impls/basic/stepA_mal.in.bas

   1 GOTO MAIN
   2
   3 REM $INCLUDE: 'mem.in.bas'
   4 REM $INCLUDE: 'types.in.bas'
   5 REM $INCLUDE: 'readline.in.bas'
   6 REM $INCLUDE: 'reader.in.bas'
   7 REM $INCLUDE: 'printer.in.bas'
   8 REM $INCLUDE: 'env.in.bas'
   9 REM $INCLUDE: 'core.in.bas'
  10
  11 REM $INCLUDE: 'debug.in.bas'
  12
  13 REM READ is inlined in RE
  14
  15 REM QUASIQUOTE(A) -> R
  16 SUB QUASIQUOTE
  17   REM pair?
  18   GOSUB TYPE_A
  19   IF T<6 OR T>7 THEN GOTO QQ_QUOTE
  20   IF (Z%(A+1)=0) THEN GOTO QQ_QUOTE
  21   GOTO QQ_UNQUOTE
  22
  23   QQ_QUOTE:
  24     REM ['quote, ast]
  25     B$="quote":T=5:GOSUB STRING
  26     B=R:A=A:GOSUB LIST2
  27     AY=B:GOSUB RELEASE
  28
  29     GOTO QQ_DONE
  30
  31   QQ_UNQUOTE:
  32     R=Z%(A+2)
  33     IF (Z%(R)AND 31)<>5 THEN GOTO QQ_SPLICE_UNQUOTE
  34     IF S$(Z%(R+1))<>"unquote" THEN GOTO QQ_SPLICE_UNQUOTE
  35       REM [ast[1]]
  36       R=Z%(Z%(A+1)+2)
  37       GOSUB INC_REF_R
  38
  39       GOTO QQ_DONE
  40
  41   QQ_SPLICE_UNQUOTE:
  42     GOSUB PUSH_A
  43     REM rest of cases call quasiquote on ast[1..]
  44     A=Z%(A+1):CALL QUASIQUOTE
  45     W=R
  46     GOSUB POP_A
  47
  48     REM set A to ast[0] for last two cases
  49     A=Z%(A+2)
  50
  51     REM pair?
  52     GOSUB TYPE_A
  53     IF T<6 OR T>7 THEN GOTO QQ_DEFAULT
  54     IF (Z%(A+1)=0) THEN GOTO QQ_DEFAULT
  55
  56     B=Z%(A+2)
  57     IF (Z%(B)AND 31)<>5 THEN GOTO QQ_DEFAULT
  58     IF S$(Z%(B+1))<>"splice-unquote" THEN QQ_DEFAULT
  59       REM ['concat, ast[0][1], quasiquote(ast[1..])]
  60
  61       B=Z%(Z%(A+1)+2)
  62       B$="concat":T=5:GOSUB STRING:C=R
  63       A=W:GOSUB LIST3
  64       REM release inner quasiquoted since outer list takes ownership
  65       AY=A:GOSUB RELEASE
  66       AY=C:GOSUB RELEASE
  67       GOTO QQ_DONE
  68
  69   QQ_DEFAULT:
  70     REM ['cons, quasiquote(ast[0]), quasiquote(ast[1..])]
  71
  72     Q=W:GOSUB PUSH_Q
  73     REM A set above to ast[0]
  74     CALL QUASIQUOTE
  75     B=R
  76     GOSUB POP_Q:W=Q
  77
  78     B$="cons":T=5:GOSUB STRING:C=R
  79     A=W:GOSUB LIST3
  80     REM release inner quasiquoted since outer list takes ownership
  81     AY=A:GOSUB RELEASE
  82     AY=B:GOSUB RELEASE
  83     AY=C:GOSUB RELEASE
  84   QQ_DONE:
  85 END SUB
  86
  87 REM MACROEXPAND(A, E) -> A:
  88 SUB MACROEXPAND
  89   GOSUB PUSH_A
  90
  91   MACROEXPAND_LOOP:
  92     REM list?
  93     GOSUB TYPE_A
  94     IF T<>6 THEN GOTO MACROEXPAND_DONE
  95     REM non-empty?
  96     IF Z%(A+1)=0 THEN GOTO MACROEXPAND_DONE
  97     B=Z%(A+2)
  98     REM symbol? in first position
  99     IF (Z%(B)AND 31)<>5 THEN GOTO MACROEXPAND_DONE
