Operand =
  Ident | BasicLit |
  ParenExpr |
  FuncType | FuncLit |
  CompositeLit | ComprehensionExpr |
  ArrayType | SliceLit |
  StructType | PointerType | InterfaceType | MapType | ChanType

ParenExpr =
  '(' Expr ')'

PrimaryExpr = 
  Operand *primaryExprSuffix

primaryExprSuffix =
  selectorExprSuffix | typeAssertExprSuffix |
  sliceExprSuffix | indexExprSuffix |
  callExprSuffix | commandExprSuffix |
  compositeLitSuffix |
  errWrapExprSuffix

selectorExprSuffix = '.' Ident
typeAssertExprSuffix = '.' '(' Type ')'
sliceExprSuffix = '[' ... ']'
indexExprSuffix = '[' ... ']'
callExprSuffix = '(' Args ')' 
commandExprSuffix = Args
compositeLitSuffix = '{' Elements '}'
errWrapExprSuffix = '!' | '?'

ErrWrapExpr =
  PrimaryExpr ?("?:" UnaryExpr)

UnaryExpr =
  ('+' | '-' | '!' | '^' | '&' | "<-") UnaryExpr |
  StarExpr |
  ErrWrapExpr

StarExpr = '*' UnaryExpr

BinaryExpr =
  UnaryExpr BinaryOp BinaryExpr

RangeExpr =
  ?BinaryExpr ':' BinaryExpr ?(':' BinaryExpr)

LambdaExpr =
  ?(Ident | tupleExpr) "=>" lambdaExprBody

tupleExpr =
  '(' Idents ')'

lambdaExprBody =
  '(' Exprs ')' |
  '{' ... '}' |
  Expr

Expr =
  BinaryExpr | RangeExpr | LambdaExpr