[rules-users] Catch 22 ANTLR DSL matching issue

Hi Droolers, Regarding this blurb from the 5.2 DSL reference: "It is important to note that the compiler transforms DSL rule files line by line. In the above example, all the text after "Something is " to the end of the line is captured as the replacement value for "{colour}", and this is used for interpolating the target string. This may not be exactly what you want. For instance, when you intend to merge different DSL expressions to generate a composite DRL pattern, you need to transform a DSLR line in several independent operations. The best way to achieve this is to ensure that the captures are surrounded by characteristic text - words or even single characters. As a result, the matching operation done by the parser plucks out a substring from somewhere within the line. In the example below, quotes are used as distinctive characters. Note that the characters that surround the capture are not included during interpolation, just the contents between them." Given this DSL (test_expander.dsl) [when](C|c)heese is "{type}"=Cheese(type=="{type}") [when](is|hails|comes) from {country}=Cheese(country=="{country}") [then]Add the message {message}=System.out.println({message}); And this DSLR package com.sample import com.sample.DroolsTest.Cheese; expander test_expander.dsl rule "rule_1" when Cheese is "cheddar" and is from Italy then Add the message "Cheddar IS from Italy" end rule "rule_2" when cheese is cheddar and comes from Italy then Add the message "Cheddar COMES from Italy" end I know that rule_2 fails because I removed the “distinctive characters” so ANTLR is confused on what to capture. It just seems so unnatural for a rule author to have to somehow magically know to add quotes in order to merge different DSL expressions to generate a composite DRL pattern. The documentation suggests also surrounding it with distinctive words so I sneak an “and” into the DSL entry. [when](C|c)heese is {type} and=Cheese(type=="{type}") This allows me to write my rules more naturally. rule "rule_1" when Cheese is cheddar and is from Italy then Add the message "Cheddar IS from Italy" end rule "rule_2" when cheese is cheddar and comes from Italy then Add the message "Cheddar COMES from Italy" end In the first example the “and” in Cheese is "cheddar" and is from Italy is actually a logical AND - not a matching character – which is nice because we can use it to logically connect the 2 expressions or just match the first DSL expression by itself as in Cheese is cheddar And since the second expression is not present we can drop the quotes. (But how on earth will a rule author know this?). But if we add the “and” as part of the first DSL expression 1) It is no longer a connecting logical character but is part of the expression to match (yuk) 2) We can no longer just write “Cheese is cheddar” by itself but are forced to write “Cheese is cheddar and” if we want to match only the first expression. You might as well just combined the two expressions into one since there is no real advantage now to having two expressions! One nice thing would be for the Guvnor DSL editor to 1)try the capture greedily first, 2)get the annoying “no viable alternative error”, 3)CATCH the error instead of just giving up, 4)capture non-greedily and match only the first word, 5)then search for matching DSL expressions beyond that. Or something like that. The only time you should have to add quotes is if the text you are matching actually contains multiple words. Anything else is counter-intuitive. Please tell me the planned replacement for DSL addresses this! Jeff -- View this message in context: http://drools.46999.n3.nabble.com/Catch-22-ANTLR-DSL-matching-issue-tp299... Sent from the Drools: User forum mailing list archive at Nabble.com.