frontend: add a line editor for shell input

frontend/line-ed/prompt.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include "line-ed.h"
+#include "prompt.h"
+
+void show_prompt(struct line_ed *ed)
+{
+	int type = PROMPT_MAIN;
+	if (ed->l_scope_type) {
+		type = PROMPT_CONT;
+
+		/* this is a temporary solution to show the current
+		 * scope type, until prompts are implemented properly. */
+		fputs(ed->l_scope_type, stdout);
+	}
+
+	if (ed->l_continuations > 0) {
+		type = PROMPT_CONT;
+	}
+
+	fputs(ed->l_prompt[type], stdout);
+	fflush(stdout);
+}
+
+unsigned long prompt_length(struct line_ed *ed, int prompt_id)
+{
+	return strlen(ed->l_prompt[prompt_id]);
+}