Quoth craven@gmx.net on Jul 12 at  9:43 am:
> This patch adds a new type sprinter_t, which is used for structured
> formatting, e.g. JSON or S-Expressions. The structure printer is the
> code from Austin Clements (id:87d34hsdx8.fsf@awakening.csail.mit.edu).
> 
> The structure printer contains the following function pointers:
> 
> /* start a new map/dictionary structure.
>  */
> void (*begin_map) (struct sprinter *);
> 
> /* start a new list/array structure
>  */
> void (*begin_list) (struct sprinter *);
> 
> /* end the last opened list or map structure
>  */
> void (*end) (struct sprinter *);
> 
> /* print one string/integer/boolean/null element (possibly inside a
>  * list or map
>  */
> void (*string) (struct sprinter *, const char *);
> void (*integer) (struct sprinter *, int);
> void (*boolean) (struct sprinter *, notmuch_bool_t);
> void (*null) (struct sprinter *);
> 
> /* print the key of a map's key/value pair.
>  */
> void (*map_key) (struct sprinter *, const char *);
> 
> /* print a frame delimiter (such as a newline or extra whitespace)
>  */
> void (*frame) (struct sprinter *);
> 
> The printer can (and should) use internal state to insert delimiters and
> syntax at the correct places.
> 
> Example:
> 
> format->begin_map(format);
> format->map_key(format, "foo");
> format->begin_list(format);
> format->integer(format, 1);
> format->integer(format, 2);
> format->integer(format, 3);
> format->end(format);
> format->map_key(format, "bar");
> format->begin_map(format);
> format->map_key(format, "baaz");
> format->string(format, "hello world");
> format->end(format);
> format->end(format);
> 
> would output JSON as follows:
> 
> {"foo": [1, 2, 3], "bar": { "baaz": "hello world"}}
> ---
>  sprinter.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
>  create mode 100644 sprinter.h
> 
> diff --git a/sprinter.h b/sprinter.h
> new file mode 100644
> index 0000000..1dad9a0
> --- /dev/null
> +++ b/sprinter.h
> @@ -0,0 +1,49 @@
> +#ifndef NOTMUCH_SPRINTER_H
> +#define NOTMUCH_SPRINTER_H
> +
> +/* for notmuch_bool_t */
> +#include "notmuch-client.h"
> +
> +/* Structure printer interface */
> +typedef struct sprinter
> +{
> +    /* start a new map/dictionary structure.
> +     */
> +    void (*begin_map) (struct sprinter *);
> +
> +    /* start a new list/array structure
> +     */
> +    void (*begin_list) (struct sprinter *);
> +
> +    /* end the last opened list or map structure
> +     */
> +    void (*end) (struct sprinter *);
> +
> +    /* print one string/integer/boolean/null element (possibly inside a
> +     * list or map
> +     */
> +    void (*string) (struct sprinter *, const char *);

Oh, also, the documentation for string should mention the string
argument should be UTF-8 encoded.

> +    void (*integer) (struct sprinter *, int);
> +    void (*boolean) (struct sprinter *, notmuch_bool_t);
> +    void (*null) (struct sprinter *);
> +
> +    /* print the key of a map's key/value pair.
> +     */
> +    void (*map_key) (struct sprinter *, const char *);
> +
> +    /* print a frame delimiter (such as a newline or extra whitespace)
> +     */
> +    void (*frame) (struct sprinter *);
> +} sprinter_t;
> +
> +/* Create a new structure printer that emits JSON */
> +struct sprinter *
> +sprinter_json_new(const void *ctx, FILE *stream);
> +
> +/* A dummy structure printer that signifies that standard text output is
> + * to be used instead of any structured format.
> + */
> +struct sprinter *
> +sprinter_text;
> +
> +#endif // NOTMUCH_SPRINTER_H