As of 1.8, 'go tool yacc' is no longer included. Instead, obtain 'goyacc' with the following:
go get -u golang.org/x/tools/cmd/goyacc
Followed by:
goyacc -o calc.go -p Calc calc.y
References:
https://github.com/golang-samples/yacc/tree/master/simple
https://godoc.org/github.com/cznic/goyacc
https://blog.golang.org/generate (outdated)
