Update README.md

Author: bachish

src/main/kotlin/org/srcgll/grammar/combinator/README.md

@@ -1,32 +1,99 @@
-## Declaration:
-for nonterminals
+# Grammar combinator 
+Kotlin DSL for describing context-free grammars.
+
+
+
+## Declaration
+
+Example for A* grammar
+
+*EBNF*
+```
+A = "a"
+S = A* 
+```
+*DSL*
+```kotlin
+class AStar : Grammar() {
+        var A = Term("a")
+        var S by NT()
+
+        init {
+            setStart(S)
+            S = Many(A)
+        }
+    }
+```
+### Non-terminals
 
 `val S by NT()`
 
-for terminals 
+Non-terminals must be fields of the grammar class. Be sure to declare using delegation `by NT()`!!!
+
+Start non-terminal set with method `setStart(nt)`. Can be set once for grammar.
+
+### Terminals 
 
 `val A = Term("a")`
-## Operation:
+
+`val B = Term(42)`
+
+Terminal is a generic class. Can store terminals of any type. Terminals are compared based on their content. 
+
+They can be declared as fields of a grammar class or directly in productions.
+
+## Operations
+Example for Dyck language
+
+*EBNF*
+```
+S = S1 | S2 | S3 | ϵ
+S1 = '(' S ')' S 
+S2 = '[' S ']' S 
+S3 = '{' S '}' S 
+```
+*DSL*
+```kotlin
+class DyckGrammar : Grammar() {
+        var S by NT()
+        var S1 by NT()
+        var S2 by NT()
+        var S3 by NT()
+
+        init {
+            setStart(S)
+            S = S1 or S2 or S3 or Epsilon
+            S1 = Term("(") * S * Term(")") * S
+            S2 = Term("[") * S * Term("]") * S
+            S3 = Term("{") * S * Term("}") * S
+        }
+    }
+```
+### Production
+A → B = A = B
 
 ### Concatenation
 (.): Σ∗ × Σ∗ → Σ∗
 
 a . b = a * b
 
+### Alternative
+a | b = a or b
+
 ### Kleene Star
 $a* = U_{i=0}^{\inf}a^i$
 
 a* = Many(a)
 
-`todo a += Some(a)`
-
-### Alternative 
-a | b = a or b
-
-### Production
-A → B = A = B
+`todo: a+ = some(a)`
 
 ### Optional 
 a? -> a | Epsilon
 
-`todo a? = opt(a)`
+Epsilon -- constant terminal with behavior corresponding to the $\epsilon$ terminal (empty string).
+
+`todo: a? = opt(a)`
+
+## RSM 
+DSL allows to get the RSM corresponding to the grammar using the `getRsm` method.
+The algorithm of RSM construction is based on Brzozowski derivations.