Implementation of Forth "NUMBER"
Features:
  o Default base is 10
  o Arbitrary base specifiable like so:  16:deadbeef
  o Case insensitive up through base 36, then case insensitive
  o Handles integers and floating point numbers
  o Base 16 shortcut: x:deadbeef
  o Binary shortcut: b:0010011


:: 0-9?  48 - 10 .U< 0=; ;;
:: A-Z?  17 - 27 .U< 0=; 10 + ;;
:: _a-z?  32 - 27 .U< 0=; 36 + ;;
:: !0  .C@ 0= 1 ?ERR ;
:: e?  .C@ 101 = 0=; 1+ !0 1 R2+! ;;
:: :?  .C@ 58 = 0=; 1+ >R NIP 0 R> !0 ;
:: :!  .C@++ 58 <> 2 ?ERR 0 SWAP !0 ;
:: -?  .C@ 45 = IF 1+ !0 -1 ;, THEN 1 ;
:: a->a?  OVER 37 < 0=; 35 .> 0=; 26 - ;
:: <BASE?  a->A? OVER .U>= 3 ?ERR
:: DIGIT  .C@++ 0-9? A-Z? _a-z? 4 ERR [[
:: FOLD  OVER >R ROT R! -ROT DIGIT R> SWAP <BASE? SWAP R> * + ROT DROP SWAP ;
:: POST  0? FOLD ME ;
:: .POST  e? 0? FOLD ME ;
:: WRAP  POST DROP NIP * ;
:: ILIT?  STATE @ 0=; TAIL? OFF ILIT ;
:: FLIT?  STATE @ 0=; TAIL? OFF FLIT ;
:: FMT  SWAP S>F 1.0E1 F** S>F F* ;
:: OUT  SWAP ROT DROP ROT * FMT FLIT? 5 n;
:: EXP  >R -? 10 ROT 0 SWAP WRAP R> - OUT ;
:: .?  .C@ 46 = 0=; 1+ R! .POST DUP R> - EXP ;
:: !.  OVER C@ 46 = 5 ?ERR ;
:: PRE  :? .? 0? FOLD ME ;
:: BASE?  >R OVER C@ = 0=;; NIP 1+ R> SWAP :! ;
:: BASE  120 16 BASE? 98 2 BASE? 0 SWAP PRE ;
: CSTR  .C@++ OVER + 0 SWAP C! ;
: NUMBER  CSTR !0 -? !. 10 ROT BASE WRAP ILIT? ;