From 358fe01fc2a0e1c5765179d8b3c8cbc85c4a2cbd Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Tue, 8 Jun 2021 13:38:33 -0400
Subject: [PATCH] Issue #211 - production version of (char-ready?)

---
 CHANGELOG.md              |  1 +
 include/cyclone/runtime.h |  1 +
 runtime.c                 | 33 ++++++---------------------------
 scheme/base.sld           |  9 +++++++++
 4 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9db258c1..188b927a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ Features
 - Improve performance of runtime by more efficiently unboxing known fixnums. 
 - Improve performance of compiled code slightly by using more efficient closure calls when possible.
 - Add support for R7RS `#d` decimal specifier for numbers.
+- Added `char-ready?` to `(scheme base)`
 
 Bug Fixes
 
diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index e0978bb6..d175fb68 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -368,6 +368,7 @@ object Cyc_io_close_output_port(void *data, object port);
 object Cyc_io_flush_output_port(void *data, object port);
 object Cyc_io_read_char(void *data, object cont, object port);
 object Cyc_io_peek_char(void *data, object cont, object port);
+object Cyc_io_char_ready(void *data, object port);
 object Cyc_write_u8(void *data, object c, object port);
 object Cyc_io_read_u8(void *data, object cont, object port);
 object Cyc_io_peek_u8(void *data, object cont, object port);
diff --git a/runtime.c b/runtime.c
index 3f719383..97d417b1 100644
--- a/runtime.c
+++ b/runtime.c
@@ -7728,21 +7728,16 @@ static void _read_return_atom(void *data, object cont, port_type *p)
 
 object Cyc_io_char_ready(void *data, object port)
 {
-  FILE *stream;
-  port_type *p;
-
   Cyc_check_port(data, port);
   {
-    p = (port_type *)port;
-    stream = ((port_type *) port)->fp;
+    port_type *p = (port_type *)port;
+    FILE *stream = p->fp;
     if (stream == NULL) {
       Cyc_rt_raise2(data, "Unable to read from closed port: ", port);
     }
 
-// TODO: this may be linux-specific
-// TODO: what about EOF?
     if (p->mem_buf_len == 0 || p->mem_buf_len == p->buf_idx) {
-      // TODO: slow path, does stream have data ready?
+      // Slow path, check if underlying stream has data ready
       int fd = fileno(stream);
       fd_set rfds;
       struct timeval tv;
@@ -7751,10 +7746,11 @@ object Cyc_io_char_ready(void *data, object port)
       FD_SET(fd, &rfds);
       tv.tv_sec = 0;
       tv.tv_usec = 0;
-      retval = select(fd + 1, &rfds, NULL, NULL, &tv);
+      retval = select(fd + 1, &rfds, NULL, NULL, &tv); // Non-blocking fd check 
       return (retval ? boolean_t : boolean_f); 
     } else {
-      return boolean_t;
+      // Fast path, port has buffered data ready to go
+      return boolean_t; 
     }
   }
 }
@@ -7849,23 +7845,6 @@ object Cyc_io_peek_u8(void *data, object cont, object port)
   return Cyc_EOF;
 }
 
-// TODO: full requirements are:
-//
-// Returns #t if a character is ready on the textual input
-// port and returns #f otherwise. If char-ready returns #t
-// then the next read-char operation on the given port is
-// guaranteed not to hang. If the port is at end of file then
-// char-ready? returns #t.
-//
-// This is a bit of a challenge because the internal buffers 
-// cannot differentiate between being empty and being at EOF.
-//
-//object Cyc_io_char_ready(void *data, object cont, object port)
-//{
-//  port_type *p = (port_type *)port;
-//  Cyc_check_port(data, port);
-//}
-
 object Cyc_io_read_char(void *data, object cont, object port)
 {
   port_type *p = (port_type *)port;
diff --git a/scheme/base.sld b/scheme/base.sld
index 018dee6b..9bd3c826 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -145,6 +145,7 @@
     write-string-1
     write-string-2
     flush-output-port
+    char-ready?
     peek-char
     read-char
     read-line
@@ -676,6 +677,14 @@
       (if (null? port)
         (_write-u8 chr (current-output-port))
         (_write-u8 chr (car port))))
+    (define-c Cyc-char-ready?
+      "(void *data, int argc, closure _, object k, object port)"
+      " object rv = Cyc_io_char_ready(data, port);
+        return_closcall1(data, k, rv); ")
+    (define (char-ready? . port)
+      (if (null? port)
+        (Cyc-char-ready? (current-input-port))
+        (Cyc-char-ready? (car port))))
     (define (peek-char . port)
       (if (null? port)
         (Cyc-peek-char (current-input-port))