2 files changed, 69 insertions, 2 deletions

diff --git a/parser/parser.go b/parser/parser.go
index 32bb4bc..d236bf0 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -115,7 +115,7 @@ func (p *Parser) parseIdentifier() ast.Expression {
 
 // parseIntegerLiteral parses an integer literal.
 func (p *Parser) parseIntegerLiteral() ast.Expression {
-	var lit *ast.IntegerLiteral = &ast.IntegerLiteral{ Token: p.curToken }
+	var lit *ast.IntegerLiteral = &ast.IntegerLiteral{Token: p.curToken}
 
 	var value, err = strconv.ParseInt(p.curToken.Literal, 0, 64)
 	if err != nil {
diff --git a/parser/parser_test.go b/parser/parser_test.go
index cd1d506..828db24 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -1,6 +1,7 @@
 package parser
 
 import (
+	"fmt"
 	"mana/ast"
 	"mana/lexer"
 	"testing"
@@ -182,7 +183,6 @@ func TestIntegerLiteralExpression(t *testing.T) {
 		t.Fatalf("exp not *ast.IntegerLiteral. got=%T", stmt.Expression)
 	}
 
-
 	if literal.Value != 5 {
 		t.Errorf("literal.Value not %d. got=%d", 5, literal.Value)
 	}
@@ -192,3 +192,70 @@ func TestIntegerLiteralExpression(t *testing.T) {
 	}
 }
 
+// Prefix expression tests.
+
+func TestParsingPrefixExpressions(t *testing.T) {
+	var prefixTests = []struct {
+		input        string
+		operator     string
+		integerValue int64
+	}{
+		{"!5;", "!", 5},
+		{"-15;", "-", 15},
+	}
+
+	for _, tt := range prefixTests {
+		var l *lexer.Lexer = lexer.New(tt.input)
+		var p *Parser = New(l)
+		var program *ast.Program = p.ParseProgram()
+		checkParserErrors(t, p)
+
+		if len(program.Statements) != 1 {
+			t.Fatalf("program.Statements does not contain %d statements. got=%d", 1, len(program.Statements))
+		}
+
+		stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+
+		if !ok {
+			t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T", program.Statements[0])
+		}
+
+		exp, ok := stmt.Expression.(*ast.PrefixExpression)
+
+		if !ok {
+			t.Fatalf("stmt is not ast.PrefixExpression. got=%T", stmt.Expression)
+		}
+
+		if exp.Operator != tt.operator {
+			t.Fatalf("exp.Operator is not '%s'. got=%s", tt.operator, exp.Operator)
+		}
+
+		if !testIntegerLiteral(t, exp.Right, tt.integerValue) {
+			return
+		}
+	}
+}
+
+func testIntegerLiteral(t *testing.T, il ast.Expression, value int64) bool {
+	var integ, ok = il.(*ast.IntegerLiteral)
+
+	if !ok {
+		t.Errorf("il not *ast.IntegerLiteral. got=%T", il)
+
+		return false
+	}
+
+	if integ.Value != value {
+		t.Errorf("integ.Value not %d. got=%d", value, integ.Value)
+
+		return false
+	}
+
+	if integ.TokenLiteral() != fmt.Sprintf("%d", value) {
+		t.Errorf("integ.TokenLiteral not %d. got=%s", value, integ.TokenLiteral())
+
+		return false
+	}
+
+	return true
+}