combinator

parsley.errors.combinator$

This module contains combinators that can be used to directly influence error messages of parsers.

Error messages are, by default, not particularly descriptive. However, the combinators in this module can be used to improve the generation of error messages by providing labels for expected items, explanations for why things went wrong, custom error messages, custom unexpected error messages, as well as correcting the offsets that error messages actually occurred at.

Attributes

Since:: 3.0.0
Source:: combinator.scala
Graph
Supertypes: class Object
trait Matchable
class Any
Self type: combinator.type

Members list

Concise view

Failure Combinators

These combinator immediately fail the parser, with a more bespoke message.

This combinator consumes no input and fails immediately with the given error messages.

Produces a specialised error message where all the lines of the error are the given msgs in order of appearance.

Attributes

msg0

the first message in the error message.

msgs

the remaining messages that will make up the error message.

Returns:

a parser that fails producing an error message consisting of all the given messages.

Since:

3.0.0

Example:

val failing = fail("hello,", "this is an error message", "broken across multiple lines")

Source:

combinator.scala

This combinator consumes no input and fails immediately with the given error messages.

Produces a specialised error message where all the lines of the error are the given msgs in order of appearance.

Attributes

caretWidth

the size of the caret for this error: should ideally match the width of the cause of the error.

msg0

the first message in the error message.

msgs

the remaining messages that will make up the error message.

Returns:

a parser that fails producing an error message consisting of all the given messages.

Since:

4.0.0

Example:

val failing = fail("hello,", "this is an error message", "broken across multiple lines")

Source:

combinator.scala

This combinator consumes no input and fails immediately, setting the unexpected component to the given item.

Produces a trivial error message where the unexpected component of the error is replaced with the given item item.

Attributes

item: the unexpected message for the error generated.
Returns:: a parser that fails producing an error with item as the unexpected token.
Since:: 3.0.0
Source:: combinator.scala

This combinator consumes no input and fails immediately, setting the unexpected component to the given item.

Produces a trivial error message where the unexpected component of the error is replaced with the given item item.

Attributes

caretWidth: the size of the caret for this error: should ideally match the width of the cause of the error (the unexpected item).
item: the unexpected message for the error generated.
Returns:: a parser that fails producing an error with item as the unexpected token.
Since:: 4.0.0
Source:: combinator.scala

Error Extension Combinators

These are implicit classes that, when in scope, enable additional combinators on parsers that interact with the error system in some way.

This class exposes helpful combinators that are specialised for generating more helpful errors messages.

This extension class operates on values that are convertible to parsers. It enables the use of error combinators, which can be used for data validation, error annotation, or immediate failing.

Attributes

P: the type of base value that this class is used on (the conversion to Parsley) is summoned automatically.
con: a conversion that allows values convertible to parsers to be used.
p: the value that this class is enabling methods on.
Constructor:: This constructor should not be called manually, it is designed to be used via Scala's implicit resolution.
Version:: 3.0.0
Source:: combinator.scala
Graph
Supertypes: class Object
trait Matchable
class Any

This class exposes helpful combinators that are specialised for generating more helpful errors messages.

This extension class operates on values that are convertible to parsers. It enables the use of error combinators, which can be used for data validation, error annotation, or immediate failing.

Attributes

P: the type of base value that this class is used on (the conversion to Parsley) is summoned automatically.
con: a conversion that allows values convertible to parsers to be used.
p: the value that this class is enabling methods on.
Constructor:: This constructor should not be called manually, it is designed to be used via Scala's implicit resolution.
Version:: 3.0.0
Source:: combinator.scala

Error Adjustment Combinators

These combinators can affect at what position an error is caused at. They are opposites: where amend will ensure an error message is said to have generated at the position on entry to the combinator, entrench will resist these changes.

This combinator adjusts any error messages generated by the given parser so that they occur at the position recorded on entry to this combinator (effectively as if no input were consumed).

This is useful if validation work is done on the output of a parser that may render it invalid, but the error should point to the beginning of the structure. This combinators effect can be cancelled with entrench.

Attributes

p: a parser whose error messages should be adjusted.
Returns:: a parser that parses p but ensures any errors generated occur as if no input were consumed.
Since:: 3.1.0
Source:: combinator.scala

This combinator prevents the action of any enclosing amend on the errors generated by the given parser.

Sometimes, the error adjustments performed by amend should only affect errors generated within a certain part of a parser and not the whole thing; in this case, entrench can be used to protect sub-parsers from having their errors adjusted, providing a much more fine-grained scope for error adjustment.

Attributes

p

a parser whose error messages should not be adjusted by any surrounding amend.

Returns:

a parser that parses p but ensures any error messages are generated normally.

Since:

3.1.0

Example:

In this example, the ident parser should not allow keywords, and these error messages should be generated from the start of the identifier, not the end. However any errors generated within the identifier itself should remain at their regular offsets.

val ident = amend {
   entrench(stringOfSome(letter)).filterOut {
       case v if keywords.contains(v) => s"keyword &#36;v cannot be an identifier"
   }
}

Source:

combinator.scala

This combinator marks any errors within the given parser as being lexical errors.

When an error is marked as a lexical error, it sets a flag within the error that is passed to ErrorBuilder.unexpectedToken: this should be used to prevent Lexer-based token extraction from being performed on an error, since lexing errors cannot be the result of unexpected tokens.

Attributes

p: the parser that serves as a token.
Returns:: a parser that parses p but ensures any error messages are marked as lexical errors.
Since:: 4.0.0
Source:: combinator.scala

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