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== Pathnames ==

Pathnames are immutable record-style objects of a disjoint type that represent the natural components of (string) filenames in a way that is intended to be system-independent.  This design is mostly based on MIT Scheme, which is mostly based on Common Lisp.  However, it is extended to accept additional components which are required to represent URIs and IRIs as well as filenames.  In addition, given the pervasiveness of Windows and Posix filenames nowadays, specific provisions for them has been made.

== Components and their accessors ==

The components of a pathname are ''scheme'', ''host'', ''port'', ''username'', ''password'', ''device'', ''directory'', ''name'', ''type'', ''query'', and ''fragment''.  

''Scheme'' is the scheme part of a URI/IRI.  It is a string.

''Username'' is the username associated with a URI/IRI host.  It is a string.

''Password'' is the password associated with a ''username''.  It is a string.

''Host'' is the host part of a URI/IRI.  It is a string.

''Port'' is the port part of a URI/IRI.  It is an exact integer.

''Device'' is a Windows-style device name without a trailing colon.  It is a string, typically but not always a single character.

''Directory'' is a directory path, which is represented as a list.  The first element is always a symbol, which can be `absolute` or `relative` or `unc`, representing absolute, relative, and UNC directory paths respectively.  The root directory is represented by the list `(absolute)`.  A null directory path is represented by the empty list.  The other elements are strings.

''Name'' is a simple file name without the associated file type or extension, if any.  It is a string.

''Type'' is the type or extension of the filename, without any leading period.  It is a string.

''Query'' is the query part of a URI/IRI.  It is a string.

''Fragment'' is the fragment part of an IRI/URI.  It is a string.

All of these components can also be `#f` to indicate that the component is not present.  In particular, a filename or URI ending in `/` or `\` will result in the file and type components being `#f`.

== The path separator parameter ==

`(pathname-syntax [value]`)

This is a (SRFI 39) parameter whose value is either `windows` or `posix`, and is used to define whether parsing and construction of filenames uses Windows or Posix syntax.  It may have other values, but the result is implementation defined.  The initial value is also implementation-defined.

== Basic procedures ==

The procedures `pathname?` and `pathname=?` do what you expect.  Note that two pathnames may be different according to `pathname=?` but still access the same resource.  Host components are compared case-insensitively.

== Accessors ==

There are 11 accessors corresponding to the 11 components of a pathname, which take the form `pathname-*` where `*` is one of the components.

It is an error to mutate anything returned by any of these accessors.

== Constructors and parsers ==

`(make-pathname `''components''`)`

Constructs and returns a pathname.  ''Components'' is an a-list mapping component names to values.  Component names not defined in this specification are allowed, but the results are implementation-specific.  Any component names not appearing in ''components'' are set to `#f`.

The following procedures accept a string and construct and return a pathname corresponding to that string.

`(filename->pathname `''filename''`)`

Constructs and returns a pathname.  ''Filename'' is a string to be converted to a filename.

If `(pathname-syntax)` is `posix`, then ''filename'' is parsed using `/` as the component separator, the directory, name, and type components are potentially populated from it, and the device component is set to `#f`.

If `(pathname-syntax)` is `windows`, then ''filename'' is parsed using both `\` and `/` as component separators, a leading `//` or `\\` results in a directory component beginning with `unc`, and the device, directory, name, and type components are potentially populated from it.

Finally, the scheme component is set to `"file"`, and the username, password, port, query, and fragment components are set to `#f`.

`(uri->pathname `''uri''`)`

Constructs and returns a pathname.  ''Uri'' is a string to be converted to a pathname.  It is parsed according to IRI rules, which are the same as URI rules except that sequences of `%`-hexdigit-hexdigit escapes that represent UTF-8 byte sequences are parsed into characters, provided the requisite characters are supported by the implementation.

The scheme, host, port, username, password, directory, name, type, query, and fragment components are potentially populated from ''uri''.  The device component is set to `#f`.  If the query part of the IRI consists of name-value pairs separated by `&` or `;` and with `=` between the name and the value, then the query component will be an a-list of strings; otherwise, it will just be a string.

== Deconstructors ==

The following procedures accept a pathname and construct and return a string corresponding to that pathname.

`(pathname->filename `''pathname''`)`

Constructs and returns a filename string from ''pathname''.

If `(pathname-syntax)` is `posix`, then the result is constructed using `/` as the component separator from the directory, name, and type components of ''pathname''.

If `(pathname-syntax)` is `windows`, then the result is constructed using `\` as the component separator from the device, directory, name, and type components.

It is an error if the username, password, port, query, and fragment components are not `#f`.  It is an error if the scheme component is not `"file"`.

`(pathname->uri `''pathname''`)`

Constructs and returns a string according to RFC 3986 rules.  In addition to required `%`-escaping, non-ASCII characters are converted to UTF-8 byte sequences and `%`-escaped.

The scheme, host, port, username, password, directory, name, type, query, and fragment components are used to construct the URI.  It is an error if the device component is not `#f`, or if the `car` of the directory component is not `absolute`.

`(pathname->iri `''pathname''`)`

Constructs and returns a string according to RFC 3987 rules.  No escaping of non-ASCII characters is done.

The scheme, host, port, username, password, directory, name, type, query, and fragment components are used to construct the URI.  It is an error if the device component is not `#f`, or if the `car` of the directory component is not `absolute`.

== Other procedures ==

`(merge-pathnames `''pathname1''` `''pathname2''`)`

Constructs and returns a new pathname with the same components as ''pathname1''.  However, if any component of ''pathname1'' is `#f`, the corresponding component of ''pathname2'' is used instead.  The directory component is handled specially; if the ''pathname1'' component begins with `relative`, the rest of it is appended to the ''pathname2'' component.

`(pathname-absolute-filename? `''pathname''`)`

Returns `#t` if ''pathname'' specifies an absolute or UNC filename.  If `(pathname-syntax)` is `windows`, the device component must be specified.

`(pathname-absolute-uri? `''pathname''`)`

Returns `#t` if ''pathname'' specifies an absolute URI (the fragment component must be #f).

`(pathname-uri? `''pathname''`)`

Returns `#t` if ''pathname'' specifies a URI/IRI (that is, an absolute URI with a possible fragment).

`(pathname-query->alist `''pathname''`)`

Returns the query component of ''pathname'' as an a-list, where `&` and `;` separate the entries in the alist, and `=` separates the `car` from the `cdr`.

`(pathname-directory->string `''pathname''`)`

Returns the directory component of ''pathname'' as a string.  The result consists of the strings in the ''cdr'' of the directory component joined using the path separator, with the separator prepended if the ''car'' is `absolute`.  If `(pathname-syntax)` is `posix`, the path separator is `/`; if `(pathname-syntax)` is `windows`, the path separator is `\`.

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2011-01-14 01:39:14