--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gen/debug_parse.c	Sat Aug 17 21:40:41 2019 +0200
@@ -0,0 +1,8 @@
+#include <stdio.h>
+
+extern int parse(FILE* in);
+
+int main(void) {
+    parse(stdin);
+    return 0;
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gen/y.yy	Sat Aug 17 21:40:41 2019 +0200
@@ -0,0 +1,59 @@
+
+%pointer
+
+%top {
+#include <stdio.h>
+}
+
+%{
+
+int yywrap() { return 1; }
+
+typedef enum { LEFT, RIGHT } Paren;
+
+void paren(Paren p) {
+    if (p == LEFT) printf("left paren!\n");
+    if (p == RIGHT) printf("right paren!\n");
+}
+
+void atom(const char* txt) {
+    printf("atom: %s\n", txt);
+}
+
+void number(const char* txt) {
+    printf("number: %s\n", txt);
+}
+
+%}
+
+
+SPACE   [[:blank:]]+
+LEFTP   "("
+RIGHTP  ")"
+ATOM    [a-z][a-z0-9]*
+NUMBER  [1-9][0-9]*
+
+%%
+
+{SPACE}   { }
+{LEFTP}   { paren(LEFT); }
+{RIGHTP}  { paren(RIGHT); }
+{ATOM}    { atom(yytext); }
+{NUMBER}  { number(yytext); }
+
+%%
+
+// Parse input from in. Closes after finishing.
+int parse(FILE* in) {
+    #ifndef DEBUG
+    FILE* out = fopen("/dev/null", "w");
+    #else
+    FILE* out = stdout;
+    #endif
+    yyout = out;
+    yyin = in;
+    yylex();
+    fclose(in);
+    fclose(out);
+    return 0;
+}