\section{Prettyprinting}

\subsection{API for prettyprinting}

Here is a suitable API for a prettyprinter for noweb.
Input to be prettyprinted is a sequence of strings, newlines, and
chunks used.  A [[STRING]] is always free of newlines.
<<API for prettyprinter>>=
typedef enum parttype {
  START_OF_CHUNK=1, END_OF_CHUNK, STRING, USE_CHUNK, NEWLINE,
  LITERAL, DEFINITION, WHATSIT
} Parttype;
@ The prettyprinter calls back into the application as follows:
<<API for prettyprinter>>=
typedef void (*PrettyPrinterCallback) (void *closure, Parttype type, char *contents);
@ The [[contents]] must be
\begin{quote}
\begin{tabular}{ll}
[[START_OF_CHUNK]]&The name of the chunk being prettyprinted\\
[[END_OF_CHUNK]]&[[NULL]]\\
[[STRING]]&A string with no newlines\\
[[LITERAL]]${}^*$&A string with no newlines, to get no further formatting\\
[[USE_CHUNK]]&The name of the chunk referred to\\
[[NEWLINE]]&[[NULL]]\\
[[DEFINITION]]${}^*$&An identifier whose definition is in this chunk.\\
[[WHATSIT]]&An uninterpreted string passed to the callback function
\end{tabular}
\end{quote}
Items marked with a star ($*$) are legal only when the prettyprinter
is calling back into the application.
The identifier given in [[DEFINITION]] isn't printed, so if the
prettyprinter wants to print it, it has to send it twice.
@
The prettyprinter exports two calls to the application.
<<API for prettyprinter>>=
typedef struct prettyprinter *PrettyPrinter;

extern PrettyPrinter new_prettyprinter(PrettyPrinterCallback callback, void *closure);
extern void prettyprint(PrettyPrinter pp, Parttype type, char *contents);
@ The prettyprinter accepts calls to the [[prettyprint]] procedure.
Any call to [[prettyprint]] may result in one or more callbacks to the
procedure registered when [[new_prettyprinter]] is called.
For any given [[PrettyPrinter]], the application must call
[[prettyprint]] with [[type==END_OF_CHUNK]] exactly once, and that
call must be the last call.

<<header>>=
<<API for prettyprinter>>
@
\subsection{Calling the prettyprinter}

The assumption here is that we have zero or more prettyprinters
satisfying the interface above---what are the mechanics of getting
something prettyprinted.
We select a prettyprinter based on
the name of the root chunk.

Because we want to support either a two-pass or one-pass algorithm,
we don't say how lines will come in or go out, but we do say that we
will strip all the trailing newlines.
<<definitions>>=
void pretty (char *getline(void *in), void *in,
             void  putline(void *out, char *line), void *out,
             PrettyPrinter make_pp(void *cl, char *name), void *cl)
{
    char *line = NULL;          /* buffer for input */
    PrettyPrinter pp;
    Location loc;

    while ((line = getline(in)) != NULL) {
	<<adjust [[loc]] if needed>>
	<<if not [[@begin code]], copy line and [[continue]]>>
	putline(out, line);

        for (line = getline(in);
             line && !is_keyword(line,"defn") && !is_keyword(line,"text");
             line = getline(in)
        ) putline(out, line);
        insist(line,"defn","code chunk had no definition line");
	putline(out, line);
        pp = make_pp(cl, line+6); /* use chunk name */
	/* FG: added following line to let prettyprinter know what
         * chunk it's prettyprinting. */
	if (pp) prettyprint(pp, START_OF_CHUNK, line+6);
        if (!pp) { <<copy code chunk to [[out]]>>; continue; }

