Error

Marks this result as consuming.

Marks this result as non-consuming.

Sets this parser's label.

Note that this only happens on non-consuming parsers: if the parser consumed data, then he's not one the possible outcomes of a disjunction, but the right branch of the disjunction. It just happened to fail.

Take for example:

val parser = string("foo") | string("bar")
parser.run("foa")

In this context, bar is clearly not a possibility - we've started parsing foo succesfully, and we want a message like "Expected o, found a". Applying the label to a consuming result would, instead, yield "Expected foo, found a", which is less useful.