basic/step9_try.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 $INCLUDE: 'debug.in.bas'
  12
  13 REM READ(A$) -> R
  14 MAL_READ:
  15   GOSUB READ_STR
  16   RETURN
  17
  18 REM QUASIQUOTE(A) -> R
  19 SUB QUASIQUOTE
  20   REM pair?
  21   GOSUB TYPE_A
  22   IF T<6 OR T>7 THEN GOTO QQ_QUOTE
  23   IF (Z%(A+1)=0) THEN GOTO QQ_QUOTE
  24   GOTO QQ_UNQUOTE
  25
  26   QQ_QUOTE:
  27     REM ['quote, ast]
  28     B$="quote":T=5:GOSUB STRING
  29     B=R:A=A:GOSUB LIST2
  30     AY=B:GOSUB RELEASE
  31
  32     GOTO QQ_DONE
  33
  34   QQ_UNQUOTE:
  35     R=Z%(A+2)
  36     IF (Z%(R)AND 31)<>5 THEN GOTO QQ_SPLICE_UNQUOTE
  37     IF S$(Z%(R+1))<>"unquote" THEN GOTO QQ_SPLICE_UNQUOTE
  38       REM [ast[1]]
  39       R=Z%(Z%(A+1)+2)
  40       GOSUB INC_REF_R
  41
  42       GOTO QQ_DONE
  43
  44   QQ_SPLICE_UNQUOTE:
  45     GOSUB PUSH_A
  46     REM rest of cases call quasiquote on ast[1..]
  47     A=Z%(A+1):CALL QUASIQUOTE
  48     W=R
  49     GOSUB POP_A
  50
  51     REM set A to ast[0] for last two cases
  52     A=Z%(A+2)
  53
  54     REM pair?
  55     GOSUB TYPE_A
  56     IF T<6 OR T>7 THEN GOTO QQ_DEFAULT
  57     IF (Z%(A+1)=0) THEN GOTO QQ_DEFAULT
  58
  59     B=Z%(A+2)
  60     IF (Z%(B)AND 31)<>5 THEN GOTO QQ_DEFAULT
  61     IF S$(Z%(B+1))<>"splice-unquote" THEN QQ_DEFAULT
  62       REM ['concat, ast[0][1], quasiquote(ast[1..])]
  63
  64       B=Z%(Z%(A+1)+2)
  65       B$="concat":T=5:GOSUB STRING:C=R
  66       A=W:GOSUB LIST3
  67       REM release inner quasiquoted since outer list takes ownership
  68       AY=A:GOSUB RELEASE
  69       AY=C:GOSUB RELEASE
  70       GOTO QQ_DONE
  71
  72   QQ_DEFAULT:
  73     REM ['cons, quasiquote(ast[0]), quasiquote(ast[1..])]
  74
  75     Q=W:GOSUB PUSH_Q
  76     REM A set above to ast[0]
  77     CALL QUASIQUOTE
  78     B=R
  79     GOSUB POP_Q:W=Q
  80
  81     B$="cons":T=5:GOSUB STRING:C=R
  82     A=W:GOSUB LIST3
  83     REM release inner quasiquoted since outer list takes ownership
  84     AY=A:GOSUB RELEASE
  85     AY=B:GOSUB RELEASE
  86     AY=C:GOSUB RELEASE
  87   QQ_DONE:
  88 END SUB
  89
  90 REM MACROEXPAND(A, E) -> A:
  91 SUB MACROEXPAND
  92   GOSUB PUSH_A
  93
  94   MACROEXPAND_LOOP:
  95     REM list?
  96     GOSUB TYPE_A
  97     IF T<>6 THEN GOTO MACROEXPAND_DONE
  98     REM non-empty?
  99     IF Z%(A+1)=0 THEN GOTO MACROEXPAND_DONE
 100     B=Z%(A+2)
 101     REM symbol? in first position
 102     IF (Z%(B)AND 31)<>5 THEN GOTO MACROEXPAND_DONE
 103     REM defined in environment?
 104     K=B:CALL ENV_FIND
 105     IF R=-1 THEN GOTO MACROEXPAND_DONE
 106     B=R4
 107     REM macro?
 108     IF (Z%(B)AND 31)<>11 THEN GOTO MACROEXPAND_DONE
 109
 110     F=B:AR=Z%(A+1):CALL APPLY
 111     A=R
 112
 113     GOSUB PEEK_Q:AY=Q
 114     REM if previous A was not the first A into macroexpand (i.e. an
 115     REM intermediate form) then free it
 116     IF A<>AY THEN GOSUB PEND_A_LV
 117
 118     IF ER<>-2 THEN GOTO MACROEXPAND_DONE
 119     GOTO MACROEXPAND_LOOP
 120