 100     REM defined in environment?
 101     K=B:CALL ENV_FIND
 102     IF R=-1 THEN GOTO MACROEXPAND_DONE
 103     B=R4
 104     REM macro?
 105     IF (Z%(B)AND 31)<>11 THEN GOTO MACROEXPAND_DONE
 106
 107     F=B:AR=Z%(A+1):CALL APPLY
 108     A=R
 109
 110     GOSUB PEEK_Q:AY=Q
 111     REM if previous A was not the first A into macroexpand (i.e. an
 112     REM intermediate form) then free it
 113     IF A<>AY THEN GOSUB PEND_A_LV
 114
 115     IF ER<>-2 THEN GOTO MACROEXPAND_DONE
 116     GOTO MACROEXPAND_LOOP
 117
 118   MACROEXPAND_DONE:
 119     GOSUB POP_Q: REM pop original A
 120 END SUB
 121
 122 REM EVAL_AST(A, E) -> R
 123 SUB EVAL_AST
 124   REM push A and E on the stack
 125   Q=E:GOSUB PUSH_Q
 126   GOSUB PUSH_A
 127
 128   IF ER<>-2 THEN GOTO EVAL_AST_RETURN
 129
 130   GOSUB TYPE_A
 131   IF T=5 THEN GOTO EVAL_AST_SYMBOL
 132   IF T>5 AND T<9 THEN GOTO EVAL_AST_SEQ
 133
 134   REM scalar: deref to actual value and inc ref cnt
 135   R=A
 136   GOSUB INC_REF_R
 137   GOTO EVAL_AST_RETURN
 138
 139   EVAL_AST_SYMBOL:
 140     K=A:GOTO ENV_GET
 141     ENV_GET_RETURN:
 142     GOTO EVAL_AST_RETURN
 143
 144   EVAL_AST_SEQ:
 145     REM setup the stack for the loop
 146     GOSUB MAP_LOOP_START
 147
 148     EVAL_AST_SEQ_LOOP:
 149       REM check if we are done evaluating the source sequence
 150       IF Z%(A+1)=0 THEN GOTO EVAL_AST_SEQ_LOOP_DONE
 151
 152       REM if we are returning to DO, then skip last element
 153       REM The EVAL_DO call to EVAL_AST must be call #2 for EVAL_AST to
 154       REM return early and for TCO to work
 155       Q=5:GOSUB PEEK_Q_Q
 156       IF Q=2 AND Z%(Z%(A+1)+1)=0 THEN GOTO EVAL_AST_SEQ_LOOP_DONE
 157
 158       REM call EVAL for each entry
 159       GOSUB PUSH_A
 160       IF T<>8 THEN A=Z%(A+2)
 161       IF T=8 THEN A=Z%(A+3)
 162       Q=T:GOSUB PUSH_Q: REM push/save type
 163       CALL EVAL
 164       GOSUB POP_Q:T=Q: REM pop/restore type
 165       GOSUB POP_A
 166       M=R
 167
 168       REM if error, release the unattached element
 169       REM TODO: is R=0 correct?
 170       IF ER<>-2 THEN AY=R:GOSUB RELEASE:R=0:GOTO EVAL_AST_SEQ_LOOP_DONE
 171
 172       REM for hash-maps, copy the key (inc ref since we are going to
 173       REM release it below)
 174       IF T=8 THEN N=M:M=Z%(A+2):Z%(M)=Z%(M)+32
 175
 176
 177       REM update the return sequence structure
 178       REM release N (and M if T=8) since seq takes full ownership
 179       C=1:GOSUB MAP_LOOP_UPDATE
 180
 181       REM process the next sequence entry from source list
 182       A=Z%(A+1)
 183
 184       GOTO EVAL_AST_SEQ_LOOP
 185     EVAL_AST_SEQ_LOOP_DONE:
