Add syntax help menu and cli option

parse.lisp

@@ -86,6 +86,77 @@ proposition."))
     (iff "<->" "<>" "<=>" "⇔" "↔" "≡" "iff" "=" "==" "xnor" "⊙"))
   "Alist table of operator symbols and their possible string representations.")
 
+(defparameter *operator-descriptions* ;; noindent 30
+  `((open-paren ("open parenthesis")
+     ,(format nil "Used in combination with a close parenthesis to denote ~
+some terms to be evaluated before the surrounding terms.")
+     (((and (or true true) false) . false)
+      ((or true (and true false)) . true)))
+    (close-paren ("close parenthesis")
+     "Used to close a group started with an open parenthesis."
+     ()) ;; no examples for closed paren
+    (and ("and" "conjunction")
+     ,(format nil "Evaluate to true only if the expressions to the left and ~
+right evaluate to true.")
+     (((and true true) . true)
+      ((and true false) . false)))
+    (nand ("nand" "non-conjunction")
+     ,(format nil "Evaluate to true unless the expressions to the left and ~
+right are both true. This is the negation of the 'and' operator.")
+     (((nand true true) . false)
+      ((nand true false) . true)
+      ((nand false false) . true)))
+    (or ("or" "disjunction")
+     ,(format nil "Evaluate to true if the expression to the left is true, the ~
+expression to the right is true, or both the left and right expressions are ~
+true.")
+     (((or true true) . true)
+      ((or true false) . true)
+      ((or false false) . false)))
+    (nor ("nor" "non-disjunction")
+     ,(format nil "Evaluate to true if the expressions to the left and right ~
+are both false. This is the negation of the 'or' operator.")
+     (((nor true true) . false)
+      ((nor true false) . false)
+      ((nor false false) . true)))
+    (xor ("exclusive or" "exclusive disjunction") ;; noindent 30
+     ,(format nil "Evaluate to true if the expression to the left is true or ~
+if the expression to the right is true, but not if both of them are true.")
+     (((xor true true) . false)
+      ((xor true false) . true)))
+    (not ("not" "negation")
+     ,(format nil "Evaluate to false if the expression to the left evaluates ~
+to true, and evaluate to true if the expression to the left evaluates to ~
+false. This is a unary operator (it only applies to the expression following ~
+it).")
+     (((not true) . false)
+      ((not false) . true)))
+    (implies ("implies" "conditional")
+     ,(format nil "Evaluate to false if the expression to the left evaluates ~
+to true and the expressions to the right evaluates to false. Otherwise, ~
+evaluate to true.")
+     (((implies true true) . true)
+      ((implies true false) . false)
+      ((implies false true) . true)
+      ((implies false false) . true)))
+    (converse ("converse")
+     ,(format nil "Evaluate to false if the expression to the right evaluates ~
+to true and the expression to the left evaluates to false. Otherwise, evaluate ~
+to true. This is the 'implies' operator with its arguments flipped.")
+     (((implies true true) . true)
+      ((implies true false) . true)
+      ((implies false true) . false)
+      ((implies false false) . true)))
+    (iff ("biconditional" "equivalent")
+     ,(format nil "Evaluate to true if the expressions to the left and rigt ~
+evaluate to the same value. That is, they are both true or both false.")
+     (((iff true true) . true)
+      ((iff true false) . false)
+      ((iff false false) . true))))
+  "Alist table of operator symbols and their descriptions. The format of this
+list is SYMBOL NAMES DESCRIPTION (&rest (EXAMPLE LEFT . EXAMPLE RIGHT)). These
+are useful for use in things like syntax explanation messages.")
+
 (defun operator-symbol (oper-str)
   "Return the symbol for OPER-STR, or nil if it is not a know operator."
   (loop for (oper-sym . strs) in *operator-symbol-table*