Getting user input in Odin CLI apps

I had been doing some basic interpreter work in Go and wanted to redo it in another language to solidify my understanding. Naturally, I chose Odin, it’s another great language, with a Go-like, easy-to-approach syntax and no unnecessary complexity.

I had previously used Odin while building the Jack compiler for my Nand2Tetris projects last year, and I really enjoyed the experience.

As I began reimplementing my interpreter in Odin, I realized I’d never actually dealt with reading interactive user input from the command line. Since I needed a REPL, this was a must. Surprisingly, just like Go’s bufio pattern, it’s not super obvious how to do this in Odin either.

After digging around in the Odin Discord, I found how to do it.

And here is a REPL that echoes your input:

package main

import "core:bufio"
import "core:fmt"
import "core:os"

main :: proc() {

    scanner: bufio.Scanner
    stdin := os.stream_from_handle(os.stdin)
    bufio.scanner_init(&scanner, stdin, context.temp_allocator)

    for {
        fmt.printf("> ")
        if !bufio.scanner_scan(&scanner) {
            break
        }
        line := bufio.scanner_text(&scanner)
        if line == "q" {break}
        fmt.println(line)
    }

    if err := bufio.scanner_error(&scanner); err != nil {
        fmt.eprintln("error scanning input: %v", err)
    }

    free_all(context.temp_allocator)
}