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| 1 | +ECPG modifies and extends the core grammar in a way that |
| 2 | +1) every token in ECPG is <str> type. New tokens are |
| 3 | + defined in ecpg.tokens, types are defined in ecpg.type |
| 4 | +2) most tokens from the core grammar are simply converted |
| 5 | + to literals concatenated together to form the SQL string |
| 6 | + passed to the server, this is done by parse.pl. |
| 7 | +3) some rules need side-effects, actions are either added |
| 8 | + or completely overridden (compared to the basic token |
| 9 | + concatenation) for them, these are defined in ecpg.addons, |
| 10 | + the rules for ecpg.addons are explained below. |
| 11 | +4) new grammar rules are needed for ECPG metacommands. |
| 12 | + These are in ecpg.trailer. |
| 13 | +5) ecpg.header contains common functions, etc. used by |
| 14 | + actions for grammar rules. |
| 15 | + |
| 16 | +In "ecpg.addons", every modified rule follows this pattern: |
| 17 | + ECPG: dumpedtokens postfix |
| 18 | +where "dumpedtokens" is simply tokens from core gram.y's |
| 19 | +rules concatenated together. e.g. if gram.y has this: |
| 20 | + ruleA: tokenA tokenB tokenC {...} |
| 21 | +then "dumpedtokens" is "ruleAtokenAtokenBtokenC". |
| 22 | +"postfix" above can be: |
| 23 | +a) "block" - the automatic rule created by parse.pl is completely |
| 24 | + overridden, the code block has to be written completely as |
| 25 | + it were in a plain bison grammar |
| 26 | +b) "rule" - the automatic rule is extended on, so new syntaxes |
| 27 | + are accepted for "ruleA". E.g.: |
| 28 | + ECPG: ruleAtokenAtokenBtokenC rule |
| 29 | + | tokenD tokenE { action_code; } |
| 30 | + ... |
| 31 | + It will be substituted with: |
| 32 | + ruleA: <original syntax forms and actions up to and including |
| 33 | + "tokenA tokenB tokenC"> |
| 34 | + | tokenD tokenE { action_code; } |
| 35 | + ... |
| 36 | +c) "addon" - the automatic action for the rule (SQL syntax constructed |
| 37 | + from the tokens concatenated together) is prepended with a new |
| 38 | + action code part. This code part is written as is's already inside |
| 39 | + the { ... } |
| 40 | + |
| 41 | +Multiple "addon" or "block" lines may appear together with the |
| 42 | +new code block if the code block is common for those rules. |
| 43 | + |
