add mod and exp functions, tests, and also some snippets for common

patterns in the readme

Readme.org

@@ -37,17 +37,67 @@ https://matrix.to/#/#vomitorium:matrix.sunnypup.io
 **** TODO Anatomy
 **** TODO Naming conventions
 **** TODO Undefining variables and functions
-*** TODO Easy patterns
-**** TODO while-let combo
-**** TODO main loop application
-**** TODO let destructuring
-**** TODO if-set?
-*** TODO Builtin functions
-*** TODO Documentation
-**** TODO Tests
-**** TODO Help function
-**** TODO Env function
-**** TODO Snippets directory
+** Easy patterns
+This section can serve as a sort of cookbook for a user who is new to leveraging LISP languages or unsure of where to start with ~relish~.
+More ideas may be explored in the file:snippets directory of this project.
+The author encourages any users to contribute their own personal favorites not already in this section either by adding them to the file:snippets folder, or to extend the documentation here.
+*** while-let combo
+#+BEGIN_SRC lisp
+          ;;  myiter = (1 (2 3 4 5 6))
+          (def myiter 'iterator over a list' (head (1 2 3 4 5 6)))
+
+          ;; iterate over each element in mylist
+          (while (gt? (len (cdr myiter)) 0) ;; while there are more elements to consume
+            (let ((elem (car myiter)) ;; elem = consumed element from myiter
+                  (remaining (cdr myiter))) ;; remaining = rest of elements
+              (echo elem) ;; do a thing with the element, could be any operation
+              (def myiter (head remaining)))) ;; consume next element, loop
+#+END_SRC
+
+The while-let pattern can be used for many purposes. Above it is used to iterate over elements in a list. It can also be used to receive connections to a socket and write data to them.
+*** TODO main loop application
+- state switch (while-toggle)
+- state calculation
+*** TODO short-circuit guard
+- circuit example
+- while-not-circuit-do-more-work
+*** let destructuring
+~let~ is very useful for destructuring complex return types. If you have a function that may return a whole list of values you can then call it from ~let~ to consume the result data.
+In this example a let form is used to destructure a call to ~head~. ~head~ returns a list consisting of ~(first-element rest-of-list)~ (for more information see ~(help head)~).
+The ~let~ form starts with the output of ~head~ stored in ~head-struct~ (short for head-structured). The next variables defined are ~first~ and ~rest~ which contain individual elements from the return of the call to ~head~.
+Finally, the bodies evaluated in the ~let~ form are able to operate on the head and the rest.
+  #+BEGIN_SRC lisp
+    ;; individually access the top of a list
+    (let ((head-struct (head (1 2 3))
+        (first (car head-struct))
+        (rest (cdr head-struct)))
+       (echo "this is 1: " first)
+       (echo "this is 2, 3: " rest))
+  #+END_SRC
+*** if-set?
+One common pattern seen in bash scripts and makefiles is the set-variable-if-not-set pattern.
+#+BEGIN_SRC shell
+  MYVAR ?= MY_SPECIAL_VALUE
+#+END_SRC
+Translated, can be seen below 
+#+BEGIN_SRC lisp
+    (if (set? myvar)
+        () ;; no need to do anything... or add a call here
+        (def myvar "MY_SPECIAL_VALUE"))
+#+END_SRC
+
+Alternatively this combination can be used to process flags in a script or application:
+#+BEGIN_SRC lisp
+  (if (set? myflag)
+      (process-flag myflag)
+      ())
+#+END_SRC
+** TODO Builtin functions
+*** TODO Env function
+** TODO Documentation
+*** TODO Tests
+*** TODO Help function
+*** TODO Snippets directory
 
 ** Configuration
 By default Relish will read from ~/.relishrc for configuration, but the default shell will also accept a filename from the RELISH_CFG_FILE environment variable.
@@ -158,8 +208,8 @@ Will need a concatenate function for tables
 **** DONE sub
 **** DONE div
 **** DONE mul
-**** TODO exp
-**** TODO mod
+**** DONE exp
+**** DONE mod
 ***** TODO Test for Let Destructuring
 **** TODO inc
 **** TODO dec