( regex.tal                                                        )
(                                                                  )
( compiles regex expression strings into regex nodes, then uses    )
( regex ndoes to match input strings.                              )
(                                                                  )
( this currently only supports matching an entire string, as       )
( opposed to searching for a matching substring, or extracting     )
( matching subgroups.                                              )
(                                                                  )
( regex node types:                                                )
(                                                                  )
(   NAME    DESCRIPTION                      STRUCT                )
(   empty   matches empty string             [ #01 next* ]         )
(   dot     matches any one char             [ #02 next* ]         )
(   lit     matches one specific char (c)    [ #03 c^ next* ]      )
(   or      matches either left or right     [ #04 left* right* ]  )
(   star    matches expr zero-or-more times  [ #05 r* next* ]      )
(           (NOTE: r.expr.next must be r)                          )
(                                                                  )
( `or` and `star` have the same structure and are handled by the   )
( same code (;do-or). however, the node types are kept different   )
( to make it clearer how to parse and assemble the nodes.          )
(                                                                  )
( concatenation isn't a node, it is implied by the *next addr.     )
( a next value of #0000 signals the end of the regex.              )
(                                                                  )
( in these docs str* is an address to a null-terminated string.    )
( regexes should not include nulls and cannot match them (other    )
( than the null which signals the end of a string).                )

%null? { #00 EQU }
%debug { #ff #0e DEO }
%emit { #18 DEO }
%space { #20 emit }
%newline { #0a emit }
%print { debug newline }
%error! { #00 #00 DIV }

( test -> )

|0100
    ;expr1 ;compile JSR2
    print
    ;emit-stack JSR2
    ;emit-arena JSR2
    newline

    ;test1 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test2 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test3 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test4 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test5 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test6 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test7 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    ;test8 OVR2k ;match JSR2 ;emit-byte JSR2 newline
    newline

    ;test1 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test2 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test3 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test4 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test5 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test6 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test7 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    ;test8 ;graph1 ;match JSR2 ;emit-byte JSR2 newline
    BRK

@match ( str* regex* -> bool^ )
    ;reset-stack JSR2
    ;loop JMP2

( we don't use the return stack here since that )
( complicates the back-tracking we need to do. )
( ultimately this code will issue a JMP2r to )
( return a boolean, which is where the stack )
( effects signature comes from. )

@loop ( s* r* -> bool^ )
    LDAk #01 EQU ;do-empty JCN2
    LDAk #02 EQU ;do-dot JCN2
    LDAk #03 EQU ;do-literal JCN2
    LDAk #04 EQU ;do-or JCN2
    LDAk #05 EQU ;do-or JCN2 ( same code as the or case )
    error!

@goto-backtrack ( -> bool^ )
    ;stack-exist JSR2 ,&has-stack JCN ( do we have stack? )
    #00 JMP2r ( no, return false )
    &has-stack
    ;pop4 JSR2
    ;goto-next JMP2 ( yes, resume from the top )

@goto-next ( str* next* -> bool^ )
    DUP2 #0000 GTH2 ,&has-next JCN
    POP2 LDA null? ,&end-of-string JCN
    ;goto-backtrack JMP2
    &end-of-string #01 JMP2r
    &has-next ;loop JMP2

@do-empty ( str* regex* -> bool^ )
    INC2 LDA2 ( load next )
    ;goto-next JMP2 ( jump to next )

@do-dot ( str* regex* -> bool^ )
    INC2 LDA2 STH2 ( load and stash next )
    LDAk #00 NEQ ,&non-empty JCN ( is there a char? )
    POP2r POP2 ;goto-backtrack JMP2 ( no, clear stacks and backtrack )
    &non-empty INC2 STH2r ;goto-next JMP2 ( yes, inc s, restore and jump )

@do-literal ( str* regex* -> bool^ )
    INC2
    LDAk STH ( store c )
    INC2 LDA2 STH2 ROTr ( store next, move c to top )
    LDAk
    STHr EQU ,&matches JCN ( do we match this char? )
    POP2r POP2 ;goto-backtrack JMP2 ( no, clear stacks and backtrack )
    &matches
    INC2 STH2r ;goto-next JMP2 ( yes, inc s, restore and jump )

