nxu/regex.tal

( 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 }
%quit! { #01 #0f DEO BRK }

( ERROR HANDLING )

( using error! will print the given message before causing )
( the interpreter to halt. )
@error! ( msg* -> )
    LIT '! emit space
    &loop LDAk ,&continue JCN ,&done JMP
    &continue LDAk emit INC2 ,&loop JMP
    &done POP2 newline quit!

( error messages )
@unknown-node-type "unknown 20 "node 20 "type 00
@mismatched-parens "mismatched 20 "parenthesis 00
@stack-is-full "stack 20 "is 20 "full 00
@stack-is-empty "stack 20 "is 20 "empty 00
@arena-is-full "arena 20 "is 20 "full 00
@star-invariant "star 20 "invariant 20 "failed 00

( REGEX MATCHING )

( use stored regex to match against a stored string. )
( )
( regex* should be the address of a compiled regex )
( such as that returned from ;compile. )
( )
( str* should be a null-terminated string. )
( )
( returns true if the string, and false otherwise. )
@match ( str* regex* -> bool^ )
    ;reset-stack JSR2
    ;loop JMP2

( loop used during matching )
( )
( 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 )
    ;unknown-node-type ;error! JSR2

( used when we hit a dead-end during matching. )
( )
( if stack is non-empty we have a point we can resume from. )
@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 )

( follow the given address (next*) to continue matching )
@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

( handle the empty node -- just follow the next pointer ) 
@do-empty ( str* regex* -> bool^ )
    INC2 LDA2 ( load next )
    ;goto-next JMP2 ( jump to next )

( handle dot -- match any one character )
@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 )

( handle literal -- match one specific character )
@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 )

( handle or -- try the left branch but backtrack to the right if needed )
( )
( 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 )

( REGEX PARSING )

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

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

( read and increment 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

( is pos currently pointing to a star? )
@peek-to-star ( -> is-star^ )
    ;pos LDA2 LDA LIT '* EQU JMP2r

( just increment pos )
@skip
    ;pos LDA2 INC2 ;pos STA2 JMP2r

( TODO: )
( 1. character groups: [] and [^] )
( 2. one-or-more: + )
( 3. zero-or-one: ? )
( 4. symbolic escapes, e.g. \n )

( STRETCH GOALS: )
( a. ^ and $ )
( b. counts: {n} and {m,n} )
( c. substring matching, i.e. searching )
( d. subgroup extraction )
( e. back-references, e.g \1 )

( compile an expression string into a regex graph )
( )
( the regex will be allocated in the arena; if there is not )
( sufficient space an error will be thrown. )
( )
( the stack will also be used during parsing although unlike )
( the arena it will be released once compilation ends. )
@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-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
    DUP LIT '* EQU ;c-star JCN2 
                   ;c-char JMP2

( either finalize the given r0/r1 or else wrap it in )
( a star node if a star is coming up next. )
( )
( we use this look-ahead approach rather than compiling )
( star nodes directly since the implementation is simpler. )
@c-peek-and-finalize ( r0* r1* -> r2* )
    ;peek-to-star JSR2 ( r0 r1 next-is-star? )
    ,&next-is-star JCN ,&finally JMP ( r0 r1 )
    &next-is-star ;skip JSR2 POP2 ;alloc-star JSR2 DUP2 ( star )
    &finally ;push-next JSR2 ;compile-region-loop JMP2

( called when we reach EOF of the input string )
( )
( as with c-rpar we have to unroll the current level )
( of the stack, building any or-nodes that are needed. )
( )
( this is where we detect unclosed parenthesis. )
@c-done ( c^ -> r2* )
    POP
    ;parens LDA2 #0000 GTH2 ,&mismatched-parens JCN
    ;unroll-stack JSR2 POP2 JMP2r
    &mismatched-parens ;mismatched-parens ;error! JSR2

( called when we read "|" )
( )
( since we defer building or-nodes until the end of the region )
( we just start a new stack frame and continue. )
@c-or ( c^ -> r2* )
    POP
    #0000 #0000 ;push4 JSR2
    ;compile-region-loop JMP2

( called when we read "(" )
( )
( this causes us to: )
( )
(  1. increment parens )
(  2. start a new region on the stack )
(  3. jump to compile-region to start parsing the new region )
@c-lpar ( c^ -> r2* )
    POP
    ;parens LDA2 INC2 ;parens STA2 ( parens++ )
    ;compile-region JMP2

( called when we read ")" )
( )
( this causes us to: )
( )
(  1. check for mismatched parens )
(  2. decrement parens )
(  3. unroll the current region on the stack into one regex node )
(  4. finalize that node and append it to the previous region )
(  5. continue parsing ) 
@c-rpar ( c^ -> r2* )
    POP
    ;parens LDA2 #0000 EQU2 ,&mismatched-parens JCN
    ;parens LDA2 #0001 SUB2 ;parens STA2 ( parens-- )
    ;unroll-stack JSR2
    ;c-peek-and-finalize JMP2
    &mismatched-parens ;mismatched-parens ;error! JSR2

( called when we read "." )
( )
( allocates a dot-node and continues. )
@c-dot ( c^ -> r2* )
    POP
    ;alloc-dot JSR2 ( dot )
    DUP2 ;c-peek-and-finalize JMP2

