Struct Context

pub struct Context<I: Stream> { /* private fields */ }

A high-level wrapper around an input Stream.

It handles errors, and tracks the Locations of the input Tokens that could form part of the next output Token. It also provides an unread() method to pretend that you didn’t read a Token.

Implementations

impl<I: Stream> Context<I>

pub fn new(input: I) -> Self

pub fn pop(&mut self) -> Location

Returns the Location of the most recent Token, and forgets it.

pub fn first(&self) -> Location

Returns the Location of the first Token returned by read().

pub fn last(&self) -> Location

Returns the Location of the last Token returned by read().

pub fn locate<T>(&self, value: T) -> Loc<T>

Annotate t with last().

pub fn drain(&mut self) -> Location

Returns a Location containing all Tokens read() so far, and forgets them.

pub fn read_any(&mut self) -> Result<Box<dyn Tree>, String>

Read the next Token and internally record its Location.

• Ok(tree) - The parse Tree of the next Token.
• Err(msg) - An error prevented parsing of the next Token.

pub fn read<T: Tree>(&mut self) -> Result<Option<Box<T>>, String>

Read the next Token and internally record its Location, but only if its parse Tree is of type T.

• Ok(Some(tree)) - The next Token’s parse tree is of type T.
• Ok(None) - The next Token is not a T. It has been unread().
• Err(message) - An error prevented parsing of the next Token.

pub fn read_if<T: Tree>( &mut self, is_wanted: impl FnOnce(&T) -> bool, ) -> Result<Option<Box<T>>, String>

Read the next Token and internally record its Location, but only if it is_wanted.

• Ok(Some(tree)) - If is_wanted(tree).
• Ok(None) - The next Token’s parse tree is not a T or is unwanted. It has been unread().
• Err(message) - An error prevented parsing of the next Token.

pub fn unread(&mut self, tree: Box<dyn Tree>)

Pretend we haven’t read the most recent Token.

tree must be the parse Tree of the most recent Token. It will be returned by the next call to read().