 186       REM cleanup stack and get return value
 187       GOSUB MAP_LOOP_DONE
 188       GOTO EVAL_AST_RETURN
 189
 190   EVAL_AST_RETURN:
 191     REM pop A and E off the stack
 192     GOSUB POP_A
 193     GOSUB POP_Q:E=Q
 194 END SUB
 195
 196 REM EVAL(A, E) -> R
 197 SUB EVAL
 198   LV=LV+1: REM track basic return stack level
 199
 200   REM push A and E on the stack
 201   Q=E:GOSUB PUSH_Q
 202   GOSUB PUSH_A
 203
 204   REM PRINT "EVAL A:"+STR$(A)+",X:"+STR$(X)+",LV:"+STR$(LV)+",FRE:"+STR$(FRE(0))
 205
 206   EVAL_TCO_RECUR:
 207
 208   IF ER<>-2 THEN GOTO EVAL_RETURN
 209
 210   REM AZ=A:B=1:GOSUB PR_STR
 211   REM PRINT "EVAL: "+R$+" [A:"+STR$(A)+", LV:"+STR$(LV)+"]"
 212
 213   GOSUB LIST_Q
 214   IF R THEN GOTO APPLY_LIST
 215   EVAL_NOT_LIST:
 216   REM ELSE
 217     CALL EVAL_AST
 218     GOTO EVAL_RETURN
 219
 220   APPLY_LIST:
 221     CALL MACROEXPAND
 222
 223     GOSUB LIST_Q
 224     IF R<>1 THEN GOTO EVAL_NOT_LIST
 225
 226     GOSUB EMPTY_Q
 227     IF R THEN R=A:GOSUB INC_REF_R:GOTO EVAL_RETURN
 228
 229     A0=Z%(A+2)
 230
 231     REM get symbol in A$
 232     IF (Z%(A0)AND 31)<>5 THEN A$=""
 233     IF (Z%(A0)AND 31)=5 THEN A$=S$(Z%(A0+1))
 234
 235     IF A$="def!" THEN GOTO EVAL_DEF
 236     IF A$="let*" THEN GOTO EVAL_LET
 237     IF A$="quote" THEN GOTO EVAL_QUOTE
 238     IF A$="quasiquote" THEN GOTO EVAL_QUASIQUOTE
 239     IF A$="defmacro!" THEN GOTO EVAL_DEFMACRO
 240     IF A$="macroexpand" THEN GOTO EVAL_MACROEXPAND
 241     IF A$="try*" THEN GOTO EVAL_TRY
 242     IF A$="do" THEN GOTO EVAL_DO
 243     IF A$="if" THEN GOTO EVAL_IF
 244     IF A$="fn*" THEN GOTO EVAL_FN
 245     GOTO EVAL_INVOKE
 246
 247     EVAL_GET_A3:
 248       A3=Z%(Z%(Z%(Z%(A+1)+1)+1)+2)
 249     EVAL_GET_A2:
 250       A2=Z%(Z%(Z%(A+1)+1)+2)
 251     EVAL_GET_A1:
 252       A1=Z%(Z%(A+1)+2)
 253       RETURN
 254
 255     EVAL_DEF:
 256       REM PRINT "def!"
 257       GOSUB EVAL_GET_A2: REM set A1 and A2
 258
 259       Q=A1:GOSUB PUSH_Q
 260       A=A2:CALL EVAL: REM eval a2
 261       GOSUB POP_Q:A1=Q
 262
 263       IF ER<>-2 THEN GOTO EVAL_RETURN
 264
 265       REM set a1 in env to a2
 266       K=A1:C=R:GOSUB ENV_SET
 267       GOTO EVAL_RETURN
 268
 269     EVAL_LET:
 270       REM PRINT "let*"
 271       GOSUB EVAL_GET_A2: REM set A1 and A2
 272
 273       Q=A2:GOSUB PUSH_Q: REM push/save A2
 274       Q=E:GOSUB PUSH_Q: REM push env for for later release
 275
 276       REM create new environment with outer as current environment
 277       C=E:GOSUB ENV_NEW
 278       E=R
 279       EVAL_LET_LOOP:
 280         IF Z%(A1+1)=0 THEN GOTO EVAL_LET_LOOP_DONE
 281
 282         Q=A1:GOSUB PUSH_Q: REM push A1
