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This chapter discusses ways to read and write files at various levels---at marks, into regions, and into buffers. This also treats automatic mechanisms that affect the state of buffers in which files are read.
The user specifies file options with a special syntax on the first line of a file. If the first line contains the string "-*-", then Hemlock interprets the text between the first such occurrence and the second, which must be contained in one line , as a list of "option: value" pairs separated by semicolons. The following is a typical example:
;;; -*- Mode: Lisp, Editor; Package: Hemlock -*-
See the Hemlock User's Manual for more details and predefined options.
File type hooks are executed when Hemlock reads a file into a buffer based on the type of the pathname. When the user specifies a Mode file option that turns on a major mode, Hemlock ignores type hooks. This mechanism is mostly used as a simple means for turning on some appropriate default major mode.
This checks for file options in buffer and invokes handlers if there are any. Pathname defaults to buffer's pathname but may be nil. If there is no Mode file option that specifies a major mode, and pathname has a type, then this tries to invoke the appropriate file type hook. read-buffer-file calls this.
There is no good way to uniquely identify buffer names and pathnames. However, Hemlock has one way of mapping pathnames to buffer names that should be used for consistency among customizations and primitives. Independent of this, Hemlock provides a means for consistently generating prompting defaults when asking the user for pathnames.
This returns Buffer Pathname if it is bound. If it is not bound, and buffer's name is composed solely of alphnumeric characters, then return a pathname formed from buffer's name. If buffer's name has other characters in it, then return the value of Last Resort Pathname Defaults Function called on buffer.
Common Lisp pathnames are used by the file primitives. For probing, checking write dates, and so forth, all of the Common Lisp file functions are available.
This function writes the contents of region to the file named by pathname. This writes region using a stream as if it were opened with :if-exists supplied as :rename-and-delete.
When keep-backup, which defaults to the value of Keep Backup Files, is non-nil, this opens the stream as if :if-exists were :rename. If append is non-nil, this writes the file as if it were opened with:if-exists supplied as :append.
This signals an error if both append and keep-backup are supplied as non-nil.
write-buffer-file writes buffer to the file named by pathname including the following:
It assumes pathname is somehow related to buffer's pathname: if the buffer's write date is not the same as pathname's, then this prompts the user for confirmation before overwriting the file.
It consults Add Newline at EOF on Writing File (see Hemlock User's Manual for possible values) and interacts with the user if necessary.
It sets Pathname Defaults, and after using write-file, marks buffer unmodified.
It updates Buffer's pathname and write date.
It renames the buffer according to the new pathname if possible.
It invokes Write File Hook.
Write File Hook is a list of functions that take the newly written buffer as an argument.
read-buffer-file deletes buffer's region and uses read-file to read pathname into it, including the following:
It sets buffer's write date to the file's write date if the file exists; otherwise, it messages that this is a new file and sets buffer's write date to nil.
It moves buffer's point to the beginning.
It sets buffer's unmodified status.
It sets buffer's pathname to the result of probing pathname if the file exists; otherwise, this function sets buffer's pathname to the result of merging pathname with default-directory.
It sets Pathname Defaults to the result of the previous item.
It processes the file options.
It invokes Read File Hook.
Read File Hook is a list functions that take two arguments---the buffer read into and whether the file existed, t if so.
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