diff --git a/src/apfl.h b/src/apfl.h
index 799a20a..fbd6c57 100644
--- a/src/apfl.h
+++ b/src/apfl.h
@@ -473,9 +473,27 @@ struct apfl_tokenizer;
 
 typedef struct apfl_tokenizer *apfl_tokenizer_ptr;
 
-typedef bool (*apfl_source_reader_cb)(void *context, char *buf, size_t *len, bool need);
+/* An apfl_source_reader is used to read source code for parsing / evaluation.
+ */
+struct apfl_source_reader {
+    /* callback gets called repeatedly to get the source code.
+     * buf points to a buffer to fill that has a size of *len.
+     * The callback must set len to the number of read bytes and return true
+     * on success and false on failure.
+     *
+     * Setting len to 0 indicates and end of file.
+     *
+     * need is true if more input is required for parsing, this is useful for
+     * implementing a reader for a REPL to indicate to the user if they need
+     * to type more code (e.g. by changing the prompt).
+     */
+    bool (*callback)(void *opaque, char *buf, size_t *len, bool need);
+
+    void *opaque;
+};
+
+apfl_tokenizer_ptr apfl_tokenizer_new(struct apfl_allocator allocator, struct apfl_source_reader);
 
-apfl_tokenizer_ptr apfl_tokenizer_new(struct apfl_allocator allocator, apfl_source_reader_cb, void *context);
 void apfl_tokenizer_destroy(apfl_tokenizer_ptr);
 
 enum apfl_parse_result apfl_tokenizer_next(apfl_tokenizer_ptr, bool need);
@@ -492,15 +510,21 @@ struct apfl_token apfl_tokenizer_get_token(apfl_tokenizer_ptr);
  */
 struct apfl_error apfl_tokenizer_get_error(apfl_tokenizer_ptr);
 
-
-/* An apfl_source_reader_cb implementation to have a string view as a source.
- * Use together with apfl_string_source_reader_new.
+/* apfl_string_source_reader_* implements an apfl_source_reader that reads
+ * source code from a string view.
  */
-bool apfl_string_source_reader(void *, char *, size_t *len, bool);
+struct apfl_string_source_reader_data {
+    struct apfl_string_view sv;
+    size_t off;
+};
 
-void *apfl_string_source_reader_new(struct apfl_allocator allocator, struct apfl_string_view);
-void apfl_string_source_reader_destroy(void *);
+struct apfl_string_source_reader_data apfl_string_source_reader_create(struct apfl_string_view);
 
+/* Creates a source reader for apfl_string_source_reader_data.
+ * The pointed to apfl_string_source_reader_data and the underlying string view
+ * must be alive while the reader is in use.
+ */
+struct apfl_source_reader apfl_string_source_reader(struct apfl_string_source_reader_data *);
 
 struct apfl_parser_token_source {
     enum apfl_parse_result (*next)(void *, bool need);
diff --git a/src/main.c b/src/main.c
index c3048fc..bd3f6f1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -12,7 +12,7 @@ enum repl_mode {
 };
 
 static bool
-repl_source_reader(void *context, char *buf, size_t *len, bool need)
+repl_source_reader_cb(void *context, char *buf, size_t *len, bool need)
 {
     (void)context;
 
@@ -34,6 +34,15 @@ repl_source_reader(void *context, char *buf, size_t *len, bool need)
     return true;
 }
 
+static struct apfl_source_reader
+repl_source_reader()
+{
+    return (struct apfl_source_reader) {
+        .callback = repl_source_reader_cb,
+        .opaque = NULL,
+    };
+}
+
 static int
 repl_tokenizer(struct apfl_allocator allocator, apfl_tokenizer_ptr tokenizer)
 {
@@ -146,7 +155,7 @@ main(int argc, const char **argv)
     apfl_parser_ptr parser = NULL;
     apfl_ctx ctx = NULL;
 