 283         REM eval current A1 odd element
 284         A=Z%(Z%(A1+1)+2):CALL EVAL
 285         GOSUB POP_Q:A1=Q: REM pop A1
 286
 287         IF ER<>-2 THEN GOTO EVAL_LET_LOOP_DONE
 288
 289         REM set key/value in the environment
 290         K=Z%(A1+2):C=R:GOSUB ENV_SET
 291         AY=R:GOSUB RELEASE: REM release our use, ENV_SET took ownership
 292
 293         REM skip to the next pair of A1 elements
 294         A1=Z%(Z%(A1+1)+1)
 295         GOTO EVAL_LET_LOOP
 296
 297       EVAL_LET_LOOP_DONE:
 298         GOSUB POP_Q:AY=Q: REM pop previous env
 299
 300         REM release previous environment if not the current EVAL env
 301         GOSUB PEEK_Q_2
 302         IF AY<>Q THEN GOSUB RELEASE
 303
 304         GOSUB POP_Q:A2=Q: REM pop A2
 305         A=A2:GOTO EVAL_TCO_RECUR: REM TCO loop
 306
 307     EVAL_DO:
 308       A=Z%(A+1): REM rest
 309       GOSUB PUSH_A: REM push/save A
 310
 311       REM this must be EVAL_AST call #2 for EVAL_AST to return early
 312       REM and for TCO to work
 313       CALL EVAL_AST
 314
 315       REM cleanup
 316       AY=R: REM get eval'd list for release
 317
 318       GOSUB POP_A: REM pop/restore original A for LAST
 319       GOSUB LAST: REM get last element for return
 320       A=R: REM new recur AST
 321
 322       REM cleanup
 323       GOSUB RELEASE: REM release eval'd list
 324       AY=A:GOSUB RELEASE: REM release LAST value (not sure why)
 325
 326       GOTO EVAL_TCO_RECUR: REM TCO loop
 327
 328     EVAL_QUOTE:
 329       R=Z%(Z%(A+1)+2)
 330       GOSUB INC_REF_R
 331       GOTO EVAL_RETURN
 332
 333     EVAL_QUASIQUOTE:
 334       R=Z%(Z%(A+1)+2)
 335       A=R:CALL QUASIQUOTE
 336       A=R
 337       REM add quasiquote result to pending release queue to free when
 338       REM next lower EVAL level returns (LV)
 339       GOSUB PEND_A_LV
 340
 341       GOTO EVAL_TCO_RECUR: REM TCO loop
 342
 343     EVAL_DEFMACRO:
 344       REM PRINT "defmacro!"
 345       GOSUB EVAL_GET_A2: REM set A1 and A2
 346
 347       Q=A1:GOSUB PUSH_Q: REM push A1
 348       A=A2:CALL EVAL: REM eval A2
 349       GOSUB POP_Q:A1=Q: REM pop A1
 350
 351       REM change function to macro
 352       Z%(R)=Z%(R)+1
 353
 354       REM set A1 in env to A2
 355       K=A1:C=R:GOSUB ENV_SET
 356       GOTO EVAL_RETURN
 357
 358     EVAL_MACROEXPAND:
 359       REM PRINT "macroexpand"
 360       R=Z%(Z%(A+1)+2)
 361       A=R:CALL MACROEXPAND
 362       R=A
 363
 364       REM since we are returning it unevaluated, inc the ref cnt
 365       GOSUB INC_REF_R
 366       GOTO EVAL_RETURN
 367
 368     EVAL_TRY:
 369       REM PRINT "try*"
 370       GOSUB EVAL_GET_A1: REM set A1
 371
 372       GOSUB PUSH_A: REM push/save A
