Introduced the evaluator (and integrated it with the REPL)

It supports integer and boolean literals, prefix expressions and infix
expressions with integer operands.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/evaluator/evaluator_test.go

@@ -0,0 +1,108 @@
+package evaluator
+
+import (
+	"testing"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/lexer"
+	"code.jmug.me/jmug/interpreter-in-go/pkg/object"
+	"code.jmug.me/jmug/interpreter-in-go/pkg/parser"
+)
+
+func TestEvalIntegerExpression(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"5", 5},
+		{"10", 10},
+		{"-5", -5},
+		{"-10", -10},
+		{"5 + 5 + 5 + 5 - 10", 10},
+		{"2 * 2 * 2 * 2 * 2", 32},
+		{"-50 + 100 + -50", 0},
+		{"5 * 2 + 10", 20},
+		{"5 + 2 * 10", 25},
+		{"20 + 2 * -10", 0},
+		{"50 / 2 * 2 + 10", 60},
+		{"2 * (5 + 10)", 30},
+		{"3 * 3 * 3 + 10", 37},
+		{"3 * (3 * 3) + 10", 37},
+		{"(5 + 10 * 2 + 15 / 3) * 2 + -10", 50},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}
+
+func TestEvalBooleanExpression(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected bool
+	}{
+		{"true", true},
+		{"false", false},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testBooleanObject(t, evaluated, tt.expected)
+	}
+}
+
+func TestBangOperator(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected bool
+	}{
+		{"!true", false},
+		{"!false", true},
+		{"!5", false},
+		{"!!true", true},
+		{"!!false", false},
+		{"!!5", true},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testBooleanObject(t, evaluated, tt.expected)
+	}
+}
+
+func testEval(input string) object.Object {
+	l := lexer.New(input)
+	p := parser.New(l)
+	program := p.ParseProgram()
+
+	return 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
+}
+
+func testBooleanObject(t *testing.T, obj object.Object, expected bool) bool {
+	result, ok := obj.(*object.Boolean)
+	if !ok {
+		t.Errorf("object is not Boolean. got=%T (%+v)", obj, obj)
+		return false
+	}
+	if result.Value != expected {
+		t.Errorf("object has wrong value. got=%t, want=%t",
+			result.Value, expected)
+		return false
+	}
+	return true
+}