        for (; line && !is_keyword(line, "nl") ;) {
          line = getline(in); putline(out, line);
        }
        insist(line,"nl","definition line not followed by newline");
        loc.lineno++;
	for (line = getline(in);
             line != NULL && !is_end(line,"code");
             line = getline(in))
        {
            <<adjust [[loc]] if needed>>
            if (is_keyword(line,"nl")) {
                prettyprint(pp, NEWLINE, NULL);
            } else if (is_keyword(line,"text")) {
                prettyprint(pp, STRING, line+1+4+1);
            } else if (is_keyword(line,"use")) {
                prettyprint(pp, USE_CHUNK, line+1+3+1);
            } else {
                prettyprint(pp, WHATSIT, line);
            }
        }
	prettyprint(pp, END_OF_CHUNK, NULL);
        <<if [[line==NULL]] die of premature end of file>>
	putline(out, line);
    }
}
<<if not [[@begin code]], copy line and [[continue]]>>=
if (!is_begin(line, "code")) {
    putline(out, line);
    continue;
}
<<copy code chunk to [[out]]>>=
while ((line = getline(in)) != NULL) {
    putline(out, line);
    if (is_end(line, "code")) break;
}
@
<<adjust [[loc]] if needed>>=
{ if (is_keyword(line, "nl") || is_index(line, "nl")) {
      loc.lineno++;
  } else if (is_keyword(line,"file")) {
      loc.filename = strsave(line + 6);
      loc.lineno = 1;
  } else if (is_keyword(line, "line")) {
      <<save line number from [[line]] ([[@line ...]]) into [[loc.lineno]]>>
      loc.lineno--;
  }
}
@
<<save line number from [[line]] ([[@line ...]]) into [[loc.lineno]]>>=
{ char *temp = line+6;
  <<fail if string [[temp]] contains a non-digit>>
  loc.lineno = atoi(temp);
}
<<fail if string [[temp]] contains a non-digit>>=
{ char *p;
  for (p = temp; *p; p++)
    if (!isdigit(*p))
      errormsg(Error, "non-numeric line number in `@line %s'", temp);
}
<<definitions>>=
void insist(char *line, char *keyword, char *msg) {
  <<if [[line==NULL]] die of premature end of file>>
  if (!is_keyword(line,keyword))
    impossible(msg);
}
<<if [[line==NULL]] die of premature end of file>>=
if (line==NULL) {
    impossible("End of file occurred in mid-module");
}
<<declarations>>=
void insist(char *line, char *keyword, char *msg);
@
\subsection{Simple callback procedure}
We've got a callback to do I/O
<<definitions>>=
typedef struct io {
  FILE *out;
  void (*putline)(void *out, char *line);
} *IO;

static void write_pretty(void *closure, Parttype type, char *contents) {
  IO io = (IO) closure;
  switch(type) {
    case START_OF_CHUNK: break;
    case END_OF_CHUNK:   break;
    case STRING:    	 fprintf(io->out, "@text %s\n",       contents); break;
    case LITERAL:    	 fprintf(io->out, "@literal %s\n",    contents); break;
    case USE_CHUNK:      fprintf(io->out, "@use %s\n",        contents); break;
    case NEWLINE:        io->putline(io->out, "@nl");			 break;
    case DEFINITION:     fprintf(io->out, "@index defn %s\n", contents); break;
    case WHATSIT:   	 io->putline(io->out, contents);		 break;
    default: assert(0);
  }
}
@

\subsection{Sketch for a two-pass driver}
The best plan would be to use a two-pass driver.
On the first pass it would
\begin{itemize}
\item
Read in all lines and builds a def-use tree.
\item
Decide on a prettyprinter for each root, either using the root name
or a suffix (and probably based on info from the command line as well
as defaults).
\item
Propagate info from parents to children.
Inconsistent children (distinct prettyprinters) become new roots.
\end{itemize}
Then on the second pass it could use the propagated info to select a
prettyprinter for each chunk.

\subsection{One-pass driver}
This just uses a single prettyprinter.
This means get and put are just I/O.
<<one-pass definitions>>=
static char *get_stripped(void *in) {
  FILE *fp = (FILE *)in;
  char *line = getline(fp);
  if (line) {
    int i = strlen(line) - 1;
    if (i >= 0 && line[i] == '\n') line[i] = 0;
  }
  return line;
}

static void put_stripped(void *out, char *line) {
  FILE *fp = (FILE *)out;
  fputs(line, fp);
  fputc('\n', fp);
}
@
If we only ever use a single prettyprinter, we make the closure the
I/O closure.
[As a trick, we return no prettyprinter if the chunk name has a blank.
Commented out for testing purposes.]
<<one-pass definitions>>=
static PrettyPrinter make_pp(void *cl, char *name) {
  // if (strchr(name, ' ')) return NULL;
  return new_prettyprinter(write_pretty, cl);
}
@
The program is always a filter, so it uses stdin and stdout.
<<one-pass definitions>>=
main (int argc, char *argv[]) {
  struct io io;
  io.out = stdout;
  io.putline = put_stripped;
  pretty(get_stripped, stdin, put_stripped, stdout, make_pp, &io);
  return 0;
}
@
\subsection{Boilerplate}
<<*>>=
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include "strsave.h"
#include "getline.h"
#include "match.h"
#include "errors.h"
#include "pretty.h"

typedef struct location {       /* identify lines of source */
    char *filename;
    int lineno;
} Location;

<<declarations>>
<<definitions>>
<<one-pass definitions>>