 373       A=A1:CALL EVAL: REM eval A1
 374       GOSUB POP_A: REM pop/restore A
 375
 376       GOSUB EVAL_GET_A2: REM set A1 and A2
 377
 378       REM if there is no error or catch block then return
 379       IF ER=-2 OR A2=0 THEN GOTO EVAL_RETURN
 380
 381       REM create environment for the catch block eval
 382       C=E:GOSUB ENV_NEW:E=R
 383
 384       A=A2:GOSUB EVAL_GET_A2: REM set A1 and A2 from catch block
 385
 386       REM create object for ER=-1 type raw string errors
 387       IF ER=-1 THEN B$=E$:T=4:GOSUB STRING:ER=R:GOSUB INC_REF_R
 388
 389       REM bind the catch symbol to the error object
 390       K=A1:C=ER:GOSUB ENV_SET
 391       AY=R:GOSUB RELEASE: REM release our use, env took ownership
 392
 393       REM unset error for catch eval
 394       ER=-2:E$=""
 395
 396       A=A2:CALL EVAL
 397
 398       GOTO EVAL_RETURN
 399
 400     EVAL_IF:
 401       GOSUB EVAL_GET_A1: REM set A1
 402       GOSUB PUSH_A: REM push/save A
 403       A=A1:CALL EVAL
 404       GOSUB POP_A: REM pop/restore A
 405       IF (R=0) OR (R=2) THEN GOTO EVAL_IF_FALSE
 406
 407       EVAL_IF_TRUE:
 408         AY=R:GOSUB RELEASE
 409         GOSUB EVAL_GET_A2: REM set A1 and A2 after EVAL
 410         A=A2:GOTO EVAL_TCO_RECUR: REM TCO loop
 411       EVAL_IF_FALSE:
 412         AY=R:GOSUB RELEASE
 413         REM if no false case (A3), return nil
 414         GOSUB COUNT
 415         IF R<4 THEN R=0:GOSUB INC_REF_R:GOTO EVAL_RETURN
 416         GOSUB EVAL_GET_A3: REM set A1 - A3 after EVAL
 417         A=A3:GOTO EVAL_TCO_RECUR: REM TCO loop
 418
 419     EVAL_FN:
 420       GOSUB EVAL_GET_A2: REM set A1 and A2
 421       T=10:L=A2:M=A1:N=E:GOSUB ALLOC: REM mal function
 422       GOTO EVAL_RETURN
 423
 424     EVAL_INVOKE:
 425       CALL EVAL_AST
 426
 427       REM if error, return f/args for release by caller
 428       IF ER<>-2 THEN GOTO EVAL_RETURN
 429
 430       REM push f/args for release after call
 431       GOSUB PUSH_R
 432
 433       AR=Z%(R+1): REM rest
 434       F=Z%(R+2)
 435
 436       REM if metadata, get the actual object
 437       GOSUB TYPE_F
 438       IF T=14 THEN F=Z%(F+1):GOSUB TYPE_F
 439
 440       ON T-8 GOTO EVAL_DO_FUNCTION,EVAL_DO_MAL_FUNCTION,EVAL_DO_MAL_FUNCTION
 441
 442       REM if error, pop and return f/args for release by caller
 443       GOSUB POP_R
 444       ER=-1:E$="apply of non-function":GOTO EVAL_RETURN
 445
 446       EVAL_DO_FUNCTION:
 447         REM regular function
 448         IF Z%(F+1)<60 THEN GOSUB DO_FUNCTION:GOTO EVAL_DO_FUNCTION_SKIP
 449         REM for recur functions (apply, map, swap!), use GOTO
 450         IF Z%(F+1)>60 THEN CALL DO_TCO_FUNCTION
