func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
	switch x := x.(type) {
	default:
		buf.WriteString("(bad expr)")  
	case *ast.Ident:
		buf.WriteString(x.Name)
	case *ast.Ellipsis:
		buf.WriteString("...")
		if x.Elt != nil {
			WriteExpr(buf, x.Elt)
		}
	case *ast.BasicLit:
		buf.WriteString(x.Value)
	case *ast.FuncLit:
		buf.WriteByte('(')
		WriteExpr(buf, x.Type)
		buf.WriteString(" literal)")  
	case *ast.CompositeLit:
		buf.WriteByte('(')
		WriteExpr(buf, x.Type)
		buf.WriteString(" literal)")  
	case *ast.ParenExpr:
		buf.WriteByte('(')
		WriteExpr(buf, x.X)
		buf.WriteByte(')')
	case *ast.SelectorExpr:
		WriteExpr(buf, x.X)
		buf.WriteByte('.')
		buf.WriteString(x.Sel.Name)
	case *ast.IndexExpr:
		WriteExpr(buf, x.X)
		buf.WriteByte('[')
		WriteExpr(buf, x.Index)
		buf.WriteByte(']')
	case *ast.SliceExpr:
		WriteExpr(buf, x.X)
		buf.WriteByte('[')
		if x.Low != nil {
			WriteExpr(buf, x.Low)
		}
		buf.WriteByte(':')
		if x.High != nil {
			WriteExpr(buf, x.High)
		}
		if x.Slice3 {
			buf.WriteByte(':')
			if x.Max != nil {
				WriteExpr(buf, x.Max)
			}
		}
		buf.WriteByte(']')
	case *ast.TypeAssertExpr:
		WriteExpr(buf, x.X)
		buf.WriteString(".(")
		WriteExpr(buf, x.Type)
		buf.WriteByte(')')
	case *ast.CallExpr:
		WriteExpr(buf, x.Fun)
		buf.WriteByte('(')
		for i, arg := range x.Args {
			if i > 0 {
				buf.WriteString(", ")
			}
			WriteExpr(buf, arg)
		}
		if x.Ellipsis.IsValid() {
			buf.WriteString("...")
		}
		buf.WriteByte(')')
	case *ast.StarExpr:
		buf.WriteByte('*')
		WriteExpr(buf, x.X)
	case *ast.UnaryExpr:
		buf.WriteString(x.Op.String())
		WriteExpr(buf, x.X)
	case *ast.BinaryExpr:
		WriteExpr(buf, x.X)
		buf.WriteByte(' ')
		buf.WriteString(x.Op.String())
		buf.WriteByte(' ')
		WriteExpr(buf, x.Y)
	case *ast.ArrayType:
		buf.WriteByte('[')
		if x.Len != nil {
			WriteExpr(buf, x.Len)
		}
		buf.WriteByte(']')
		WriteExpr(buf, x.Elt)
	case *ast.StructType:
		buf.WriteString("struct{")
		writeFieldList(buf, x.Fields, "; ", false)
		buf.WriteByte('}')
	case *ast.FuncType:
		buf.WriteString("func")
		writeSigExpr(buf, x)
	case *ast.InterfaceType:
		buf.WriteString("interface{")
		writeFieldList(buf, x.Methods, "; ", true)
		buf.WriteByte('}')
	case *ast.MapType:
		buf.WriteString("map[")
		WriteExpr(buf, x.Key)
		buf.WriteByte(']')
		WriteExpr(buf, x.Value)
	case *ast.ChanType:
		var s string
		switch x.Dir {
		case ast.SEND:
			s = "chan<- "
		case ast.RECV:
			s = "<-chan "
		default:
			s = "chan "
		}
		buf.WriteString(s)
		WriteExpr(buf, x.Value)
	}
}
WriteExpr writes the (possibly shortened) string representation for x to buf.
Shortened representations are suitable for user interfaces but may not
necessarily follow Go syntax.
package types
import (
	"bytes"
	"github.com/faiface/generics/go/ast"
)
func ExprString(x ast.Expr) string {
	var buf bytes.Buffer
	WriteExpr(&buf, x)
	return buf.String()
}