Extract line reading logic to reader and remove REPL tests

Reading a line into the buffer was the only logic complex enough to be
worth testing really, and exposing the necessary parts of it to test
it effectively was a pain.  Makes more sense to move read_line out and
throw away most of the tests.

lib/repl.c

@@ -1,5 +1,8 @@
 #include "repl.h"
 
+#include "evaluator.h"
+#include "reader.h"
+
 #include <stdio.h>
 #include <string.h>
 
@@ -7,26 +10,17 @@ bool step_repl(repl_t *repl)
 {
 	init_memory_pool(&repl->pool);
 
-	int len;
-	for (len = 0; len < REPL_LINE_BUFFER_SIZE; ++len) {
-		const int byte = repl->get_byte();
-		if (EOF == byte)
-			return false;
-		else if ('\n' == byte)
-			break;
-		repl->line_buffer[len] = (char)byte;
-	}
-	const expression_t *e = repl->read(&repl->pool, repl->line_buffer, len);
+	const int len = read_line(getchar, repl->buffer, REPL_BUFFER_SIZE);
+	if (len < 0)
+		return false;
+	const expression_t *e = read_expression(&repl->pool, repl->buffer, len);
 	if (NULL == e) {
-		const char *msg = "Invalid expression\n";
-		repl->print(msg, strlen(msg));
+		puts("Invalid expression\n");
 		return true;
 	}
 
-	const int result = repl->evaluate(e);
-	const int result_len = snprintf(
-	    repl->result_buffer, REPL_RESULT_BUFFER_SIZE, "%d\n", result);
-	repl->print(repl->result_buffer, result_len);
+	const int result = evaluate(e);
+	printf("%d\n", result);
 
 	return true;
 }