 451         EVAL_DO_FUNCTION_SKIP:
 452
 453         REM pop and release f/args
 454         GOSUB POP_Q:AY=Q
 455         GOSUB RELEASE
 456         GOTO EVAL_RETURN
 457
 458       EVAL_DO_MAL_FUNCTION:
 459         Q=E:GOSUB PUSH_Q: REM save the current environment for release
 460
 461         REM create new environ using env and params stored in function
 462         C=Z%(F+3):A=Z%(F+2):B=AR:GOSUB ENV_NEW_BINDS
 463
 464         REM release previous env if it is not the top one on the
 465         REM stack (X%(X-2)) because our new env refers to it and
 466         REM we no longer need to track it (since we are TCO recurring)
 467         GOSUB POP_Q:AY=Q
 468         GOSUB PEEK_Q_2
 469         IF AY<>Q THEN GOSUB RELEASE
 470
 471         REM claim the AST before releasing the list containing it
 472         A=Z%(F+1):Z%(A)=Z%(A)+32
 473         REM add AST to pending release queue to free as soon as EVAL
 474         REM actually returns (LV+1)
 475         LV=LV+1:GOSUB PEND_A_LV:LV=LV-1
 476
 477         REM pop and release f/args
 478         GOSUB POP_Q:AY=Q
 479         GOSUB RELEASE
 480
 481         REM A set above
 482         E=R:GOTO EVAL_TCO_RECUR: REM TCO loop
 483
 484   EVAL_RETURN:
 485     REM AZ=R: B=1: GOSUB PR_STR
 486     REM PRINT "EVAL_RETURN R: ["+R$+"] ("+STR$(R)+"), LV:"+STR$(LV)+",ER:"+STR$(ER)
 487
 488     REM release environment if not the top one on the stack
 489     GOSUB PEEK_Q_1
 490     IF E<>Q THEN AY=E:GOSUB RELEASE
 491
 492     LV=LV-1: REM track basic return stack level
 493
 494     REM release everything we couldn't release earlier
 495     GOSUB RELEASE_PEND
 496
 497     REM trigger GC
 498     #cbm T=FRE(0)
 499     #qbasic T=0
 500
 501     REM pop A and E off the stack
 502     GOSUB POP_A
 503     GOSUB POP_Q:E=Q
 504
 505 END SUB
 506
 507 REM PRINT is inlined in REP
 508
 509
 510 REM RE(A$) -> R
 511 REM Assume D has repl_env
 512 REM caller must release result
 513 RE:
 514   R1=-1
 515   GOSUB READ_STR: REM inlined MAL_READ
 516   R1=R
 517   IF ER<>-2 THEN GOTO RE_DONE
 518
 519   A=R:E=D:CALL EVAL
 520
 521   RE_DONE:
 522     REM Release memory from MAL_READ
 523     AY=R1:GOSUB RELEASE
 524     RETURN: REM caller must release result of EVAL
 525
 526 REM REP(A$) -> R$
 527 REM Assume D has repl_env
 528 SUB REP
 529   R2=-1
 530
 531   GOSUB RE
 532   R2=R
 533   IF ER<>-2 THEN GOTO REP_DONE
 534
 535   AZ=R:B=1:GOSUB PR_STR: REM MAL_PRINT
 536
 537   REP_DONE:
 538     REM Release memory from MAL_READ and EVAL
 539     AY=R2:GOSUB RELEASE
 540 END SUB
 541
 542 REM MAIN program
 543 MAIN:
 544   GOSUB INIT_MEMORY
 545
 546   LV=0
 547
