parsley/parsley/parsley.errors/combinator

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

Grouped members

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.

Value parameters

msg0: the first message in the error message.
msgs: the remaining messages that will make up the error message.

Attributes

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.

Value parameters

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.

Attributes

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.

Value parameters

item: the unexpected message for the error generated.

Attributes

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.

Value parameters

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.

Attributes

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.

Type parameters

P: the type of base value that this class is used on (the conversion to Parsley) is summoned automatically.

Value parameters

con: a conversion that allows values convertible to parsers to be used.
p: the value that this class is enabling methods on.

Attributes

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
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.

Type parameters

P: the type of base value that this class is used on (the conversion to Parsley) is summoned automatically.

Value parameters

con: a conversion that allows values convertible to parsers to be used.
p: the value that this class is enabling methods on.

Attributes

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.

Value parameters

p: a parser whose error messages should be adjusted.

Attributes

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 first tries to amend the position of any error generated by the given parser, and if the error was entrenched will dislodge it instead.

Value parameters

p: a parser whose error messages should be amended unless its been entrenched.

Attributes

Returns: a parser that parses p but ensures any errors generated occur as if no input were consumed.
See also: amend and dislodge
Since: 4.2.0
Source: combinator.scala

This combinator undoes the action of the entrench combinator on the given parser.

Entrenchment is important for preventing the incorrect amendment of certain parts of sub-errors for a parser, but it may be then undesireable to block further amendments from elsewhere in the parser. This combinator can be used to cancel and entrenchment after the critical section has passed.

Value parameters

p: a parser that should no longer be under the affect of an entrench combinator

Attributes

Returns: a parser that parses p and allows its error messages to be amended.
Since: 4.2.0
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.

Value parameters

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

Attributes

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.