Unix-y pipelines in Go (functional programming)

pipeline.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"runtime"
	"strings"
)

func main() {
	Run(Cat("testfile.txt"), Grep("model"), Stdout())
}

type Comms struct {
	Tx chan<- string
	Rx <-chan string
}

func Run(comms ...Comms) {
	for i := 0; i < len(comms); i++ {
		if i+1 < len(comms) {
			go func(inComm, outComm Comms) {
				defer close(outComm.Tx)
				for line := range inComm.Rx {
					outComm.Tx <- line
				}
			}(comms[i], comms[i+1])
		} else {
			for _ = range comms[i].Rx {
			}
		}
	}
}

func Cat(filename string) Comms {
	file, err := os.Open(filename)
	if err != nil {
		log.Fatal(err)
	}
	out := make(chan string)

	go func() {
		defer func() {
			file.Close()
			close(out)
		}()

		scanner := bufio.NewScanner(file)
		for scanner.Scan() {
			out <- scanner.Text()
		}

		if err := scanner.Err(); err != nil {
			log.Fatal(err)
		}
	}()

	return Comms{nil, out}
}

func Grep(grep string) Comms {
	in := make(chan string)
	out := make(chan string)

	go func() {
		defer close(out)
		for line := range in {
			if strings.Contains(line, grep) {
				out <- line
			}
		}
	}()

	return Comms{in, out}
}

func Stdout() Comms {
	in := make(chan string)
	out := make(chan string)

	go func() {
		defer close(out)
		for line := range in {
			fmt.Println(line)
		}
	}()

	return Comms{in, out}
}