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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)`, and a null directory path is represented by the list `(relative)`.  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`.

== 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 (as symbols) 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`.

ISSUE: Should `make-pathname` accept multiple arguments rather than a single argument which is an a-list?  Variable a-lists can be constructed by quasiquotation.

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

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

Constructs and returns a pathname.  ''Filename'' is a string representing a Posix filename.

''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`.

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

`(posix-dirname->pathname `''dirname''`)`

Constructs and returns a pathname.  ''Dirname'' is a string representing a Posix directory name.

''Filename'' is parsed using `/` as the component separator.  The directory component is potentially populated from it.

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

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

Constructs and returns a pathname.  ''Filename'' is a string representing a Windows filename.

''Filename'' is parsed using both `\` and `/` as component separators, and a leading `//` or `\\` results in a directory component whose ''car'' is `unc`.  The device and directory, name, and type components are potentially populated from it.

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

`(windows-dirname->pathname `''dirname''`)`

Constructs and returns a pathname.  ''Dirname'' is a string representing a Windows directory name.

''Filename'' is parsed using both `\` and `/` as component separators, and a leading `//` or `\\` results in a directory component whose ''car'' is `unc`.  The device and directory components are potentially populated from it.

The scheme component is set to `"file"`, and the username, password, port, name, type, 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 device component is set to `#f`.  All the other components are potentially populated from ''uri''.

== Deconstructors ==

The following procedures accept a pathname and construct and return a string corresponding to that pathname according to some appropriate convention.

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

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

The result is constructed using `/` as the component separator from the directory, name, and type components of ''pathname''.

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"` or `#f`.

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

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

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"` or `#f`.

`(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 IRI.  It is an error if the device component is not `#f`, or if the first element of the directory component is not `absolute`.

`(pathname-directory->posix-dirname `''pathname''`)`

Returns ''pathname'' as a Posix directory string.  The result consists of the strings in the ''cdr'' of the directory component joined using `/` with another `/` prepended if the ''car'' is `absolute`.

`(pathname-directory->windows-dirname `''pathname''`)`

Returns the ''pathname'' as a Windows directory string.  The result consists of the strings in the ''cdr'' of the directory component joined using `\`, prefixed by one of the following:

 * `\` if the ''car'' of the directory component is `absolute`

 * `\\` followed by the host component followed by `\` if the ''car'' of the directory component is `unc`

 * the device followed by `:` if the device component is not `#f`

 * the empty string otherwise

`(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`.

== Other procedures ==

`(pathname? ''object''`)`

Returns `#t` if ''object'' is a pathname, and `#f` otherwise.

`(pathname=?` ''pathname1''` `''pathname2''`)`

Compares ''pathname1'' and ''pathname2'' for equality, component-wise.  Note that two pathnames may be different according to `pathname=?` but still access the same resource.  The host components are compared case-insensitively.

`(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.

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

Returns `#t` if ''pathname'' specifies an absolute URI/IRI (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`.



    
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2014-08-04 07:05:38

    
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10