--- /dev/null
+#ifndef _PSI_LEXER_H
+#define _PSI_LEXER_H
+
+#ifndef BSIZE
+# define BSIZE 256
+#endif
+
+typedef struct PSI_Lexer {
+
+} PSI_Lexer;
+
+size_t PSI_LexerFill(PSI_Lexer *L, size_t n);
+void PSI_LexerDtor(PSI_Lexer *L);
+void PSI_LexerFree(PSI_Lexer **L);
+PSI_Lexer *PSI_LexerInit(PSI_Lexer *L, const char *filename);
+token_t PSI_LexerScan(PSI_Lexer *L);
+
+#endif