repl: very basic REPL

Author: ncw

main.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 
 	_ "github.com/ncw/gpython/builtin"
+	"github.com/ncw/gpython/repl"
 	//_ "github.com/ncw/gpython/importlib"
 	"io/ioutil"
 	"log"
@@ -52,8 +53,9 @@ func main() {
 	flag.Usage = syntaxError
 	flag.Parse()
 	args := flag.Args()
-	if len(args) != 1 {
-		fatal("Need program to run")
+	if len(args) == 0 {
+		repl.Run()
+		return
 	}
 	prog := args[0]
 	fmt.Printf("Running %q\n", prog)

repl/repl.go

@@ -0,0 +1,47 @@
+// Read Eval Print Loop
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"os"
+
+	"github.com/ncw/gpython/compile"
+	"github.com/ncw/gpython/py"
+	"github.com/ncw/gpython/vm"
+)
+
+func Run() {
+	fmt.Printf("Gpython 3.4.0\n")
+	bio := bufio.NewReader(os.Stdin)
+	module := py.NewModule("__main__", "", nil, nil)
+	prog := "<stdin>"
+	module.Globals["__file__"] = py.String(prog)
+	for {
+		fmt.Printf(">>> ")
+		line, hasMoreInLine, err := bio.ReadLine()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			log.Printf("Error: %v", err)
+			break
+		}
+		if hasMoreInLine {
+			log.Printf("Line truncated")
+		}
+		// FIXME need +"\n" because "single" is broken
+		obj, err := compile.Compile(string(line)+"\n", prog, "single", 0, true)
+		if err != nil {
+			fmt.Printf("Compile error: %v\n", err)
+			continue
+		}
+		code := obj.(*py.Code)
+		_, err = vm.Run(module.Globals, module.Globals, code, nil)
+		if err != nil {
+			py.TracebackDump(err)
+		}
+	}
+}

vm/eval.go

@@ -470,7 +470,17 @@ func do_DELETE_SUBSCR(vm *Vm, arg int32) {
 // expression statement is terminated with POP_STACK.
 func do_PRINT_EXPR(vm *Vm, arg int32) {
 	defer vm.CheckException()
-	vm.NotImplemented("PRINT_EXPR", arg) // FIXME
+	// FIXME this should be calling sys.displayhook
+
+	// Print value except if None
+	// After printing, also assign to '_'
+	// Before, set '_' to None to avoid recursion
+	value := vm.POP()
+	vm.frame.Globals["_"] = py.None
+	if value != py.None {
+		fmt.Printf("%#v\n", value)
+	}
+	vm.frame.Globals["_"] = value
 }
 
 // Terminates a loop due to a break statement.