impls/factor/step2_eval/step2_eval.factor

   1 ! Copyright (C) 2015 Jordan Lewis.
   2 ! See http://factorcode.org/license.txt for BSD license.
   3 USING: accessors arrays assocs combinators combinators.short-circuit
   4 continuations fry io kernel math lib.printer lib.reader lib.types
   5 quotations readline sequences ;
   6 IN: step2_eval
   7
   8 CONSTANT: repl-env H{
   9     { "+" [ + ] }
  10     { "-" [ - ] }
  11     { "*" [ * ] }
  12     { "/" [ / ] }
  13 }
  14
  15 DEFER: EVAL
  16
  17 : eval-symbol ( sym env -- ast )
  18     [ name>> ] dip ?at [ "no variable " prepend throw ] unless ;
  19
  20 : eval-list ( list env -- ast )
  21     '[ _ EVAL ] map ;
  22
  23 : eval-assoc ( assoc env -- ast )
  24     '[ [ _ EVAL ] bi@ ] assoc-map ;
  25
  26 : eval-ast ( ast env -- ast )
  27     {
  28         { [ over malsymbol? ] [ eval-symbol ] }
  29         { [ over sequence? ]  [ eval-list ] }
  30         { [ over assoc? ]     [ eval-assoc ] }
  31         [ drop ]
  32     } cond ;
  33
  34 : READ ( str -- maltype ) read-str ;
  35
  36 : EVAL ( maltype env -- maltype )
  37     eval-ast dup { [ array? ] [ empty? not ] } 1&& [
  38         unclip
  39         dup quotation? [ "not a fn" throw ] unless
  40         with-datastack first
  41     ] when ;
  42
  43 : PRINT ( maltype -- str ) pr-str ;
  44
  45 : REP ( str -- str )
  46     [
  47         READ repl-env EVAL PRINT
  48     ] [
  49         nip pr-str "Error: " swap append
  50     ] recover ;
  51
  52 : REPL ( -- )
  53     [
  54         "user> " readline [
  55             [ REP print flush ] unless-empty
  56         ] keep
  57     ] loop ;
  58
  59 MAIN: REPL