Fix #555

compiler/bytecode/expression_generation.go

@@ -244,6 +244,8 @@ func (g *Generator) compilePrefixExpression(is *InstructionSet, exp *ast.PrefixE
 		is.define(PutObject, exp.Line(), 0)
 		g.compileExpression(is, exp.Right, scope, table)
 		is.define(Send, exp.Line(), exp.Operator, 1, "", &ArgSet{})
+	case "+":
+		g.compileExpression(is, exp.Right, scope, table)
 	}
 }
 

compiler/parser/expression_parsing_test.go

@@ -698,7 +698,8 @@ func TestArithmeticExpressionFail(t *testing.T) {
 		input string
 		error string
 	}{
-		{`{ 1 ++ 1 }`, `unexpected + Line: 0`},
+		{`{ 1 ++ 1 }`, `expected next token to be }, got +(+) instead. Line: 0`},
+		{`{ 1 -- 1 }`, `expected next token to be }, got -(-) instead. Line: 0`},
 		{`{ 1 * * 1 }`, `unexpected * Line: 0`},
 		{`{ 1 ** [1, 2] }`, `expected next token to be }, got **(**) instead. Line: 0`},
 	}

compiler/parser/parser.go

@@ -70,6 +70,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(token.False, p.parseBooleanLiteral)
 	p.registerPrefix(token.Null, p.parseNilExpression)
 	p.registerPrefix(token.Minus, p.parsePrefixExpression)
+	p.registerPrefix(token.Plus, p.parsePrefixExpression)
 	p.registerPrefix(token.Asterisk, p.parsePrefixExpression)
 	p.registerPrefix(token.Bang, p.parsePrefixExpression)
 	p.registerPrefix(token.LParen, p.parseGroupedExpression)

vm/evaluation_test.go

@@ -2242,6 +2242,26 @@ func TestMinusPrefixMethodCall(t *testing.T) {
 	}
 }
 
+func TestPlusPrefixMethodCall(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int
+	}{
+		{"+5", 5},
+		{"+10", 10},
+		{"+(-10)", -10},
+		{"+(-5)", -5},
+	}
+
+	for i, tt := range tests {
+		v := initTestVM()
+		evaluated := v.testEval(t, tt.input, getFilename())
+		VerifyExpected(t, i, evaluated, tt.expected)
+		v.checkCFP(t, i, 0)
+		v.checkSP(t, i, 1)
+	}
+}
+
 func TestMultiVarAssignment(t *testing.T) {
 	tests := []struct {
 		input    string