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% -*- mode: Noweb; noweb-code-mode: icon-mode -*-
\section{Getting chunks from an external ``dictionary''}
Mike Smith wants to do an unweblike thing: keep his code and
documentation in separate source files.
I~think he wants to do this so he can enable the \emph{same} code
chunks to appear in \emph{multiple} documents, with guaranteed
consistency, but I~suppose the reasons don't matter.
In any case, he wants syntax for referring to a code chunk from an
external database, and for displaying the definition(s) of that chunk
exactly where he specifies.
I~suggested solving the problem with a Noweb filter.
He can refer to chunks using the approved source syntax:
\texttt{[{}[<{}<}\emph{chunk name}\texttt{>{}>]{}]}.
To pull in the definitions from the external database, I suggested he
provide an empty definition.
Since such a definition can be written in one line (two lines if the
definition is followed by a documentation chunk), he can pull in many
definitions concisely.
This program is the noweb filter that does the job.
Named ``\texttt{xchunks},'' short for ``external chunks,'' it pulls in
definitions from an external database.
The external database is itself simply a list of Noweb files.
It's a bit more liberal than defined above; a chunk is considered
empty if its definition contains at most whitespace.
A late-breaking bug: we need to resynchronize line numbers.
<<*>>=
record chunk(lines, type)
# lines is all the lines of the chunk
# type is "code" or "docs" or "unknown"
procedure main(args)
local merge, summary
while args[1][1] == "-" do
case args[1] of {
"-merge" : merge := get(args)
"-summary" : { get(args); summary := " (summary)" }
default : break
}
*args > 0 | stop("xchunks needs an external database")
<<let [[db]] be an open file giving the database pipeline from [[args]]>>
dbchunks := readchunks(db)
defns := defnstable(dbchunks)
# defns maps name to list of code chunks defining that name
if \merge then
every merge_chunks(!defns)
if \summary then
every add_defn_string(!defns, summary)
thisdoc := readchunks(&input)
every c := !thisdoc do
if c.type ~== "code" | notEmpty(c) | /defns[chunkName(c)] then
every write(!c.lines)
else {
write("@crc_prefix on")
every write(!(!defns[chunkName(c)]).lines)
write("@crc_prefix off")
}
end
@
Reading chunks is fairly straightforward; we look for begin and end.
The loop logic is a little less pleasant than I would like.
<<*>>=
procedure readchunks(infile)
local chunks, c
local file, lnum, lines, startline
chunks := []
lnum := 1
while line := read(infile) do
line ?
if ="@file " then {
file := tab(0)
lnum := 1
} else if ="@line " then {
lnum := integer(tab(0))
} else if ="@begin " then {
lines := []
put(lines, "@file " || \file)
put(lines, "@line " || lnum)
put(lines, line)
startline := line
c := chunk(lines, tab(upto(' ')|0))
line := read(infile) | stop("unmatched ", startline)
while line ? not ="@end " do {
put(c.lines, line)
line := read(infile) | stop("unmatched ", startline)
line ?
if ="@file " then { file := tab(0); lnum := 1 }
else if ="@line " then { lnum := integer(tab(0)) }
else if =("@nl"|"@index nl") & pos(0) then { lnum := lnum + 1 }
}
put(c.lines, line)
put(chunks, c)
} else {
put(chunks, chunk([line], "unknown"))
line ?
if ="@file " then { file := tab(0); lnum := 1 }
else if ="@line " then { lnum := integer(tab(0)) }
else if =("@nl"|"@index nl") & pos(0) then { lnum := lnum + 1 }
}
return chunks
end
@
Building the definitions table is easy.
<<*>>=
procedure defnstable(chunks)
t := table()
every c := !chunks & c.type == "code" do {
/t[chunkName(c)] := []
put(t[chunkName(c)], c)
}
return t
end
@
The basic functions [[chunkName]] and [[notEmpty]] require search.
You could imagine caching these, but since they're called twice and at
most once per chunk, respectively, I doubt it's worth it.
<<*>>=
procedure chunkName(c)
return (!c.lines ? (="@defn " & tab(0))) | stop("no @defn in code chunk")
end
procedure notEmpty(c)
static nonwhite
initial nonwhite := ~' \t'
return !c.lines ? ="@use " | (="@text ", upto(nonwhite))
end
@
Finally, here's how we get the database.
<<let [[db]] be an open file giving the database pipeline from [[args]]>>=
db := "markup"
every db ||:= " " || !args
db := open(db, "rp") | stop("cannot pipe from ", image(db))
@
To merge adjacent definitions, we strip leading and trailing markup.
<<*>>=
procedure merge_chunks(chunks)
while *chunks > 1 do {
c := get(chunks)
strip_code_tail(c)
strip_code_head(chunks[1])
every put(c.lines, !chunks[1].lines)
chunks[1] := c
}
return chunks
end
@
<<*>>=
procedure strip_code_tail(c)
if c.lines[-1] ? match("@end code") then
pull(c.lines)
else
stop("Unexpected line")
return c
end
procedure strip_code_head(c)
local pfx
pfx := []
if match("@begin code", c.lines[1]) then
get(c.lines)
else
stop("bad line " || c.lines[1])
while not match("@defn ", c.lines[1]) do
push(pfx, get(c.lines))
get(c.lines) | stop("this can't happen")
while c.lines[1] ~== "@nl" do
push(pfx, get(c.lines))
get(c.lines) | stop("this can't happen")
every push(c.lines, !pfx)
return c
end
@
<<*>>=
procedure add_defn_string(chunks, s)
every c := !chunks & i := 1 to *c.lines do
if match("@defn ", c.lines[i]) then
c.lines[i] ||:= s
return chunks
end
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