( this also handles asteration, since it ends up having the same structure )
@do-or ( str* regex* -> bool^ )
    INC2 OVR2 OVR2 #0002 ADD2 ( s r+1 s r+3 )
    LDA2 ;push4 JSR2 ( save (s, right) in the stack for possible backtracking )
    LDA2 ;loop JMP2 ( continue on left branch )

( track the position in the input string )
@pos $2

( track how many levels deep we are in parenthesis )
@parens $2

( read and increments pos )
@read ( -> c^ )
    ;pos LDA2k ( pos s )
    LDAk STHk #00 EQU ( pos s c=0 [c] )
    ,&is-eof JCN ( pos s [c] )
    INC2 ( pos s+1 [c] )
    SWP2 STA2 ,&return JMP ( [c] )
    &is-eof POP2 POP2 
    &return STHr ( c ) JMP2r

( read pos )
@peek ( -> c^ )
    ;pos LDA2 LDA JMP2r

( TODO: [] + ? )
( compile an expression string into a regex graph )
@compile ( expr* -> regex* )
          ;pos    STA2
    #0000 ;parens STA2
    ;reset-stack JSR2
    ;compile-region JMP2

( the basic strategy here is to build a stack of non-or )
( expressions to be joined together at the end of the )
( region. each stack entry has two regex addresses: )
(   - the start of the regex )
(   - the current tail of the regex )
( when we concatenate a new node to a regex we update )
( the second of these but not the first. )
( )
( the bottom of the stack for a given region is denoted )
( by #ffff #ffff. above that we start with #0000 #0000 )
( to signal an empty node. )
@compile-region ( -> r2* )
    #ffff #ffff ;push4 JSR2 ( stack delimiter )
    #0000 #0000 ;push4 JSR2 ( stack frame start )
@compile-region-loop
    ;read JSR2
    DUP #00 EQU ;c-done JCN2
    DUP LIT '* EQU ;c-star JCN2
    DUP LIT '| EQU ;c-or   JCN2
    DUP LIT '. EQU ;c-dot  JCN2
    DUP LIT '( EQU ;c-lpar JCN2
    DUP LIT ') EQU ;c-rpar JCN2
    DUP LIT '\ EQU ;c-esc  JCN2
                   ;c-char JMP2

@c-done ( c^ -> r2* )
    POP
    ;parens LDA2 #0000 GTH2 ,&mismatched-parens JCN
    ;unroll-stack JSR2 POP2 JMP2r
    &mismatched-parens error!

@c-or ( c^ -> r2* )
    POP
    #0000 #0000 ;push4 JSR2
    ;compile-region-loop JMP2

@c-lpar ( c^ -> r2* )
    POP
    ;parens LDA2 INC2 ;parens STA2 ( parens++ )
    ;compile-region JMP2

@c-rpar ( c^ -> r2* )
    POP
    ;parens LDA2 #0000 EQU2 ,&mismatched-parens JCN
    ;parens LDA2 #0001 SUB2 ;parens STA2 ( parens-- )
    ;unroll-stack JSR2
    ;push-next JSR2
    ;compile-region-loop JMP2
    &mismatched-parens error!

@c-dot ( c^ -> r2* )
    POP
    ;alloc-dot JSR2 DUP2 ;push-next JSR2
    ;compile-region-loop JMP2

@c-char ( c^ -> r2* )
    ;alloc-lit JSR2
    DUP2 ;push-next JSR2
    ;compile-region-loop JMP2

( TODO: escaping rules not quite right )
@c-esc ( c^ -> r2* )
    POP
    ;read JSR2
    ;c-char JMP2

