def>0)/Fdef),'' number'',(V/def>1)/''s'''
a # a,[1]  '" characters may be added or deleted from nscreen                 '
a # a,[1]  ' $0                                                               '
a # a,[1]  '"prompt - prompt and check terminal entry or else default         '
a # a,[1]  '"from ''the apl handbook of techniques'' copyright 1978, ibm.       '
a # a,[1]  '"-prompt can examine keyboard entry, and either accept it         '
a # a,[1]  '" uncritically, return a specified default character vector,      '
a # a,[1]  '" or, if numeric values are requested, will check the             '
a # a,[1]  '" character set used, and can check for the specified length.     '
a # a,[1]  '"-msg is a character string, i.e., the prompting message.         '
a # a,[1]  '"-def, if character, is the default character string, or, ''''      '
a # a,[1]  '"      if a scalar numeric value, n:                              '
a # a,[1]  '"          will accept any numeric vector if n=0                  '
a # a,[1]  '"          will reject vector unless n=Rvector                    '
a # a,[1]  '"      if an integer vector, v, will accept a numeric             '
a # a,[1]  '"          vector if its length is one member of v.               '
a # a,[1]  '"-uses: Gcharacter Gempty Gif GH                                  '
Lfx a