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--- playground:plan9_tutorial_sam [2021/04/19 18:17] – adding docu links dsp
+++ playground:plan9_tutorial_sam [2021/04/20 04:59] (current) – adding external command section dsp
@@ Line 63: / Line 63: @@
 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 ===
@@ Line 72: / Line 133: @@
     * 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 ===