1 files changed, 50 insertions, 0 deletions
diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 282903b72..d08672cfc 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -25,4 +25,54 @@ printLiteralBool(std::ostream & str, bool boolean)
     return str;
 }
 
+std::ostream &
+printIdentifier(std::ostream & str, std::string_view s) {
+    if (s.empty())
+        str << "\"\"";
+    else if (s == "if") // FIXME: handle other keywords
+        str << '"' << s << '"';
+    else {
+        char c = s[0];
+        if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_')) {
+            printLiteralString(str, s);
+            return str;
+        }
+        for (auto c : s)
+            if (!((c >= 'a' && c <= 'z') ||
+                  (c >= 'A' && c <= 'Z') ||
+                  (c >= '0' && c <= '9') ||
+                  c == '_' || c == '\'' || c == '-')) {
+                printLiteralString(str, s);
+                return str;
+            }
+        str << s;
+    }
+    return str;
+}
+
+// FIXME: keywords
+static bool isVarName(std::string_view s)
+{
+    if (s.size() == 0) return false;
+    char c = s[0];
+    if ((c >= '0' && c <= '9') || c == '-' || c == '\'') return false;
+    for (auto & i : s)
+        if (!((i >= 'a' && i <= 'z') ||
+              (i >= 'A' && i <= 'Z') ||
+              (i >= '0' && i <= '9') ||
+              i == '_' || i == '-' || i == '\''))
+            return false;
+    return true;
+}
+
+std::ostream &
+printAttributeName(std::ostream & str, std::string_view name) {
+    if (isVarName(name))
+        str << name;
+    else
+        printLiteralString(str, name);
+    return str;
+}
+
+
 }