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repl.go
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repl.go
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package repl
import (
"bufio"
"fmt"
"github.com/digital-codex/monkey/evaluator"
"github.com/digital-codex/monkey/object"
"github.com/digital-codex/monkey/parser"
"io"
"log"
"os/user"
)
const MONKEY = `
__,__
.--. .-" "-. .--.
/ .. \/ .-. .-. \/ .. \
| | '| / Y \ |' | |
| \ \ \ 0 | 0 / / / |
\ '- ,\.-"""""""-./, -' /
''-' /_ ^ ^ _\ '-''
| \._ ._/ |
\ \ '~' / /
'._ '-=-' _.'
'-----'
`
const PROMPT = ">> "
func Start(in io.Reader, out io.Writer, current *user.User) {
_, err := io.WriteString(out, MONKEY)
if err != nil {
log.Fatal(err)
}
_, err = fmt.Fprintf(out, "Hello %s! This is the Monkey programming language!\n", current.Username)
if err != nil {
log.Fatal(err)
}
scanner := bufio.NewScanner(in)
env := object.NewEnvironment()
macroEnv := object.NewEnvironment()
for {
_, err := fmt.Fprintf(out, PROMPT)
if err != nil {
log.Fatal(err)
}
scanned := scanner.Scan()
if !scanned {
return
}
line := scanner.Text()
p := parser.New(line)
program := p.ParseProgram()
if len(p.Errors()) != 0 {
printParseErrors(out, p.Errors())
continue
}
evaluator.DefineMacros(program, macroEnv)
expanded := evaluator.ExpandMacros(program, macroEnv)
evaluated := evaluator.Eval(expanded, env)
if evaluated != nil {
_, err := fmt.Fprintf(out, "%s\n", evaluated.Inspect())
if err != nil {
log.Fatal(err)
}
}
}
}
func printParseErrors(out io.Writer, errors []error) {
_, err := io.WriteString(out, MONKEY)
if err != nil {
log.Fatal(err)
}
_, err = io.WriteString(out, "Whoops! We ran into some monkey business here!\n")
if err != nil {
log.Fatal(err)
}
_, err = io.WriteString(out, "parser errors:\n")
if err != nil {
log.Fatal(err)
}
for _, msg := range errors {
_, err := fmt.Fprintf(out, "\t%s\n", msg)
if err != nil {
log.Fatal(err)
}
}
}