Description Henrik Lindberg 2010-06-03 09:31:26 EDT

I have been plagued for a while with getting "the required loop (...)+ at xxx" did not match any input, and have now figured out what I did in my (b3) grammar to trigger this.

With this grammar (where everything in the unordered group is optional):

BeeModel returns build::BeeModel hidden(WS, SL_COMMENT, ML_COMMENT) : {build::BeeModel}
    (imports += Import)*
    ( (functions += Function)  *
    & (concerns += Concern_Named) *
    & (propertySets += PropertySet_Named) *
    & (buildUnits += BuildUnit) *
    & (providers += TopLevelUnitProvider) ?
    & (repositories += Repository) *
    & (defaultProperties = PropertySetDefault) ?
    )?
    ;

If there is anything wrong while parsing the 'Function' rule - say it was given the faulty "function two : 1 + ;" b3 expression I get the "(...)+" error message and it marks the keyword "function". This is really bad when the function has many expressions and deep nesting.

If I however change the grammar to:

BeeModel returns build::BeeModel hidden(WS, SL_COMMENT, ML_COMMENT) : {build::BeeModel}
    (imports += Import) //*
    ( (functions += Function)  //*
    | (concerns += Concern_Named) //*
    | (propertySets += PropertySet_Named) //*
    | (buildUnits += BuildUnit) //*
    | (providers += TopLevelUnitProvider) //?
    | (repositories += Repository) //*
    | (defaultProperties = PropertySetDefault) //?
    )*
    ;

I get the correct error marker on the last '+' sign, and a meaningful error message.
(There are issues with this grammar, as two of the assignments will cause dangling instances as input may overwrite). The former grammar is also what I really want - I want the various statements to be grouped (i.e. all functions should be in one group), but the groups can be in any order. When input is correct, it correctly parses it this way.

This issue basically makes it impossible for me to use unordered groups.