From 392fc74a77b94cc78e9bfe349dcdfa0ab8fc8f5c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Fri, 10 Jun 2022 18:03:44 +0200
Subject: Simple lex implementation.

---
 .gitignore |  6 ++++++
 Makefile   |  7 +++++++
 xroff.lex  | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 xroff.lex

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f22fb6c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+*~
+lex.yy.c
+xroff
+xroff.exe
+*.pdf
+*.ps
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..80cc949
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,7 @@
+CC = gcc
+
+xroff: lex.yy.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -o xroff lex.yy.c
+
+lex.yy.c: xroff.lex
+	flex xroff.lex
diff --git a/xroff.lex b/xroff.lex
new file mode 100644
index 0000000..6282ca1
--- /dev/null
+++ b/xroff.lex
@@ -0,0 +1,69 @@
+%option noyywrap
+%x NEW
+%x REQ
+%x RAW
+%x ESC
+%x RES
+
+%%
+
+\\		BEGIN(ESC);
+\n		BEGIN(NEW);
+\<!\[		BEGIN(RAW);
+^<		printf("."); BEGIN(REQ);	/* Beginning of file. */
+\<		printf("\\c\n."); BEGIN(REQ);
+.		ECHO;
+
+	/* Handle text following newlines. */
+
+<NEW>\n		/* Ignore consecutive newlines. */
+<NEW>\\		printf("\n"); BEGIN(ESC);
+<NEW>\<!\[\n?	printf("\n"); BEGIN(RAW);
+<NEW><		printf("\n."); BEGIN(REQ);
+<NEW>\.		printf("\n\\&."); BEGIN(0);
+<NEW>.		printf("\n"); BEGIN(0); REJECT;
+
+	/* Translate request. */
+
+<REQ>\\		BEGIN(RES);
+<REQ>>		BEGIN(NEW);
+
+	/* Pass through raw troff code. */
+
+<RAW>\n\]>	BEGIN(NEW);
+<RAW>\]>	BEGIN(0);
+<RAW>.		ECHO;
+
+	/* Escape next character. */
+
+<ESC>\\		printf("\\\\"); BEGIN(0);
+<ESC><		ECHO; BEGIN(0);
+<ESC>.		printf("\\"); ECHO; BEGIN(0);
+
+	/* Escape next character within request. */
+
+<RES>\\		printf("\\\\"); BEGIN(REQ);
+<RES>>		ECHO; BEGIN(REQ);
+<RES>.		printf("\\"); ECHO; BEGIN(REQ);
+
+%%
+
+int
+main()
+{
+	char *st;
+
+	yylex();
+
+	switch (YYSTATE) {
+	case 0: return 0;
+	case NEW: printf("\n"); return 0;
+	case REQ: st = "request"; break;
+	case RAW: st = "raw section"; break;
+	case ESC: st = "escape"; break;
+	case RES: st = "escape (within request)"; break;
+	}
+
+	fprintf(stderr, "%s unfinished\n", st);
+	return 1;
+}
-- 
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