@c-star ( c^ -> regex* )
    POP
    ;pop4 JSR2 SWP2 STH2 STH2k ( x1 [x0 x1] )
    ;alloc-star JSR2 ( r )
    STH2r STH2kr ( r x1 x0 [x0] )
    ;remove-from JSR2 ( r [x0] )
    STH2r OVR2 OVR2 ( r x0 r x0 ) ;set-next JSR2
    OVR2 #0003 ADD2 #0000 SWP2 STA2 ( fixme: manually zeroing next )
    ( r x0 ) SWP2 ;push4 JSR2
    ;compile-region-loop JMP2


( allocate node types ------ )

@alloc3 ( mode^ -> r* )
    #0000 ROT ( 00 00 mode^ )
    #03 ;alloc JSR2 ( 00 00 mode^ addr* ) ( LIT 'a emit print )
    STH2k STA
    STH2kr INC2 STA2
    STH2r
    JMP2r

@alloc-empty ( -> r* )
    #01 ;alloc3 JMP2

@alloc-dot ( -> r* )
    #02 ;alloc3 JMP2

@alloc-lit ( c^ -> r* )
    #03 #0000 SWP2
    #04 ;alloc JSR2
    STH2k STA
    STH2kr INC2 STA
    STH2kr #0002 ADD2 STA2
    STH2r
    JMP2r

@alloc-or ( right* left* -> r* )
    #05 ;alloc JSR2 STH2 ( r l [x] )
    #04 STH2kr            STA ( r l [x] )
        STH2kr       INC2 STA2 ( r [x] )
        STH2kr #0003 ADD2 STA2 ( [x] )
    STH2r JMP2r

@alloc-star ( expr* -> r* )
    #05 ;alloc JSR2 STH2  ( expr [r] )
    #05 STH2kr STA        ( expr [r] )
    DUP2 STH2kr INC2 STA2 ( expr [r] )
    #0000 STH2kr #0003 ADD2 STA2 ( expr [r] )
    STH2kr SWP2 ( r expr [r] )
    ;set-next JSR2 ( [r] )
    STH2r JMP2r

( unroll one part of the parsing stack, returning )
( a single node consisting of an alternation of )
( all elements on the stack. )
( )
( this unrolls until it hits #ffff #ffff, which it )
( also removes from the stack. )
@unroll-stack ( -> start* end* )
    ;pop4 JSR2 STH2 ( r )
    #00 STH ( count items in stack frame )
    DUP2 #0000 NEQ2 ,&loop JCN ;alloc-empty JSR2
    &loop ( r* )
    ;pop4 JSR2 POP2 ( r x )
    DUP2 #ffff EQU2 ( r x x-is-end? ) ,&done JCN
    INCr ( items++ )
    ;alloc-or JSR2 ( r|x ) ,&loop JMP
    &done
    ( r ffff )
    POP2
    STHr ,&is-or JCN
    STH2r JMP2r
    &is-or
    POP2r
    ;alloc-empty JSR2 OVR2 OVR2 SWP2 ( r empty empty r )
    ;set-next JSR2
    JMP2r

( add r to the top of the stock. )
( )
( in particular, this will write r into tail.next )
( before replacing tail with r. )
@push-next ( r0 r1 -> )
    ;pop4 JSR2 ( r0 r1 x0 x1 )
    DUP2 #0000 EQU2 ( r0 r1 x0 x1 x1=0? ) ,&is-zero JCN
    STH2 ROT2 STH2r ( r1 x0 r0 x1 )
    ;set-next JSR2 SWP2 ( x0 r1 )
    ;push4 JSR2
    JMP2r
    &is-zero POP2 POP2 ;push4 JSR2 JMP2r

@set-next-addr ( target* addr* -> )
    LDA2k #0000 EQU2 ( target addr addr=0? ) ,&is-zero JCN
    LDA2 ;set-next JSR2 JMP2r
    &is-zero STA2 JMP2r

