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I attempted to use penlight's pl.pretty.dump() for a quick and
dirty document format for a simple utility. Its one-argument form
where the first parameter is the table to dump to stdout works
exactly as documented. Its two-argument form where the second
argument is the name of a file fails with a mysterious error:

Lua 5.1.4  Copyright (C) 1994-2008, PUC-Rio
> require 'pl.pretty'
> pl.pretty.dump({}, "test.txt")
utils.assert_string: argument 2 expected a 'string', got a 'table'
stack traceback:
        stdin:1: in main chunk
        [C]: ?


Note that the message appears to blame argument 2 of my call to
pl.pretty.dump() for being a table, but it is obviously not a
table. The issue is that the implementation of dump() leverages
pl.util.writefile(), but doesn't pass the table through
pl.pretty.write() to make it into a pretty string first. This is
confounded by the (otherwise rational) decision to make all stack
traces start from the user's call site.

At line 160 of pl/pretty.lua, change:
-        return utils.raise(utils.writefile((select(1,...)),t))
+ return utils.raise(utils.writefile((select(1,...)),write(t)))

Incidentally, as packaged in Lua for Windows, the penlight
documentation has broken links.... probably because the
docs\penlight\index.html assumes that the folder api\modules is
just modules. Also, docs\penlight\function_index.html has good
links, but leaves out the pl.pretty module.

Ross Berteig                     
Cheshire Engineering Corp.