 121   MACROEXPAND_DONE:
 122     GOSUB POP_Q: REM pop original A
 123 END SUB
 124
 125 REM EVAL_AST(A, E) -> R
 126 SUB EVAL_AST
 127   REM push A and E on the stack
 128   Q=E:GOSUB PUSH_Q
 129   GOSUB PUSH_A
 130
 131   IF ER<>-2 THEN GOTO EVAL_AST_RETURN
 132
 133   GOSUB TYPE_A
 134   IF T=5 THEN GOTO EVAL_AST_SYMBOL
 135   IF T>=6 AND T<=8 THEN GOTO EVAL_AST_SEQ
 136
 137   REM scalar: deref to actual value and inc ref cnt
 138   R=A
 139   GOSUB INC_REF_R
 140   GOTO EVAL_AST_RETURN
 141
 142   EVAL_AST_SYMBOL:
 143     K=A:GOTO ENV_GET
 144     ENV_GET_RETURN:
 145     GOTO EVAL_AST_RETURN
 146
 147   EVAL_AST_SEQ:
 148     REM setup the stack for the loop
 149     GOSUB MAP_LOOP_START
 150
 151     EVAL_AST_SEQ_LOOP:
 152       REM check if we are done evaluating the source sequence
 153       IF Z%(A+1)=0 THEN GOTO EVAL_AST_SEQ_LOOP_DONE
 154
 155       REM if we are returning to DO, then skip last element
 156       REM The EVAL_DO call to EVAL_AST must be call #2 for EVAL_AST to
 157       REM return early and for TCO to work
 158       Q=5:GOSUB PEEK_Q_Q
 159       IF Q=2 AND Z%(Z%(A+1)+1)=0 THEN GOTO EVAL_AST_SEQ_LOOP_DONE
 160
 161       REM call EVAL for each entry
 162       GOSUB PUSH_A
 163       IF T<>8 THEN A=Z%(A+2)
 164       IF T=8 THEN A=Z%(A+3)
 165       Q=T:GOSUB PUSH_Q: REM push/save type
 166       CALL EVAL
 167       GOSUB POP_Q:T=Q: REM pop/restore type
 168       GOSUB POP_A
 169       M=R
 170
 171       REM if error, release the unattached element
 172       REM TODO: is R=0 correct?
 173       IF ER<>-2 THEN AY=R:GOSUB RELEASE:R=0:GOTO EVAL_AST_SEQ_LOOP_DONE
 174
 175       REM for hash-maps, copy the key (inc ref since we are going to
 176       REM release it below)
 177       IF T=8 THEN N=M:M=Z%(A+2):Z%(M)=Z%(M)+32
 178
 179
 180       REM update the return sequence structure
 181       REM release N (and M if T=8) since seq takes full ownership
 182       C=1:GOSUB MAP_LOOP_UPDATE
 183
 184       REM process the next sequence entry from source list
 185       A=Z%(A+1)
 186
 187       GOTO EVAL_AST_SEQ_LOOP
 188     EVAL_AST_SEQ_LOOP_DONE:
 189       REM cleanup stack and get return value
 190       GOSUB MAP_LOOP_DONE
 191       GOTO EVAL_AST_RETURN
 192
 193   EVAL_AST_RETURN:
 194     REM pop A and E off the stack
 195     GOSUB POP_A
 196     GOSUB POP_Q:E=Q
 197 END SUB
 198
 199 REM EVAL(A, E) -> R
 200 SUB EVAL
 201   LV=LV+1: REM track basic return stack level
 202
 203   REM push A and E on the stack
 204   Q=E:GOSUB PUSH_Q
 205   GOSUB PUSH_A
 206
 207   REM PRINT "EVAL A:"+STR$(A)+",X:"+STR$(X)+",LV:"+STR$(LV)+",FRE:"+STR$(FRE(0))
 208
 209   EVAL_TCO_RECUR:
 210
 211   IF ER<>-2 THEN GOTO EVAL_RETURN
 212
 213   REM AZ=A:B=1:GOSUB PR_STR
 214   REM PRINT "EVAL: "+R$+" [A:"+STR$(A)+", LV:"+STR$(LV)+"]"
 215
 216   GOSUB LIST_Q
 217   IF R THEN GOTO APPLY_LIST
 218   EVAL_NOT_LIST:
 219   REM ELSE
 220     CALL EVAL_AST
 221     GOTO EVAL_RETURN
 222
 223   APPLY_LIST:
 224     CALL MACROEXPAND
 225
 226     GOSUB LIST_Q