( set regex.next to target )
@set-next ( target* regex* -> )
(    LIT 'n emit space LDAk ;emit-byte JSR2 print )
        LDAk #01 NEQ ,&!1 JCN       INC2 ( STA2 ) ( LIT 't emit print ) ;set-next-addr JSR2 JMP2r
    &!1 LDAk #02 NEQ ,&!2 JCN       INC2 ( STA2 ) ;set-next-addr JSR2 JMP2r
    &!2 LDAk #03 NEQ ,&!3 JCN #0002 ADD2 ( STA2 ) ( LIT 'y emit print )  ;set-next-addr JSR2 JMP2r
    &!3 LDAk #04 NEQ ,&!4 JCN
(        LIT 'w emit print )
(            INC2k      LDA2 space LIT '{ emit DUP2 ;emit-short JSR2 ;set-next JSR2
            #0003 ADD2 LDA2 space LIT '} emit DUP2 ;emit-short JSR2 ;set-next JSR2 JMP2r )
            OVR2 OVR2 INC2 ( LIT '{ emit space ) ;set-next-addr JSR2
                #0003 ADD2 ( LIT '} emit space ) ;set-next-addr JSR2 JMP2r
    &!4 LDAk #05 NEQ ,&!5 JCN #0003 ADD2 ( STA2 ) ;set-next-addr JSR2 JMP2r
    &!5 ( LIT '? emit LDAk ;emit-byte JSR2 ) error!

@remove-addr ( target* addr* -> )
(    LIT 'A emit print )
    LDA2k #0000 EQU2 ( t a v=0? ) ,&is-zero JCN
    OVR2 OVR2 LDA2 EQU2 ( t a t=v? ) ,&is-equal JCN
    LDA2 ( t v ) ;remove-from JSR2 JMP2r
    &is-zero ( LIT 'r emit print ) POP2 POP2 JMP2r
    &is-equal ( LIT 's emit print ) NIP2 #0000 SWP2 STA2 JMP2r

( remove target from regex )
@remove-from ( target* regex* -> )
(    LIT 'R emit print )
        LDAk #01 NEQ ,&!1 JCN       INC2 ;remove-addr JSR2 JMP2r
    &!1 LDAk #02 NEQ ,&!2 JCN       INC2 ;remove-addr JSR2 JMP2r
    &!2 LDAk #03 NEQ ,&!3 JCN #0002 ADD2 ;remove-addr JSR2 JMP2r
    &!3 LDAk #04 NEQ ,&!4 JCN
(        LIT 'Q emit print )
            OVR2 OVR2 INC2 ;remove-addr JSR2
(        LIT 'q emit print )
                #0003 ADD2 ;remove-addr JSR2 JMP2r
    &!4 LDAk #05 NEQ ,&!5 JCN #0003 ADD2 ;remove-addr JSR2 JMP2r
    &!5 ( LIT '? emit LDAk ;emit-byte JSR2 ) error!

( test cases -------- )

( corresponds to regex: a(b|c)d* )
@expr1 "a(b|c)d* 00

( corresponds to regex: a(b|c)d* )
( accepts "ab" or "ac" followd by any number of d's )
@graph1
        03 'a :x1
    @x1 04 :x2 :x3
    @x2 03 'b :x4
    @x3 03 'c :x4
    @x4 05 :x5 0000
    @x5 03 'd :x4

@test1 "ab 00 ( yes )
@test2 "acdd 00 ( yes )
@test3 "add 00 ( no )
@test4 "abd 00 ( yes )
@test5 "acddddddddddd 00 ( yes )
@test6 "bd 00 ( no )
@test7 "z 00 ( no )
@test8 00 ( no )

( emit byte/short )

@emit-short ( byte -- )
    SWP ;emit-byte JSR2 ;emit-byte JSR2 JMP2r

@emit-byte ( byte -- )
    DUP #04 SFT ,&hex JSR #0f AND ,&hex JMP
    &hex #30 ADD DUP #39 GTH #27 MUL ADD emit
    JMP2r

( stack operations ---- )

( @peek2 ( -> regex* )
    ;assert-exist JSR2 ( check for space )
    ;stack-pos LDA2 ( load stack-pos )
    #0002 SUB2 LDA2 ( get regex )
    JMP2r )

