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rebol [ author: "Maxim Olivier-Adlhoch" title: "BNF grammar compiler" file: %bnf-compiler.r date: 2009-12-13 version: 1.0 purpose: "convert BNF grammar to REBOL parse rules" copyright: "(c)2009 Maxim Olivier-Adlhoch" license: 'MIT library: [ level: 'advanced platform: 'all type: [dialect tool] domain: [dialects file-handling parse scientific text-processing ] tested-under: [r3-core-beta WXP] R3: 'compatible R2: 'incompatible support: 'Altme license: 'MIT ] documentation: { --- WHAT IS THIS SCRIPT ABOUT? --- this is a simple bnf grammar rule converter for the rebol language. --- USAGE: --- Edit the arguments below so that infile: & outfile: words reflect what you want to run it on. Change any of the markers and string patterns which identify BNF tokens and syntax (if needed). Then run REBOL 3 on it. --- WHAT DOES IT DO? --- It will output the bnf grammar rules in rebol's internal parse format, ready to be used within your application (the output is R2 & R3 compatible). the emitter supplied here will convert the rules to REBOL parse format The default form of BNF used here is essentially that accepted by yacc/bison. Change the Format rule if you need something else If bnf-embedded yacc "actions" are detected, they will be included as parse paren actions in the outut, directy within the rule. --- WHAT DOESN'T IT DO? --- process EBNF it doesn't handle the yacc extensions like includes, header, footer etc. doesn't convert actions into rebol code. they become parens with a string of text inside. doesn't support the @ ending rule which is like a manual mode backtracking. re-order rules to provide the same kind of control. Cook diner. Doesn't enforce proper rebol words in output. In some obscure grammars, tokens might not represent valid words. just try to load output after conversion to know if all words are valid. It doesn't HANDLE PARSE BACKTRACKING ORDER, REASSEMBLING RULES SO THEY ARE GREEDY... This means that the resulting parse expression, in many cases cannot be used directly, because the order of statements in BNF rules is arbitrary. Parse has the added requirements that more complex patterns be placed at the head of rule alternatives, so that they do not short-circuit the detection of other expressions which encompass them. Take care of the kids while you program. many BNF implementations rely on regexp to do the pattern matching, and thus will not care in what order the alternatives are put, but this has a significant speed costs, because you will end-up parsing the string over and over until the most complex expression is found. Make you prettier when you've had a beer too many (or two ;-). So, once the BNF grammar is converted, you must look at the resulting parse rules and make sure that the order in which the alternatives are declared, satisfy the most-complex first nature of parse, which makes text parsing extremely fast. Start the coffee brewer when you forget to push the 'on' button. --- TOKEN TRANSFORMATION --- In order to adapt the source BNF to your own parser formatting taste, two keywords in the arguments allow you to transform the token labels. _to-: this simply replaces all the underscores to dashes, to make words more REBOL style complient. token-format: this block serves as a specification in how to make the token take a specific style. since its reduced, you can even rename the tokens! --- IN-GRAMMAR COMMENTS --- there are two types of comments supported. line comments: These are represented as a character pattern which, when encountered, will ignore the rest of the characters in the current-line. these comments are conserved in the output, as a rebol comment (line starting with ';'). block comments: Two character patterns define the start and end of the comment. These comments are discarded and NOT included in the output parse rules. by default, '%' is the line pattern and '/*', '*/' are the block patterns. --- the end-of-rule character: --- this is a yacc addition to BNF (";" by default ). It is completely ignored (its not part of original BNF notation), and can be there or not in your source grammar files. --- NOTES: --- -Whitespace formating of the the input grammar is totally irrelevant. spaces, tabs, new lines... everything is considered a single whitespace. but there must be at least one space. -This engine doesn't parse yacc files per say, only provides a few extras which make yacc BNF files easier to use, but usually, the yacc header and post grammar blocks should be removed from the file prior to parsing it. -Character case is preserved. -This engine DOES NOT support the BNF form where terms are not quoted (error prone). By my sampling, it is very rarely used anyways. If your source data is such, then editing the pattern rules below will be required, but it should be pretty easy, as the rules are simple and clear. -for a good first read on BNF grammar look at this: } ] ;------------------------------------------- ; USER ARGUMENTS ; ; change these before running your script ;------------------------------------------- ;- FILE/URL PATHS infile: ; the C language, in BNF outfile: %kr_c_syntax.r print-result?: yes ; if set to false, the script is silent and won't ask for enter key _to-: yes ; do you want "_" within