class

Sthx::Ahead

Inherits Sthx::Rule < Reference < Object

Forward declaration of a rule.

Constructors

new(*, __file = __FILE__, __line = __LINE__) : Ahead
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Instance methods

advance(cursor : Cursor, data : TreeData, *, collect : Collect) : Advance::Result

Performs cursor motion and returns the result, one of Advance::Result: success Advance::Ok or failure Advance::Err.

data is the TreeData object built so far.

To implementors of this method: in case of failure to commit, cursor must be rolled back to its state before calling this method. In other words, advance is implemented in a "transaction" kind of way. Intermediate results and changes must never be available to the caller. This method either succeeds and mutates the cursor; or it fails and leaves the cursor intact.

Source
put(rule : Rule) : self

Assigns rule, should be called when its definition becomes available.

expr = ahead
expr.put('(' & maybe(expr) & ')')

expr.apply?("(((())))") # => Tree
expr.apply?("((())")    # => nil
Source