Update procedure exact? to built-in

Signed-off-by: yamacir-kit <[email protected]>

README.md

@@ -99,7 +99,7 @@ Procedures for each standard are provided by the following R7RS-style libraries:
 cmake -B build -DCMAKE_BUILD_TYPE=Release
 cd build
 make package
-sudo apt install build/meevax_0.5.6_amd64.deb
+sudo apt install build/meevax_0.5.7_amd64.deb
 ```
 
 or
@@ -131,9 +131,9 @@ sudo rm -rf /usr/local/share/meevax
 
 | Target Name | Description
 |-------------|-------------
-| `all`       | Build shared-library `libmeevax.0.5.6.so` and executable `meevax`
+| `all`       | Build shared-library `libmeevax.0.5.7.so` and executable `meevax`
 | `test`      | Test executable `meevax`
-| `package`   | Generate debian package `meevax_0.5.6_amd64.deb`
+| `package`   | Generate debian package `meevax_0.5.7_amd64.deb`
 | `install`   | Copy files into `/usr/local` directly
 
 ## Usage

VERSION

@@ -1 +1 @@
-0.5.6
+0.5.7

basis/r4rs.ss

@@ -51,6 +51,7 @@
                 real?
                 rational?
                 integer?
+                exact?
                 = < > <= >=
                 + * - /
                 abs
@@ -331,15 +332,6 @@
                        (car alist)
                        (assoc (cdr alist)))))))
 
-         (define (exact? z)
-           (define (exact-complex? x)
-             (and (imaginary? x)
-                  (exact? (real-part x))
-                  (exact? (imag-part x))))
-           (or (exact-complex? z)
-               (ratio? z)
-               (exact-integer? z)))
-
          (define (inexact? z)
            (define (inexact-complex? x)
              (and (imaginary? x)