34.6.1 Motion Commands Based on Parsing

This section describes simple point-motion functions that operate based on parsing expressions.

Function: scan-lists from count depth

This function scans forward count balanced parenthetical groupings from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.

If depth is nonzero, treat the starting position as being depth parentheses deep. The scanner moves forward or backward through the buffer until the depth changes to zero count times. Hence, a positive value for depth has the effect of moving out depth levels of parenthesis from the starting position, while a negative depth has the effect of moving deeper by -depth levels of parenthesis.

Scanning ignores comments if parse-sexp-ignore-comments is non-nil.

If the scan reaches the beginning or end of the accessible part of the buffer before it has scanned over count parenthetical groupings, the return value is nil if the depth at that point is zero; if the depth is non-zero, a scan-error error is signaled.

Function: scan-sexps from count

This function scans forward count sexps from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.

Scanning ignores comments if parse-sexp-ignore-comments is non-nil.

If the scan reaches the beginning or end of (the accessible part of) the buffer while in the middle of a parenthetical grouping, an error is signaled. If it reaches the beginning or end between groupings but before count is used up, nil is returned.

Function: forward-comment count

This function moves point forward across count complete comments (that is, including the starting delimiter and the terminating delimiter if any), plus any whitespace encountered on the way. It moves backward if count is negative. If it encounters anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. This includes (for instance) finding the end of a comment when moving forward and expecting the beginning of one. The function also stops immediately after moving over the specified number of complete comments. If count comments are found as expected, with nothing except whitespace between them, it returns t; otherwise it returns nil.

This function cannot tell whether the “comments” it traverses are embedded within a string. If they look like comments, it treats them as comments.

To move forward over all comments and whitespace following point, use (forward-comment (buffer-size)). (buffer-size) is a good argument to use, because the number of comments in the buffer cannot exceed that many.