Create task4

submission/paah/task4

@@ -0,0 +1,61 @@
+package main
+
+import (
+  "fmt"
+  "os"
+)
+
+type Group struct {
+  Expression *Expression `'(' @@ ')'`
+}
+
+type Option struct {
+  Expression *Expression `'[' @@ ']'`
+}
+
+type Repetition struct {
+  Expression *Expression `'{' @@ '}'`
+}
+
+type Literal struct {
+  Start string `@String`
+  End   string `[ '…' @String ]`
+}
+
+type Term struct {
+  Name       string      `@Ident |`
+  Literal    *Literal    `@@ |`
+  Group      *Group      `@@ |`
+  Option     *Option     `@@ |`
+  Repetition *Repetition `@@`
+}
+
+type Sequence struct {
+  Terms []*Term `@@ { @@ }`
+}
+
+type Expression struct {
+  Alternatives []*Sequence `@@ { '|' @@ }`
+}
+
+type Expressions []*Expression
+
+type Production struct {
+  Name        string      `@Ident '='`
+  Expressions Expressions `@@ { @@ } '.'`
+}
+
+type EBNF struct {
+  Productions []*Production `{ @@ }`
+}
+
+func main() {
+  parser, err := participle.Build(&EBNF{}, nil)
+  if err != nil { panic(err) }
+
+  ebnf := &EBNF{}
+  err = parser.Parse(os.Stdin, ebnf)
+  if err != nil { panic(err) }
+
+  json.NewEncoder(os.Stdout).Encode(ebnf)
+}