-    if ((tokenizer = apfl_tokenizer_new(allocator, repl_source_reader, NULL)) == NULL) {
+    if ((tokenizer = apfl_tokenizer_new(allocator, repl_source_reader())) == NULL) {
         fprintf(stderr, "Failed initializing tokenizer\n");
         rv = 1;
         goto exit;
diff --git a/src/parser_test.c b/src/parser_test.c
index c91cb58..e5e36b4 100644
--- a/src/parser_test.c
+++ b/src/parser_test.c
@@ -9,7 +9,7 @@
 struct parser_test {
     testctx t;
     struct apfl_allocator allocator;
-    void *source_reader_ctx;
+    struct apfl_string_source_reader_data string_source_reader;
     apfl_tokenizer_ptr tokenizer;
     apfl_parser_ptr parser;
 };
@@ -23,11 +23,12 @@ new_parser_test(testctx t, const char *source)
     pt->t = t;
     pt->allocator = allocator;
 
-    if ((pt->source_reader_ctx = apfl_string_source_reader_new(allocator, apfl_string_view_from(source))) == NULL) {
-        test_fatalf(t, "Failed initializing source reader");
-    }
+    pt->string_source_reader = apfl_string_source_reader_create(apfl_string_view_from(source));
 
-    if ((pt->tokenizer = apfl_tokenizer_new(allocator, apfl_string_source_reader, pt->source_reader_ctx)) == NULL) {
+    if ((pt->tokenizer = apfl_tokenizer_new(
+        allocator,
+        apfl_string_source_reader(&pt->string_source_reader)
+    )) == NULL) {
         test_fatalf(t, "Failed initializing the tokenizer");
     }
 
@@ -43,7 +44,6 @@ destroy_parser_test(struct parser_test *pt)
 {
     apfl_parser_destroy(pt->parser);
     apfl_tokenizer_destroy(pt->tokenizer);
-    apfl_string_source_reader_destroy(pt->source_reader_ctx);
     free(pt);
 }
 
diff --git a/src/source_readers.c b/src/source_readers.c
index 16195c4..6adcef6 100644
--- a/src/source_readers.c
+++ b/src/source_readers.c
@@ -3,20 +3,12 @@
 
 #include "apfl.h"
 
-#include "alloc.h"
-
-struct string_source_reader {
-    struct apfl_allocator allocator;
-    struct apfl_string_view sv;
-    size_t off;
-};
-
-bool
-apfl_string_source_reader(void *opaque, char *buf, size_t *len, bool need)
+static bool
+reader_callback(void *opaque, char *buf, size_t *len, bool need)
 {
     (void)need;
 
-    struct string_source_reader *ctx = opaque;
+    struct apfl_string_source_reader_data *ctx = opaque;
 
     size_t maxlen = *len;
     size_t remain_len = ctx->sv.len - ctx->off;
@@ -28,28 +20,19 @@ apfl_string_source_reader(void *opaque, char *buf, size_t *len, bool need)
     return true;
 }
 
-void *
-apfl_string_source_reader_new(struct apfl_allocator allocator, struct apfl_string_view sv)
+struct apfl_string_source_reader_data
+apfl_string_source_reader_create(struct apfl_string_view sv)
 {
-    struct string_source_reader *ctx = ALLOC_OBJ(allocator, struct string_source_reader);
-    if (ctx == NULL) {
-        return NULL;
-    }
-
-    ctx->allocator = allocator;
-    ctx->sv = sv;
-    ctx->off = 0;
-
-    return ctx;
+    return (struct apfl_string_source_reader_data) {
+        .sv = sv,
+        .off = 0,
+    };
 }
 
-void
-apfl_string_source_reader_destroy(void *opaque)
+struct apfl_source_reader apfl_string_source_reader(struct apfl_string_source_reader_data *data)
 {
-    struct string_source_reader *ctx = opaque;
-    if (ctx == NULL) {
-        return;
-    }
-
-    FREE_OBJ(ctx->allocator, ctx);
+    return (struct apfl_source_reader) {
+        .callback = reader_callback,
+        .opaque = data,
+    };
 }
diff --git a/src/tokenizer.c b/src/tokenizer.c
index 15fd6a5..d445af9 100644
--- a/src/tokenizer.c
+++ b/src/tokenizer.c
@@ -16,8 +16,7 @@ static_assert(INT_MAX >= BUFSIZE, "BUFSIZE is too large for type buf_offset");
 
