Start of chapter 3, modified, eval literals and repl

Author: ldemailly

.gitignore

@@ -28,3 +28,4 @@ gorpl
 
 .DS_Store
 __*
+*_string.go

.vscode/launch.json

@@ -0,0 +1,13 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Launch Package",
+            "type": "go",
+            "request": "launch",
+            "mode": "auto",
+            "console": "integratedTerminal", // so we can type input
+            "program": "${fileDirname}"
+        }
+    ]
+}

eval/eval.go

@@ -0,0 +1,36 @@
+package eval
+
+import (
+	"fmt"
+
+	"github.com/ldemailly/gorpl/ast"
+	"github.com/ldemailly/gorpl/object"
+)
+
+func Eval(node any) object.Object {
+	switch node := node.(type) {
+	// Statements
+	case *ast.Program:
+		return evalStatements(node.Statements)
+
+	case *ast.ExpressionStatement:
+		return Eval(node.Val)
+
+	// Expressions
+	case *ast.IntegerLiteral:
+		return &object.Integer{Value: node.Val}
+	}
+
+	return &object.Error{Value: fmt.Sprintf("unknown node type: %T", node)}
+}
+
+func evalStatements(stmts []ast.Node) object.Object {
+	var result object.Object
+	result = &object.Null{} // no crash when empty program.
+
+	for _, statement := range stmts {
+		result = Eval(statement)
+	}
+
+	return result
+}

eval/eval_test.go

@@ -0,0 +1,48 @@
+package eval_test
+
+import (
+	"testing"
+
+	"github.com/ldemailly/gorpl/eval"
+	"github.com/ldemailly/gorpl/lexer"
+	"github.com/ldemailly/gorpl/object"
+	"github.com/ldemailly/gorpl/parser"
+)
+
+func TestEvalIntegerExpression(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"5", 5},
+		{"10", 10},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}
+
+func testEval(input string) object.Object {
+	l := lexer.New(input)
+	p := parser.New(l)
+	program := p.ParseProgram()
+
+	return eval.Eval(program)
+}
+
+func testIntegerObject(t *testing.T, obj object.Object, expected int64) bool {
+	result, ok := obj.(*object.Integer)
+	if !ok {
+		t.Errorf("object is not Integer. got=%T (%+v)", obj, obj)
+		return false
+	}
+	if result.Value != expected {
+		t.Errorf("object has wrong value. got=%d, want=%d",
+			result.Value, expected)
+		return false
+	}
+
+	return true
+}

object/object.go

@@ -0,0 +1,60 @@
+package object
+
+import (
+	"strconv"
+)
+
+type Type uint8
+
+type Object interface {
+	Type() Type
+	Inspect() string
+}
+
+const (
+	UNKNOWN Type = iota
+	INTEGER
+	BOOLEAN
+	NULL
+	ERROR
+	LAST
+)
+
+//go:generate stringer -type=Type
+var _ = LAST.String() // force compile error if go generate is missing.
+
+type Integer struct {
+	Value int64
+}
+
+func (i *Integer) Inspect() string {
+	return strconv.FormatInt(i.Value, 10)
+}
+
+func (i *Integer) Type() Type {
+	return INTEGER
+}
+
+type Boolean struct {
+	Value bool
+}
+
+func (b *Boolean) Type() Type {
+	return BOOLEAN
+}
+
+func (b *Boolean) Inspect() string {
+	return strconv.FormatBool(b.Value)
+}
+
+type Null struct{}
+
+func (n *Null) Type() Type      { return NULL }
+func (n *Null) Inspect() string { return "<null>" }
+
+type Error struct {
+	Value string // message
+}
+
+func (e *Error) Type() Type      { return ERROR }
+func (e *Error) Inspect() string { return "<err: " + e.Value + ">" }

repl/repl.go

@@ -5,21 +5,23 @@ import (
 	"fmt"
 	"io"
 
+	"fortio.org/log"
+	"github.com/ldemailly/gorpl/eval"
 	"github.com/ldemailly/gorpl/lexer"
 	"github.com/ldemailly/gorpl/parser"
 )
 
 const PROMPT = "$ "
 
-func printParserErrors(out io.Writer, p *parser.Parser) bool {
+func logParserErrors(p *parser.Parser) bool {
 	errors := p.Errors()
 	if len(errors) == 0 {
 		return false
 	}
 
-	fmt.Fprintf(out, "parser has %d error(s)\n", len(errors))
+	log.Critf("parser has %d error(s)", len(errors))
 	for _, msg := range errors {
-		fmt.Fprintf(out, "parser error: %s\n", msg)
+		log.Errf("parser error: %s", msg)
 	}
 	return true
 }
@@ -39,9 +41,13 @@ func Start(in io.Reader, out io.Writer) {
 
 		p := parser.New(l)
 		program := p.ParseProgram()
-		if printParserErrors(out, p) {
+		if logParserErrors(p) {
 			continue
 		}
+		fmt.Print("== Parse ==> ")
 		fmt.Println(program.String())
+		fmt.Print("== Eval  ==> ")
+		obj := eval.Eval(program)
+		fmt.Println(obj.Inspect())
 	}
 }