hussar-lang/hussar

package repl

import (
    "bufio"
    "io"

    "github.com/ttacon/chalk"

    "github.com/hussar-lang/hussar/evaluator"
    "github.com/hussar-lang/hussar/lexer"
    "github.com/hussar-lang/hussar/object"
    "github.com/hussar-lang/hussar/parser"
)

const PROMPT = ">> "

func Start(in io.Reader, out io.Writer) {
    scanner := bufio.NewScanner(in)
    env := object.NewEnvironment()
    promptColor := chalk.Cyan.NewStyle().WithTextStyle(chalk.Bold).Style

    for {
        io.WriteString(out, promptColor(PROMPT))
        scanned := scanner.Scan()
        if !scanned {
            return
        }
        line := scanner.Text()
        l := lexer.New(line)
        p := parser.New(l)

        program := p.ParseProgram()
        if len(p.Errors()) != 0 {
            printParserErrors(out, p.Errors())
            continue
        }

        evaluated := evaluator.Eval(program, env)
        if evaluated != nil {
            io.WriteString(out, evaluated.Inspect())
            io.WriteString(out, "\n")
        }
    }
}

func printParserErrors(out io.Writer, errors []string) {
    errColor := chalk.Red.NewStyle().WithTextStyle(chalk.Bold).Style

    io.WriteString(out, errColor("PARSER ERROR!\n"))
    for _, msg := range errors {
        io.WriteString(out, errColor("  [!] ")+msg+"\n")
    }
}