 227     IF R<>1 THEN GOTO EVAL_NOT_LIST
 228
 229     GOSUB EMPTY_Q
 230     IF R THEN R=A:GOSUB INC_REF_R:GOTO EVAL_RETURN
 231
 232     A0=Z%(A+2)
 233
 234     REM get symbol in A$
 235     IF (Z%(A0)AND 31)<>5 THEN A$=""
 236     IF (Z%(A0)AND 31)=5 THEN A$=S$(Z%(A0+1))
 237
 238     IF A$="def!" THEN GOTO EVAL_DEF
 239     IF A$="let*" THEN GOTO EVAL_LET
 240     IF A$="quote" THEN GOTO EVAL_QUOTE
 241     IF A$="quasiquote" THEN GOTO EVAL_QUASIQUOTE
 242     IF A$="defmacro!" THEN GOTO EVAL_DEFMACRO
 243     IF A$="macroexpand" THEN GOTO EVAL_MACROEXPAND
 244     IF A$="try*" THEN GOTO EVAL_TRY
 245     IF A$="do" THEN GOTO EVAL_DO
 246     IF A$="if" THEN GOTO EVAL_IF
 247     IF A$="fn*" THEN GOTO EVAL_FN
 248     GOTO EVAL_INVOKE
 249
 250     EVAL_GET_A3:
 251       A3=Z%(Z%(Z%(Z%(A+1)+1)+1)+2)
 252     EVAL_GET_A2:
 253       A2=Z%(Z%(Z%(A+1)+1)+2)
 254     EVAL_GET_A1:
 255       A1=Z%(Z%(A+1)+2)
 256       RETURN
 257
 258     EVAL_DEF:
 259       REM PRINT "def!"
 260       GOSUB EVAL_GET_A2: REM set A1 and A2
 261
 262       Q=A1:GOSUB PUSH_Q
 263       A=A2:CALL EVAL: REM eval a2
 264       GOSUB POP_Q:A1=Q
 265
 266       IF ER<>-2 THEN GOTO EVAL_RETURN
 267
 268       REM set a1 in env to a2
 269       K=A1:C=R:GOSUB ENV_SET
 270       GOTO EVAL_RETURN
 271
 272     EVAL_LET:
 273       REM PRINT "let*"
 274       GOSUB EVAL_GET_A2: REM set A1 and A2
 275
 276       Q=A2:GOSUB PUSH_Q: REM push/save A2
 277       Q=E:GOSUB PUSH_Q: REM push env for for later release
 278
 279       REM create new environment with outer as current environment
 280       C=E:GOSUB ENV_NEW
 281       E=R
 282       EVAL_LET_LOOP:
 283         IF Z%(A1+1)=0 THEN GOTO EVAL_LET_LOOP_DONE
 284
 285         Q=A1:GOSUB PUSH_Q: REM push A1
 286         REM eval current A1 odd element
 287         A=Z%(Z%(A1+1)+2):CALL EVAL
 288         GOSUB POP_Q:A1=Q: REM pop A1
 289
 290         IF ER<>-2 THEN GOTO EVAL_LET_LOOP_DONE
 291
 292         REM set key/value in the environment
 293         K=Z%(A1+2):C=R:GOSUB ENV_SET
 294         AY=R:GOSUB RELEASE: REM release our use, ENV_SET took ownership
 295
 296         REM skip to the next pair of A1 elements
 297         A1=Z%(Z%(A1+1)+1)
 298         GOTO EVAL_LET_LOOP
 299
 300       EVAL_LET_LOOP_DONE:
 301         GOSUB POP_Q:AY=Q: REM pop previous env
 302
 303         REM release previous environment if not the current EVAL env
 304         GOSUB PEEK_Q_2
 305         IF AY<>Q THEN GOSUB RELEASE
 306
 307         GOSUB POP_Q:A2=Q: REM pop A2
 308         A=A2:GOTO EVAL_TCO_RECUR: REM TCO loop
 309
 310     EVAL_DO:
 311       A=Z%(A+1): REM rest
 312       GOSUB PUSH_A: REM push/save A
 313
 314       REM this must be EVAL_AST call #2 for EVAL_AST to return early
 315       REM and for TCO to work
 316       CALL EVAL_AST
 317
 318       REM cleanup
 319       AY=R: REM get eval'd list for release
 320
 321       GOSUB POP_A: REM pop/restore original A for LAST
 322       GOSUB LAST: REM get last element for return
 323       A=R: REM new recur AST
 324