 548   REM create repl_env
 549   C=0:GOSUB ENV_NEW:D=R
 550
 551   REM core.EXT: defined in Basic
 552   E=D:GOSUB INIT_CORE_NS: REM set core functions in repl_env
 553
 554   ZT=ZI: REM top of memory after base repl_env
 555
 556   REM core.mal: defined using the language itself
 557   #cbm A$="(def! *host-language* "+CHR$(34)+"C64 BASIC"+CHR$(34)+")"
 558   #qbasic A$="(def! *host-language* "+CHR$(34)+"QBasic"+CHR$(34)+")"
 559   GOSUB RE:AY=R:GOSUB RELEASE
 560
 561   A$="(def! not (fn* (a) (if a false true)))"
 562   GOSUB RE:AY=R:GOSUB RELEASE
 563
 564   A$="(def! load-file (fn* (f) (do (eval (read-file f)) nil)))"
 565   GOSUB RE:AY=R:GOSUB RELEASE
 566
 567   A$="(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs)"
 568   A$=A$+" (if (> (count xs) 1) (nth xs 1) (throw "+CHR$(34)+"odd number of"
 569   A$=A$+" forms to cond"+CHR$(34)+")) (cons 'cond (rest (rest xs)))))))"
 570   GOSUB RE:AY=R:GOSUB RELEASE
 571
 572   REM load the args file
 573   A$="(load-file "+CHR$(34)+".args.mal"+CHR$(34)+")"
 574   GOSUB RE:AY=R:GOSUB RELEASE
 575
 576   IF ER>-2 THEN GOSUB PRINT_ERROR:END
 577
 578   REM set the argument list
 579   A$="(def! *ARGV* (rest -*ARGS*-))"
 580   GOSUB RE:AY=R:GOSUB RELEASE
 581
 582   REM get the first argument
 583   A$="(first -*ARGS*-)"
 584   GOSUB RE
 585
 586   REM no arguments, start REPL loop
 587   IF R<16 THEN GOTO REPL
 588
 589   REM if there is an argument, then run it as a program
 590
 591   RUN_PROG:
 592     REM free up first arg because we get it again
 593     AY=R:GOSUB RELEASE
 594     REM run a single mal program and exit
 595     A$="(load-file (first -*ARGS*-))"
 596     GOSUB RE
 597     IF ER<>-2 THEN GOSUB PRINT_ERROR
 598     GOTO QUIT
 599
 600   REPL:
 601     REM print the REPL startup header
 602     REM save memory by printing this directly
 603     #cbm PRINT "Mal [C64 BASIC]"
 604     #qbasic PRINT "Mal [QBasic]"
 605
 606   REPL_LOOP:
 607     A$="user> ":GOSUB READLINE: REM call input parser
 608     IF EZ=1 THEN GOTO QUIT
 609     IF R$="" THEN GOTO REPL_LOOP
 610
 611     A$=R$:CALL REP: REM call REP
 612
 613     IF ER<>-2 THEN GOSUB PRINT_ERROR:GOTO REPL_LOOP
 614     PRINT R$
 615     GOTO REPL_LOOP
 616
 617   QUIT:
 618     REM GOSUB PR_MEMORY_SUMMARY_SMALL
 619     REM GOSUB PR_MEMORY_MAP
 620     REM P1=0:P2=ZI:GOSUB PR_MEMORY
 621     REM P1=D:GOSUB PR_OBJECT
 622     REM P1=ZK:GOSUB PR_OBJECT
 623     #cbm END
 624     #qbasic SYSTEM
 625
 626   PRINT_ERROR:
 627     REM if the error is an object, then print and free it
 628     IF ER>=0 THEN AZ=ER:B=0:GOSUB PR_STR:E$=R$:AY=ER:GOSUB RELEASE
 629     PRINT "Error: "+E$
 630     ER=-2:E$=""
 631     RETURN
 632