@push4 ( str* regex* -> )
    ;assert-avail JSR2 ( check for space )
    ;stack-pos LDA2 #0002 ADD2 STA2 ( cell[2:3] <- regex )
    ;stack-pos LDA2 STA2 ( cell[0:1] <- str )
    ;stack-pos LDA2 #0004 ADD2 ;stack-pos STA2 ( pos += 4 )
    JMP2r

( @peek4 ( -> str* regex* )
    ;assert-exist JSR2 ( check for space )
    ;stack-pos LDA2 ( load stack-pos )
    #0002 SUB2 LDA2k STH2 ( pop and stash regex )
    #0002 SUB2 LDA2  STH2r ( pop the str, restore the regex )
    JMP2r )

@pop4 ( -> str* regex* )
    ;assert-exist JSR2 ( check for space )
    ;stack-pos LDA2 ( load stack-pos )
    #0002 SUB2 LDA2k STH2 ( pop and stash regex )
    #0002 SUB2 LDA2k STH2 ( pop and stash str )
    ;stack-pos STA2 ( save new stack-pos )
    STH2r STH2r ( restore str and regex )
    JMP2r

@reset-stack ( -> )
    ;stack-bot ;stack-pos STA2 JMP2r ( pos <- 0 )

@stack-avail ( -> bool^ )
    ;stack-pos LDA2 ;stack-top LTH2 JMP2r
@stack-exist ( -> bool^ )
    ;stack-pos LDA2 ;stack-bot GTH2 JMP2r
@assert-avail ( -> )
    ;stack-avail JSR2 ,&ok JCN error! &ok JMP2r
@assert-exist ( -> )
    ;stack-exist JSR2 ,&ok JCN error! &ok JMP2r

@emit-stack ( -> )
    space LIT 'n emit LIT '= emit ;stack-pos LDA2 ;stack-bot SUB2 #0004 DIV2 ;emit-short JSR2 LIT ': emit
    ;stack-bot
    &loop
    DUP2 ;stack-pos LDA2 LTH2 ,&ok JCN
    POP2 newline JMP2r
    &ok
    space LDA2k ;emit-short JSR2
    #0002 ADD2 ,&loop JMP

@stack-pos :stack-bot ( the next position to insert at )
@stack-bot $1000 @stack-top ( holds 1024 steps (4096 bytes) )

( arena operations ---- )

@reset-arena ( -> )
    ;arena-bot ;arena-pos STA2 JMP2r

@alloc ( size^ -> addr* )
    #00 SWP ( size* )
    ;arena-pos LDA2 STH2k ADD2 ( pos+size* {pos} )
    ( TODO: ensure we don't exceed our space )
    ;arena-pos STA2 ( pos <- pos+size )
    STH2r JMP2r ( return old pos )

|1ffe
@arena-pos :arena-bot ( the next position to allocate )
@arena-bot $400 @arena-top ( holds up to 1024 bytes )

@emit-n ( addr* count^ -> addr2* )
    DUP #00 GTH ( addr count count>0? ) ,&ok JCN ( addr count ) POP newline JMP2r
    &ok
    STH ( addr [count] ) space LDAk ;emit-byte JSR2 INC2 ( addr+1 [count] )
    STHr #01 SUB ( addr+1 count-1 )
    ;emit-n JMP2

@emit-arena ( -> )
    ;arena-bot
    &loop
(    print )
    DUP2 ;arena-pos LDA2 LTH2 ,&ok JCN POP2 JMP2r
    &ok
    DUP2 ;emit-short JSR2
    LIT ': emit space
        LDAk #01 NEQ ,&!1 JCN #03 ;emit-n JSR2 ,&loop JMP
    &!1 LDAk #02 NEQ ,&!2 JCN #03 ;emit-n JSR2 ,&loop JMP
    &!2 LDAk #03 NEQ ,&!3 JCN #04 ;emit-n JSR2 ,&loop JMP
    &!3 LDAk #04 NEQ ,&!4 JCN #05 ;emit-n JSR2 ,&loop JMP
    &!4 LDAk #05 NEQ ,&!5 JCN #05 ;emit-n JSR2 ,&loop JMP
    &!5 ( LDAk ;emit-byte JSR2 LIT '! emit newline ) error!