 325       REM cleanup
 326       GOSUB RELEASE: REM release eval'd list
 327       AY=A:GOSUB RELEASE: REM release LAST value (not sure why)
 328
 329       GOTO EVAL_TCO_RECUR: REM TCO loop
 330
 331     EVAL_QUOTE:
 332       R=Z%(Z%(A+1)+2)
 333       GOSUB INC_REF_R
 334       GOTO EVAL_RETURN
 335
 336     EVAL_QUASIQUOTE:
 337       R=Z%(Z%(A+1)+2)
 338       A=R:CALL QUASIQUOTE
 339       A=R
 340       REM add quasiquote result to pending release queue to free when
 341       REM next lower EVAL level returns (LV)
 342       GOSUB PEND_A_LV
 343
 344       GOTO EVAL_TCO_RECUR: REM TCO loop
 345
 346     EVAL_DEFMACRO:
 347       REM PRINT "defmacro!"
 348       GOSUB EVAL_GET_A2: REM set A1 and A2
 349
 350       Q=A1:GOSUB PUSH_Q: REM push A1
 351       A=A2:CALL EVAL: REM eval A2
 352       GOSUB POP_Q:A1=Q: REM pop A1
 353
 354       REM change function to macro
 355       Z%(R)=Z%(R)+1
 356
 357       REM set A1 in env to A2
 358       K=A1:C=R:GOSUB ENV_SET
 359       GOTO EVAL_RETURN
 360
 361     EVAL_MACROEXPAND:
 362       REM PRINT "macroexpand"
 363       R=Z%(Z%(A+1)+2)
 364       A=R:CALL MACROEXPAND
 365       R=A
 366
 367       REM since we are returning it unevaluated, inc the ref cnt
 368       GOSUB INC_REF_R
 369       GOTO EVAL_RETURN
 370
 371     EVAL_TRY:
 372       REM PRINT "try*"
 373       GOSUB EVAL_GET_A1: REM set A1
 374
 375       GOSUB PUSH_A: REM push/save A
 376       A=A1:CALL EVAL: REM eval A1
 377       GOSUB POP_A: REM pop/restore A
 378
 379       GOSUB EVAL_GET_A2: REM set A1 and A2
 380
 381       REM if there is no error or catch block then return
 382       IF ER=-2 OR A2=0 THEN GOTO EVAL_RETURN
 383
 384       REM create environment for the catch block eval
 385       C=E:GOSUB ENV_NEW:E=R
 386
 387       A=A2:GOSUB EVAL_GET_A2: REM set A1 and A2 from catch block
 388
 389       REM create object for ER=-1 type raw string errors
 390       IF ER=-1 THEN B$=E$:T=4:GOSUB STRING:ER=R:GOSUB INC_REF_R
 391
 392       REM bind the catch symbol to the error object
 393       K=A1:C=ER:GOSUB ENV_SET
 394       AY=R:GOSUB RELEASE: REM release our use, env took ownership
 395
 396       REM unset error for catch eval
 397       ER=-2:E$=""
 398
 399       A=A2:CALL EVAL
 400
 401       GOTO EVAL_RETURN
 402
 403     EVAL_IF:
 404       GOSUB EVAL_GET_A1: REM set A1
 405       GOSUB PUSH_A: REM push/save A
 406       A=A1:CALL EVAL
 407       GOSUB POP_A: REM pop/restore A
 408       IF (R=0) OR (R=2) THEN GOTO EVAL_IF_FALSE
 409
 410       EVAL_IF_TRUE:
 411         AY=R:GOSUB RELEASE
 412         GOSUB EVAL_GET_A2: REM set A1 and A2 after EVAL
 413         A=A2:GOTO EVAL_TCO_RECUR: REM TCO loop
 414       EVAL_IF_FALSE:
 415         AY=R:GOSUB RELEASE
 416         REM if no false case (A3), return nil
 417         GOSUB COUNT
 418         IF R<4 THEN R=0:GOSUB INC_REF_R:GOTO EVAL_RETURN
 419         GOSUB EVAL_GET_A3: REM set A1 - A3 after EVAL
 420         A=A3:GOTO EVAL_TCO_RECUR: REM TCO loop
 421
 422     EVAL_FN:
 423       GOSUB EVAL_GET_A2: REM set A1 and A2
 424       T=10:L=A2:M=A1:N=E:GOSUB ALLOC: REM mal function
 425       GOTO EVAL_RETURN
 426
 427     EVAL_INVOKE:
 428       CALL EVAL_AST
 429
 430       REM if error, return f/args for release by caller
 431       IF ER<>-2 THEN GOTO EVAL_RETURN
 432
 433       REM push f/args for release after call
 434       GOSUB PUSH_R
 435
 436       AR=Z%(R+1): REM rest
 437       F=Z%(R+2)
 438
 439       REM if metadata, get the actual object
 440       GOSUB TYPE_F
 441       IF T=14 THEN F=Z%(F+1):GOSUB TYPE_F
 442
 443       ON T-8 GOTO EVAL_DO_FUNCTION,EVAL_DO_MAL_FUNCTION,EVAL_DO_MAL_FUNCTION
 444
 445       REM if error, pop and return f/args for release by caller
 446       GOSUB POP_R
 447       ER=-1:E$="apply of non-function":GOTO EVAL_RETURN
 448
 449       EVAL_DO_FUNCTION:
 450         REM regular function
 451         IF Z%(F+1)<60 THEN GOSUB DO_FUNCTION:GOTO EVAL_DO_FUNCTION_SKIP
 452         REM for recur functions (apply, map, swap!), use GOTO
 453         IF Z%(F+1)>60 THEN CALL DO_TCO_FUNCTION
 454         EVAL_DO_FUNCTION_SKIP:
 455
 456         REM pop and release f/args
 457         GOSUB POP_Q:AY=Q
 458         GOSUB RELEASE
 459         GOTO EVAL_RETURN
 460
 461       EVAL_DO_MAL_FUNCTION:
 462         Q=E:GOSUB PUSH_Q: REM save the current environment for release
 463
 464         REM create new environ using env and params stored in function
 465         C=Z%(F+3):A=Z%(F+2):B=AR:GOSUB ENV_NEW_BINDS
 466
 467         REM release previous env if it is not the top one on the
 468         REM stack (X%(X-2)) because our new env refers to it and
 469         REM we no longer need to track it (since we are TCO recurring)
 470         GOSUB POP_Q:AY=Q
 471         GOSUB PEEK_Q_2
 472         IF AY<>Q THEN GOSUB RELEASE
 473
 474         REM claim the AST before releasing the list containing it
 475         A=Z%(F+1):Z%(A)=Z%(A)+32
 476         REM add AST to pending release queue to free as soon as EVAL
 477         REM actually returns (LV+1)
 478         LV=LV+1:GOSUB PEND_A_LV:LV=LV-1
 479
 480         REM pop and release f/args
 481         GOSUB POP_Q:AY=Q
 482         GOSUB RELEASE
 483
 484         REM A set above
 485         E=R:GOTO EVAL_TCO_RECUR: REM TCO loop
 486
 487   EVAL_RETURN:
 488     REM AZ=R: B=1: GOSUB PR_STR
 489     REM PRINT "EVAL_RETURN R: ["+R$+"] ("+STR$(R)+"), LV:"+STR$(LV)+",ER:"+STR$(ER)
 490
 491     REM release environment if not the top one on the stack
 492     GOSUB PEEK_Q_1
 493     IF E<>Q THEN AY=E:GOSUB RELEASE
 494
 495     LV=LV-1: REM track basic return stack level
 496
 497     REM release everything we couldn't release earlier
 498     GOSUB RELEASE_PEND
 499
 500     REM trigger GC
 501     #cbm T=FRE(0)
 502     #qbasic T=0
 503
 504     REM pop A and E off the stack
 505     GOSUB POP_A
 506     GOSUB POP_Q:E=Q
 507
 508 END SUB
 509
 510 REM PRINT(A) -> R$
 511 MAL_PRINT:
 512   AZ=A:B=1:GOSUB PR_STR
 513   RETURN
 514
 515 REM RE(A$) -> R
 516 REM Assume D has repl_env