 struct apfl_tokenizer {
     struct apfl_allocator allocator;
-    apfl_source_reader_cb source_reader;
-    void *source_reader_context;
+    struct apfl_source_reader source_reader;
     char *buf;
     buf_offset buf_pos;
     buf_offset buf_len;
@@ -42,7 +41,7 @@ struct apfl_tokenizer {
 };
 
 apfl_tokenizer_ptr
-apfl_tokenizer_new(struct apfl_allocator allocator, apfl_source_reader_cb source_reader, void *context)
+apfl_tokenizer_new(struct apfl_allocator allocator, struct apfl_source_reader source_reader)
 {
     apfl_tokenizer_ptr tokenizer = ALLOC_OBJ(allocator, struct apfl_tokenizer);
     if (tokenizer == NULL) {
@@ -51,7 +50,6 @@ apfl_tokenizer_new(struct apfl_allocator allocator, apfl_source_reader_cb source
 
     tokenizer->allocator = allocator;
     tokenizer->source_reader = source_reader;
-    tokenizer->source_reader_context = context;
 
     if ((tokenizer->buf = ALLOC_BYTES(allocator, BUFSIZE)) == NULL) {
         FREE_OBJ(allocator, tokenizer);
@@ -110,7 +108,7 @@ read_byte(apfl_tokenizer_ptr tokenizer, char *byte, bool need)
         tokenizer->buf_pos = 0;
         tokenizer->buf_len = 0;
 
-        if (!tokenizer->source_reader(tokenizer->source_reader_context, tokenizer->buf, &len, need)) {
+        if (!tokenizer->source_reader.callback(tokenizer->source_reader.opaque, tokenizer->buf, &len, need)) {
             tokenizer->error.type = APFL_ERR_INPUT_ERROR;
             return RR_ERR;
         }
diff --git a/src/tokenizer_test.c b/src/tokenizer_test.c
index be40829..f4948c0 100644
--- a/src/tokenizer_test.c
+++ b/src/tokenizer_test.c
@@ -8,7 +8,7 @@ struct tokenizer_test {
     testctx t;
     struct apfl_allocator allocator;
     apfl_tokenizer_ptr tokenizer;
-    void *ctx;
+    struct apfl_string_source_reader_data string_source_reader;
 };
 
 static struct tokenizer_test *
@@ -16,25 +16,20 @@ new_tokenizer_test_sv(testctx t, struct apfl_string_view text)
 {
     struct apfl_allocator allocator = apfl_allocator_default();
 
-    void *ctx = apfl_string_source_reader_new(allocator, text);
-    if (ctx == NULL) {
-        test_fatalf(t, "Failed to initialize the source reader");
-    }
-
-    apfl_tokenizer_ptr tokenizer = apfl_tokenizer_new(allocator, apfl_string_source_reader, ctx);
-    if (tokenizer == NULL) {
-        test_fatalf(t, "Failed to initialize the tokenizer");
-    }
-
     struct tokenizer_test *tt = must_alloc(t, sizeof(struct tokenizer_test));
-
     *tt = (struct tokenizer_test) {
         .t = t,
         .allocator = allocator,
-        .tokenizer = tokenizer,
-        .ctx = ctx,
+        .string_source_reader = apfl_string_source_reader_create(text),
     };
 
+    if ((tt->tokenizer = apfl_tokenizer_new(
+        allocator,
+        apfl_string_source_reader(&tt->string_source_reader)
+    )) == NULL) {
+        test_fatalf(t, "Failed to initialize the tokenizer");
+    }
+
     return tt;
 }
 
@@ -48,7 +43,6 @@ new_tokenizer_test(testctx t, const char *text)
 static void
 destroy_tokenizer_test(struct tokenizer_test *tt)
 {
-    apfl_string_source_reader_destroy(tt->ctx);
     apfl_tokenizer_destroy(tt->tokenizer);
     free(tt);
 }