( TODO: escaping rules not quite right )

( called when we read "\" )
( )
( allocates a literal of the next character. )
( )
( this doesn't currently handle any special escape sequences. )
@c-esc ( c^ -> r2* )
    POP
    ;read JSR2
    ;c-char JMP2

( called when we read any other character )
( )
( allocates a literal-node and continues. )
@c-char ( c^ -> r2* )
    ;alloc-lit JSR2 ( lit )
    DUP2 ;c-peek-and-finalize JMP2

( called if we parse a "*" )
( )
( actually calling this means the code broke an invariant somewhere. )
@c-star ( c^ -> regex* )
    POP
    ;star-invariant ;error! JSR2

( ALLOCATING REGEX NDOES )

@alloc3 ( mode^ -> r* )
    #0000 ROT ( 00 00 mode^ )
    #03 ;alloc JSR2 ( 00 00 mode^ addr* )
    STH2k STA ( addr <- mode )
    STH2kr INC2 STA2 ( addr+1 <- 0000 )
    STH2r JMP2r ( return addr )

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

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

@alloc-lit ( c^ -> r* )
    #03 #0000 SWP2 ( 0000 c^ 03 )
    #04 ;alloc JSR2 ( 0000 c^ 03 addr* )
    STH2k STA ( addr <- 03 )
    STH2kr INC2 STA ( addr+1 <- c )
    STH2kr #0002 ADD2 STA2 ( addr+2 <- 0000 )
    STH2r JMP2r ( return addr )

@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 region 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

( load the given address:  )
( )
(  1. if it points to 0000, update it to target )
(  2. otherwise, call set-next on it )
@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* -> )
        LDAk #01 NEQ ,&!1 JCN       INC2 ;set-next-addr JSR2 JMP2r
    &!1 LDAk #02 NEQ ,&!2 JCN       INC2 ;set-next-addr JSR2 JMP2r
    &!2 LDAk #03 NEQ ,&!3 JCN #0002 ADD2  ;set-next-addr JSR2 JMP2r
    &!3 LDAk #04 NEQ ,&!4 JCN
            ( todo: this is probably broken )
            OVR2 OVR2 INC2 ;set-next-addr JSR2
                #0003 ADD2 ;set-next-addr JSR2 JMP2r
    &!4 LDAk #05 NEQ ,&!5 JCN #0003 ADD2 ;set-next-addr JSR2 JMP2r
    &!5 ;unknown-node-type ;error! JSR2

( STACK OPERATIONS )
( )
( we always push/pop 4 bytes at a time. the stack has a fixed )
( maximum size it can use, defined by ;stack-top. )
( )
( the stack can be cleared using ;reset-stack, which resets )
( the stack pointers but does not zero out any memory. )

( push 4 bytes onto the stack )
@push4 ( str* regex* -> )
    ;assert-stack-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

( pop 4 bytes from the stack )
@pop4 ( -> str* regex* )
    ;assert-stack-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 pointers )
@reset-stack ( -> )
    ;stack-bot ;stack-pos STA2 JMP2r ( pos <- 0 )

( can more stack be allocated? )
@stack-avail ( -> bool^ )
    ;stack-pos LDA2 ;stack-top LTH2 JMP2r

( is the stack non-empty? )
@stack-exist ( -> bool^ )
    ;stack-pos LDA2 ;stack-bot GTH2 JMP2r

( error if stack is full )
@assert-stack-avail ( -> )
    ;stack-avail JSR2 ,&ok JCN ;stack-is-full ;error! JSR2 &ok JMP2r

( error is stack is empty )
@assert-stack-exist ( -> )
    ;stack-exist JSR2 ,&ok JCN ;stack-is-empty ;error! JSR2 &ok JMP2r

( stack-pos points to the next free stack position (or the top if full). )
@stack-pos :stack-bot ( the next position to insert at )

( stack-bot is the address of the first stack position. )
( stack-top is the address of the first byte beyond the stack. )
@stack-bot $1000 @stack-top ( holds 1024 steps (4096 bytes) )

( ARENA OPERATIONS )
( )
( the arena represents a heap of memory that can easily be )
( allocated in small amounts. )
( )
( the entire arena can be reclaimed using ;reset-arena, but )
( unlike systems such as malloc/free, the arena cannot relcaim )
( smaller amounts of memory. )
( )
( the arena is used to allocate regex graph nodes, which are )
( dynamically-allocated as the regex string is parsed. once )
( a regex is no longer needed the arena may be reclaimed. )

( reclaim all the memory used by the arena )
@reset-arena ( -> )
    ;arena-bot ;arena-pos STA2 JMP2r

( currently caller is responsible for zeroing out memory if needed )
@alloc ( size^ -> addr* )
    #00 SWP ( size* )
    ;arena-pos LDA2 STH2k ADD2 ( pos+size* [pos] )
    DUP2 ;arena-top GTH2 ( pos+size pos+size>top? [pos] )
    ,&error JCN ( pos+size [pos] )
    ;arena-pos STA2 ( pos += size [pos] )
    STH2r JMP2r ( pos )
    &error POP2 POP2r ;arena-is-full ;error! JSR2

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