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--- playground:plan9_tutorial_sam [2021/04/19 21:30] – adding a toy example for regex dsp
+++ playground:plan9_tutorial_sam [2021/04/20 04:59] (current) – adding external command section dsp
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+==== An SDF sam tutorial ====
+===Basic Editing===
+When you run sam newfile you only see the command window (blue area) on top
+but the actual file contents window has not opened.
+Right click on the white area and you will see the filename listed.
+Selecting it and noticing that the cursor changed you can then click and the contents
+will appear. If the file didn't exist there will be no contents.
+After that you can start typing on the text edit window. With your mouse
+you can either select the text edit window or the command window using
+the left mouse button. In the following document commands will appear in bold font.
+The most basic commands to interact with the editor are **q** to quit,
+**w [filename]** to write the file to disk and **u [times]** to undo.
+If we have currently selected a filename and issue the **w** command sam will
+tell us the total amount of characters it wrote. It also might warn us
+if the file does not end with a newline.
+By issuing the **n** command we see the file menu list.
+when the text window has changes of a file
+that haven't been written yet to disk the file line
+in the menu list starts with the ' character.
+To quote //The text editor sam// paper by Rob Pike a file consists of
+   * it's contents, which are an array of characters
+   * the name of the associated disk file
+   * the modified bit that states whether the contents match those of the disk file
+   * a substring of the contents called the "current text" or "dot".
+     * the value of dot is the location of the current text
+     * the contents of dot are the character it contains
+Since edit operations apply on selections we must learn ways to control the value of dot.
+The easiest way is to highlight some text. This action sets dot to that range.
+By the command **p** we print the contents of dot and by the command **=** we see the range
+on the file it maps to.
+By issuing ranges on the editor we will see the text they specify getting highlighted.
+Some example ranges would be
+^Range  ^Decription ^
+|0,$    |from line zero till the end of the file which can also be expressed as ,|
+|3      |the third line|
+|#30,#50|character 30 till character 50|
+|2,#100 |line 2 till character 100|
+To operate on text in or around dot we can use commands like append, change, insert etc.
+For example to delete the text in dot we just press **d** , and to insert sometext before dot
+we would issue **i/sometext/** , or to append it after dot **a/sometext/** . **m** followed by an
+address moves the text in dot after that address. **t** followed by an address just copies
+the text to that address without deleting from the original location.
+=== Editing more than one file ===
+By right clicking and selecting new we can create a new text editing window to work
+on another file. If we have more than one files open we notice that in the file menu
+list we see more lines. The file we are currently working on is marked by a .
+symbol.
+By issuing the **b** command we can set our current file to other files. For example if we have
+files open, named file1 and file2 and we issue b file2 and then n we see that
+file2 will be selected. If we try to open a completely new file that isn't in the
+file menu list, the **b** command will fail. That is why the **B** command exists which
+can be used to create a new entry. Note that if the file didn't exist in the disk
+a write still needs to happen for it's data to be persisted.
+Other basic file menu commands are **D** (to delete an entry) **f** (to rename a file entry)
+**e** (to replace current with file) and **r** (replace dot by the contents of file). Here we
+notice that if we rename an entry that doesn't rename the file on disk. Instead if we
+issue **w** on the renamed entry it will create a new file on disk.
+=== Examples for sam regex ===
+The benefit of sam is that it allows for regex tasks to be chained and also debugged
+easily from within the editor. We will consider a toy example to indent properly some
+code of the form
+<code>
+    if foo {
+     bar
+    }
+</code>
+We would like bar to be indented at 8 spaces in, one more level than //if// is.
+We can start with a regex to detect the opening brace
+<code> , x/{$/ </code>
+should detect, in the whole file (,) these braces.
+Now we can match backwards to find the prepending white space in that line we matched
+by just chaining the next regex.
+<code> , x/{$/ -/^[    ]*/ </code>
+now that matches the white space before.
+We would like to add at least as much white space to the line below and
+then some (4 spaces for example).
+But for that to work the line below must be free of leading white space.
+Therefore we will remove it from any line that is below an opening brace. The search is
+<code>, x/{\n[ ]*/</code>
+and to remove the white space between the start of line and the first character we chain it like
+<code> , x/{\n[ ]*/ s/^[ ]*/    / </code>
+The final form of our regex chain is
+<code>
+, x/{\n[ ]*/ s/^[ ]*/    /
+, x/{$/ -/^[ 	]*/ t .+0
+</code>
+=== Interacting with external commands ===
+Of course creating a indentation program with just regexp would be duplication of work.
+For most languages pretty printers exist like gofmt and cb (C beautifier) let' try
+to run cb on some ugly-fied C.
+<code>
+if  (foo <bar(bz)) {
+	  do(bxm,as);
+wrong;
+   }
+</code>
+To pass all this code through cb we can just select it and then
+issue the command |cb . that would replace the dot by
+<code>
+if  (foo <bar(bz)) {
+	do(bxm,as);
+	wrong;
+}
+</code>
+similarly we can read input from a command
+using < and write to a command using > if we want to count all the
+characters in a selection for example we can highlight it and issue >wc
+, observe that this doesn't changes our current text
+We could also imagine a command where it replaces every
+occurrence of //{DATE}// with the current system date in the whole document
+<code>
+, x/{DATE}/ <date
+</code>
+would find any occurrence of the string //{DATE}// and then replace that
+dot with the output of the date command.
+=== Self guided discoveries ===
+    * create two files (file1 and file2) add text to both, use **n** and **b** to control which file has the focus.
+    * on file2 for example issue continuously<code>
+   r file2
+</code> and repeat. What is happening? why? what if we only issue **r file2** without the 0 afterwards?
+    * can you specify a reverse range like #10,#5 ?
+    * highlight a word. then issue **m+0**. why is this happening? what is **t+0** doing? what if you keep issuing **t+0**?
+    * Improve the toy indent example by
+      * making lines align when no opening brace is detected in the end of line
+      * remove 4 leading spaces if the line has a closing brace
+=== Documentation and more ===
+    *[[http://man.cat-v.org/9front/1/sam|man sam(1)]]
+    *[[http://doc.cat-v.org/plan_9/4th_edition/papers/sam/|The Text Editor Sam (Rob Pike)]]
+    *[[http://doc.cat-v.org/bell_labs/sam_lang_tutorial/sam_tut.pdf|A Tutorial For The Sam Command Language (Rob Pike)]]
+    *[[http://sam.cat-v.org/cheatsheet/sam-refcard.pdf|Sam Cheatsheet (PDF) (Steve Simon)]]
+    *[[https://www.youtube.com/watch?v=JbWdS7isUiI|A Sam Session youtube video (Pilgon Sesh60)]]
+    *[[https://plan9docs.wordpress.com/2012/05/07/using-the-sam-editor/|Using The Sam Editor from plan9docs (iainws)]]