For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic state corresponding to a given buffer position. This function does that conveniently.
This function returns the parser state that the parser would reach at position pos starting from the beginning of the buffer. See Parser State, for a description of the parser state.
The return value is the same as if you call the low-level parsing
parse-partial-sexp to parse from the beginning of the
buffer to pos (see Low-Level Parsing). However,
syntax-ppss uses a cache to speed up the computation. Due to
this optimization, the second value (previous complete subexpression)
and sixth value (minimum parenthesis depth) in the returned parser
state are not meaningful.
This function has a side effect: it adds a buffer-local entry to
before-change-functions (see Change Hooks) for
syntax-ppss-flush-cache (see below). This entry keeps the
cache consistent as the buffer is modified. However, the cache might
not be updated if
syntax-ppss is called while
before-change-functions is temporarily let-bound, or if the
buffer is modified without running the hook, such as when using
inhibit-modification-hooks. In those cases, it is necessary to
This function flushes the cache used by
at position beg. The remaining arguments, ignored-args,
are ignored; this function accepts them so that it can be directly
used on hooks such as
before-change-functions (see Change Hooks).
Major modes can make
syntax-ppss run faster by specifying
where it needs to start parsing.
If this is non-
nil, it should be a function that moves to an
earlier buffer position where the parser state is equivalent to
nil—in other words, a position outside of any comment,
string, or parenthesis.
syntax-ppss uses it to further
optimize its computations, when the cache gives no help.