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35.6.3 Parser State

A parser state is a list of (currently) eleven elements describing the state of the syntactic parser, after it parses the text between a specified starting point and a specified end point in the buffer. Parsing functions such as syntax-ppss (see Position Parse) return a parser state as the value. Some parsing functions accept a parser state as an argument, for resuming parsing.

Here are the meanings of the elements of the parser state:

  1. The depth in parentheses, counting from 0. Warning: this can be negative if there are more close parens than open parens between the parser's starting point and end point.
  2. The character position of the start of the innermost parenthetical grouping containing the stopping point; nil if none.
  3. The character position of the start of the last complete subexpression terminated; nil if none.
  4. Non-nil if inside a string. More precisely, this is the character that will terminate the string, or t if a generic string delimiter character should terminate it.
  5. t if inside a non-nestable comment (of any comment style; see Syntax Flags); or the comment nesting level if inside a comment that can be nested.
  6. t if the end point is just after a quote character.
  7. The minimum parenthesis depth encountered during this scan.
  8. What kind of comment is active: nil if not in a comment or in a comment of style ‘a’; 1 for a comment of style ‘b’; 2 for a comment of style ‘c’; and syntax-table for a comment that should be ended by a generic comment delimiter character.
  9. The string or comment start position. While inside a comment, this is the position where the comment began; while inside a string, this is the position where the string began. When outside of strings and comments, this element is nil.
  10. The list of the positions of the currently open parentheses, starting with the outermost.
  11. When the last buffer position scanned was the (potential) first character of a two character construct (comment delimiter or escaped/char-quoted character pair), the syntax-code (see Syntax Table Internals) of that position. Otherwise nil.

Elements 1, 2, and 6 are ignored in a state which you pass as an argument to continue parsing. Elements 9 and 10 are mainly used internally by the parser code.

One additional piece of useful information is available from a parser state using this function:

— Function: syntax-ppss-toplevel-pos state

This function extracts, from parser state state, the last position scanned in the parse which was at top level in grammatical structure. “At top level” means outside of any parentheses, comments, or strings.

The value is nil if state represents a parse which has arrived at a top level position.