** This code is Copyright (c) 2002, by the authors of nmh. See the
** COPYRIGHT file in the root directory of the nmh distribution for
** complete copyright information.
+**
+** This code compiles the format strings (documented in mh-format(5)) into
+** an internal form to be later processed by fmt_scan.c.
+**
+** What happens here is that the format strings are parsed and an array
+** of struct format structures are returned. Each format structure is
+** a single operation interpreted by the the routines in fmt_scan.c.
+**
+** There is a NOT a one-to-one correspondence between format strings and
+** format instructions; some functions have side effects that can result
+** in multiple instructions being generated. The exact list of instructions
+** generated by a format string can be seem with the nmh fmtdump utility.
+**
+** A list of format instructions can be found in fmt_compile.h.
+**
+** If you wish to add a new function, you will need to do the following
+** things:
+**
+** - Add a new instruction to the list of instructions in fmt_compile.h.
+** Note that test instructions (starting with FT_IF_S_NULL) have special
+** handling, so if you are NOT writing a test function then you need
+** to insert it into the list before that _and_ bump all of the
+** following instruction numbers.
+**
+** - Add the function name to the functable[] array below, and write any
+** special code that your function may require in terms of parsing
+** (it very well may not need anything).
+**
+** - Add the code in fmt_scan.c to handle your new function.
+**
+** - Document the new function in the mh-format(5) man page.
+**
*/
#include <h/mh.h>
#define TFL_PUTS 1 /* implicit putstr if top level */
#define TFL_PUTN 2 /* implicit putnum if top level */
+/*
+** The functable array maps between the text names of format functions and
+** the format instructions interpreted by the engine in fmt_scan.c.
+**
+** The elements of this structure are as follows:
+**
+** name: The name of the function as seen in the format string. This is
+** what maps a particular function name into a format instruction.
+** type: The type of argument this function expects. Those types are
+** listed above (with the TF_ prefix). This affects what gets
+** placed in the format instruction (the f_un union).
+** f_type: The instruction corresponding to this function (from the list
+** in fmt_compile.h).
+** extra: Used by some functions to provide extra data to the compiler.
+** Uses include:
+** - Providing an alternate instruction to combine a load
+** and test operation (see do_if()).
+** - Passed in f_value in the format instruction to provide
+** extra information for the engine (see FT_LV_DAT handling
+** in fmt_scan.c).
+** - Provide a hint as to preprocessing that is required for
+** this instruction (see do_name()).
+** flags: See the definitions for TFL_PUTS & TFL_PUTN above.
+*/
struct ftable {
char *name; /* function name */
char type; /* argument type */
static char *do_if(char *);
+/*
+** Lookup a function name in the functable
+*/
static struct ftable *
lookup(char *name)
{
** Return the number of header components found in the format
** string.
*/
-
int
fmt_compile(char *fstring, struct format **fmt)
{
}
+/*
+** Process functions & components (handle field width here as well
+*/
static char *
do_spec(char *sp)
{
return (cp);
}
+
+/*
+** Process a component name. Normally this involves generating an FT_COMP
+** instruction for the specified component. If preprocess is set, then we
+** do some extra processing.
+*/
static char *
do_name(char *sp, int preprocess)
{
return (cp);
}
+
+/*
+** Generate one or more instructions corresponding to the named function.
+** The different type of function arguments are handled here.
+*/
static char *
do_func(char *sp)
{
return (cp);
}
+
+/*
+** Handle an expression as an argument. Basically we call one of do_name(),
+** do_func(), or do_if()
+*/
static char *
do_expr(char *sp, int preprocess)
{
return (cp);
}
+
+/*
+** I am guessing this was for some kind of loop statement, which would have
+** looked like %[ .... %]. It looks like the way this would have worked
+** is that the format engine would have seen that FT_DONE had a 1 in the
+** f_un.f_un_value and then decided whether or not to continue the loop.
+** There is no support for this in the format engine, so right now if
+** you try using it you will reach the FT_DONE and simply stop. I'm leaving
+** this here in case someone wants to continue the work.
+*/
static char *
do_loop(char *sp)
{
return cp;
}
+
+/*
+** Handle an if-elsif-endif statement. Note here that the branching
+** is handled by the f_skip member of the struct format (which is really
+** just f_width overloaded). This number controls how far to move forward
+** (or back) in the format instruction array.
+*/
static char *
do_if(char *sp)
{
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