1 files changed, 64 insertions, 0 deletions
diff --git a/maildrop/lexer.h b/maildrop/lexer.h
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+++ b/maildrop/lexer.h
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+#ifndef	lexer_h
+#define	lexer_h
+
+
+#include	"mio.h"
+#include	"buffer.h"
+#include	"token.h"
+
+////////////////////////////////////////////////////////////////////////////
+//
+// Lexer is a lexical scanner - translates a text file into individual
+// tokens.  The Token class is used to represent an individual token, the
+// Lexer class is used to transform a text file into a list of tokens.
+//
+// The scanning algorythm is quite involved.  We may read ahead in the file,
+// then back up.  An 'undo' buffer is maintained.  The actual file is
+// referred to indirectly via the Mio class.
+//
+// The concept of the 'current line number' and 'filename' is also recorded
+// by the Lexer object.  An error message function is provided - given an
+// error message, the filename, and the line number is printer to standard
+// error, followed by the error message.
+//
+////////////////////////////////////////////////////////////////////////////
+
+class	Lexer {
+
+	Mio file;
+	int linenum;
+	Buffer filename;
+	Token::tokentype lasttokentype;
+	// curchar() represents the next character in the file.
+	// Calling curchar() does NOT actual "read" the character, this
+	// is a "peek" function.
+
+	int	curchar() {	return (file.peek()); }
+
+	// nextchar() is used to actually read the next character.
+
+	int	nextchar() { int c=file.get();
+
+				if (c == '\n')	++linenum;
+				return (c);
+			}
+	void	error(const char *);
+
+public:
+	Lexer()	{}
+	~Lexer()	{}
+	int	Open(const char *);	// Open file to read
+	void	token(Token &);		// Scan the next token in
+private:
+	void	token2(Token &);
+public:
+	void	errmsg(const char *);	// Show error message
+	void	errmsg(unsigned long, const char *);
+					// Show error message for a different
+					// line
+	int	Linenum() { return (linenum); }
+					// Return current line number in recipe
+					// file
+} ;
+
+#endif