Minor code reorganization, handled tab characters correctly

src/io.c

@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <io.h>
+
+static char *append(char *str, char c, size_t *len, size_t *alloc);
+
+void ungetline(struct linefile *file, char *line) {
+	file->prevline = line;
+}
+
+char *getline(struct linefile *file) {
+	size_t alloc;
+	size_t len;
+	char *ret;
+	int c;
+
+	if (file->prevline != NULL) {
+		ret = file->prevline;
+		file->prevline = NULL;
+		return ret;
+	}
+
+	c = fgetc(file->file);
+	if (c == EOF)
+		return NULL;
+	ungetc(c, file->file);
+
+	alloc = 80;
+	len = 0;
+	ret = malloc(alloc);
+	if (ret == NULL)
+		return NULL;
+
+	for (;;) {
+		c = fgetc(file->file);
+		if (c == '\n') {
+			ret[len] = '\0';
+			return ret;
+		}
+		if (c == '\t') {
+			while (len % 4 != 0) {
+				ret = append(ret, ' ', &len, &alloc);
+				if (ret == NULL)
+					return NULL;
+			}
+		}
+		else {
+			ret = append(ret, c, &len, &alloc);
+			if (ret == NULL)
+				return NULL;
+		}
+	}
+}
+
+struct linefile *newlinefile(FILE *file) {
+	struct linefile *ret;
+	ret = malloc(sizeof *ret);
+	ret->prevline = NULL;
+	ret->file = file;
+	return ret;
+}
+
+void freelinefile(struct linefile *file) {
+	free(file->prevline);
+	fclose(file->file);
+	free(file);
+}
+
+static char *append(char *str, char c, size_t *len, size_t *alloc) {
+	if (*len >= *alloc) {
+		char *newstr;
+		*alloc *= 2;
+		newstr = realloc(str, *alloc);
+		if (newstr == NULL) {
+			free(str);
+			return NULL;
+		}
+		str = newstr;
+	}
+	str[(*len)++] = c;
+	return str;
+}