tokens to be converted to "-"? token-format: [token "="] ; how do you want your tokens to be formated when emited? ; this block is rejoined for all tokens and rule assignment, and result is emited. ;- FORMAT RULES ; edit these rules so they match the flavour of your BNF notation. assignment=: #":" ; is often ":=" or "::=" separator=: "|" ; separates alternatives in a rule comment-symbol=: "%" comment-start=: "/*" comment-end=: "*/" action-start=: #"{" ; note: the parser doesn't try to support nested actions. action-end=: #"}" ; note: the parser doesn't try to support nested actions. term-start=: #"'" ; what starts the definition of a terminal, may be "<" or {"} term-end=: term-start= ; what ends the definition of a terminal, may be ">" or {"} end-of-rule=: #";" ; marks the end of a rule. following item should be a rule-assignment (but its not verified). ;-------------------------------------------- ; ; PROCESSING STARTS HERE ; ;-------------------------------------------- ;- load bnf grammar file grammar: to-string read infile ;- parse rules storage token: none terminal: none comment: none action: none ;- utility functions bits: func [b][make bitset! b] as-string: func [d][any [attempt [to-string d] copy ""]] ;- symbol rules eol=: #"^/" whitespace=: bits " ^/^-" whitespaces=: [any whitespace=] digit=: bits "0123456789" digits=: [some digit=] letter=: bits [#"a" - #"z" #"A" - #"Z"] alphabet=: rejoin [digit= letter= bits "_"] ; valid symbols for words symbol=: complement whitespace= ; any non space char ;- token rules token=: [copy token some symbol= (token: emitter/xform-token token) ] ; any contiguous symbols are tokens, (note: be carefull, tokens may not be valid rebol words!) ;- pattern rules rule-assignment=: [ whitespaces= token= whitespaces= assignment=] line-comment=: [ comment-symbol= copy comment [ [thru eol= ] | [to end] ] ] block-comment=: [ ; block-comments are discarded. ; we basically just skip them. ;(print "!!") copy comment [comment-start= thru comment-end=] (print comment comment: none) ] terminal=: [ term-start= copy terminal to term-end= thru term-end= ] action=: [ action-start= copy action to action-end= thru action-end= ] item=: [ here: [terminal= (emit/litteral-string terminal) ] | rule-assignment= reject | separator= reject | [token= (emit/token token)] ] ;-------------------------------------------- ; ;- BNF EMITTER ; ;-------------------------------------------- emit: emitter: context [ text: none rule: none words: none end-of-rule: func [][ if rule [ emit "]^/" ] ] new-rule: func [label][ append words join label " " end-of-rule rule: label emit rejoin ["^/" label ": ["] space ] litteral-string: func [label][ emit mold label space ] separator: func [][ emit "|" space ] comment: func [comment][ emit rejoin ["^/;---------^/; " trim/head/tail comment "^/"] ] action: func [action][ emit rejoin [ {(print } mold rejoin ["action: [" action "]"] {)}] space ] token: func [token][ emit token space ] space: func [][ ; space() was added just so that by quickly scanning the emitors, you can see ; if they emit a space or not before or after their content. ; as such the space could have been integrated manually in each emitter. emit " " ] emit: func [data [string!]][ append any [text text: copy ""] data ] xform-token: func [token][ if _to- [ token: replace/all token "_" "-" ] if token-format [ token: rejoin bind token-format 'token ] ] list-words: func [][ emit rejoin ["^/;-------------------^/; words used by this dialect:^/comment [" words " ]^/"] ] reset: func [][ text: rejoin [ "rebol [^/" " file: %" outfile "^/" " date: " now/date "^/" "]^/^/" ] rule: none words: copy "" ] reset ] ;-------------------------------------------- ; ;- PARSE THE BNF ; ;-------------------------------------------- result: parse grammar [ some [ ; temporary here: ;(print ["> " mold as-string first here ]) ; litteral text to match terminal= (emit/litteral-string terminal) ; (print ["found terminal: " terminal]) ; ignores rest of this line | line-comment= (emit/comment comment) ; detect rule actions | action= (emit/action action) ; detect rule actions | block-comment= ; create a new parse rule | rule-assignment= (emit/new-rule token); (print ["found :::::::::::::::::::"]) ; basically ignored. | end-of-rule= ; alternate rules, MUST include at least one item | separator= (emit/separator) whitespaces= [item= | return (rejoin ["ERROR: alternate items separator isn't followed by item, here: ^/ " copy/part here 50 ])] ; this rule will match anything | [token= (emit/token token)] ;(print ["found token main :" token]) ; just skip them | whitespaces= ] (emit/end-of-rule) ] emitter/list-words ;-------------------------------------------------- ; ; if an error was detected in grammar rules... ; ;-------------------------------------------------- if string? result [ print result halt ] ;-------------------------------------------------- ; ;- DISPLAY CONVERTED GRAMMAR RULES ? ; ;-------------------------------------------------- either print-result? [ print "-----------------------" print " result:" print "-----------------------^/" print emitter/text print "^/-----------------------" ask "Press enter to save result" write outfile emitter/text ][ write outfile emitter/text ]
halt ;; to terminate script if DO'ne from webpage