 517 REM caller must release result
 518 RE:
 519   R1=-1
 520   GOSUB MAL_READ
 521   R1=R
 522   IF ER<>-2 THEN GOTO RE_DONE
 523
 524   A=R:E=D:CALL EVAL
 525
 526   RE_DONE:
 527     REM Release memory from MAL_READ
 528     AY=R1:GOSUB RELEASE
 529     RETURN: REM caller must release result of EVAL
 530
 531 REM REP(A$) -> R$
 532 REM Assume D has repl_env
 533 SUB REP
 534   R2=-1
 535
 536   GOSUB RE
 537   R2=R
 538   IF ER<>-2 THEN GOTO REP_DONE
 539
 540   A=R:GOSUB MAL_PRINT
 541
 542   REP_DONE:
 543     REM Release memory from MAL_READ and EVAL
 544     AY=R2:GOSUB RELEASE
 545 END SUB
 546
 547 REM MAIN program
 548 MAIN:
 549   GOSUB INIT_MEMORY
 550
 551   LV=0
 552
 553   REM create repl_env
 554   C=0:GOSUB ENV_NEW:D=R
 555
 556   REM core.EXT: defined in Basic
 557   E=D:GOSUB INIT_CORE_NS: REM set core functions in repl_env
 558
 559   ZT=ZI: REM top of memory after base repl_env
 560
 561   REM core.mal: defined using the language itself
 562   A$="(def! not (fn* (a) (if a false true)))"
 563   GOSUB RE:AY=R:GOSUB RELEASE
 564
 565   A$="(def! load-file (fn* (f) (eval (read-file f))))"
 566   GOSUB RE:AY=R:GOSUB RELEASE
 567
 568   A$="(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs)"
 569   A$=A$+" (if (> (count xs) 1) (nth xs 1) (throw "+CHR$(34)+"odd number of"
 570   A$=A$+" forms to cond"+CHR$(34)+")) (cons 'cond (rest (rest xs)))))))"
 571   GOSUB RE:AY=R:GOSUB RELEASE
 572
 573   A$="(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs)"
 574   A$=A$+" `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
 575   GOSUB RE:AY=R:GOSUB RELEASE
 576
 577   REM load the args file
 578   A$="(def! -*ARGS*- (load-file "+CHR$(34)+".args.mal"+CHR$(34)+"))"
 579   GOSUB RE:AY=R:GOSUB RELEASE
 580
 581   IF ER>-2 THEN GOSUB PRINT_ERROR:END
 582
 583   REM set the argument list
 584   A$="(def! *ARGV* (rest -*ARGS*-))"
 585   GOSUB RE:AY=R:GOSUB RELEASE
 586
 587   REM get the first argument
 588   A$="(first -*ARGS*-)"
 589   GOSUB RE
 590
 591   REM no arguments, start REPL loop
 592   IF R<16 THEN GOTO REPL_LOOP
 593
 594   REM if there is an argument, then run it as a program
 595
 596   RUN_PROG:
 597     REM free up first arg because we get it again
 598     AY=R:GOSUB RELEASE
 599     REM run a single mal program and exit
 600     A$="(load-file (first -*ARGS*-))"
 601     GOSUB RE
 602     IF ER<>-2 THEN GOSUB PRINT_ERROR
 603     GOTO QUIT
 604
 605   REPL_LOOP:
 606     A$="user> ":GOSUB READLINE: REM call input parser
 607     IF EZ=1 THEN GOTO QUIT
 608     IF R$="" THEN GOTO REPL_LOOP
 609
 610     A$=R$:CALL REP: REM call REP
 611
 612     IF ER<>-2 THEN GOSUB PRINT_ERROR:GOTO REPL_LOOP
 613     PRINT R$
 614     GOTO REPL_LOOP
 615
 616   QUIT:
 617     REM GOSUB PR_MEMORY_SUMMARY_SMALL
 618     #cbm END
 619     #qbasic SYSTEM
 620
 621   PRINT_ERROR:
 622     REM if the error is an object, then print and free it
 623     IF ER>=0 THEN AZ=ER:B=0:GOSUB PR_STR:E$=R$:AY=ER:GOSUB RELEASE
 624     PRINT "Error: "+E$
 625     ER=-2:E$=""
 626     RETURN
 627