prog: add helper function parser.HasNext

This helper function will be used in a subsequent commit to take a look
ahead at several characters.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

2 files changed, 38 insertions, 0 deletions

diff --git a/prog/encoding.go b/prog/encoding.go
index 2216955d8..be883645b 100644
--- a/prog/encoding.go
+++ b/prog/encoding.go
@@ -1180,6 +1180,21 @@ func (p *parser) Char() byte {
 	return p.s[p.i]
 }
 
+func (p *parser) HasNext(str string) bool {
+	if p.e != nil {
+		return false
+	}
+	if len(p.s) < p.i+len(str) {
+		return false
+	}
+	for i := 0; i < len(str); i++ {
+		if p.s[p.i+i] != str[i] {
+			return false
+		}
+	}
+	return true
+}
+
 func (p *parser) Parse(ch byte) {
 	if p.e != nil {
 		return
diff --git a/prog/encoding_test.go b/prog/encoding_test.go
index e99663aa3..daa2ac0cb 100644
--- a/prog/encoding_test.go
+++ b/prog/encoding_test.go
@@ -515,3 +515,26 @@ serialize0(0x0)
 		t.Errorf("bad program comments %q\nwant: %q", p.Comments, wantComments)
 	}
 }
+
+func TestHasNext(t *testing.T) {
+	testCases := []struct {
+		input    string
+		expected bool
+	}{
+		{"abcdef", true},
+		{"xyz", false},
+		{"ab", false},
+		{"abc", true},
+	}
+	for _, testCase := range testCases {
+		p := newParser(nil, []byte(testCase.input), true)
+		if !p.Scan() {
+			t.Fatalf("parser does not scan")
+		}
+		result := p.HasNext("abc")
+		if result != testCase.expected {
+			t.Errorf("expected HasNext(\"abc\") on input %q to be %v, but got %v",
+				testCase.input, testCase.expected, result)
+		}
+	}
+}