Macro Cond

Author: iwillspeak

spec/conditions.scm

@@ -18,28 +18,18 @@
         "world"
         -2))
 
-(define-syntax my-cond
-    (syntax-rules (else)
-        ((cond (else e ...))   (begin e ...))
-        ((cond (test e e1 ...))
-            (if test
-                (begin e e1 ...)))
-        ((cond (test e e1 ...) c ...)
-            (if test
-                (begin e e1 ...)
-                (my-cond c ...)))))
 (display
-    (my-cond
+    (cond
         (#f 'false)
         (#t 'true)
         (else 'fail)))
 (display
-    (my-cond
+    (cond
         (#f 'false)
         (#t 'true)))
 (display
-    (my-cond
+    (cond
         (else 'ok)))
 (display
-    (my-cond 
+    (cond 
         (#f 'fail)))

src/Feersum/Bind.fs

@@ -627,8 +627,6 @@ and private bindForm ctx (form: AstNode list) node =
             |> Result.map (BinderCtx.importLibrary ctx >> BoundExpr.Import)
             |> ResultEx.okOr BoundExpr.Error)
         |> BoundExpr.Seq
-    | { Kind = AstNodeKind.Ident("cond") }::body ->
-        unimpl "Condition expressions not yet implemented"
     | { Kind = AstNodeKind.Ident("case") }::body ->
         unimpl "Case expressions not yet implemented"
     | head::rest -> 

src/Feersum/Builtins.fs

@@ -210,6 +210,7 @@ module private BuiltinMacros =
 
     /// Builtin `or` Macro
     let private macroOr =
+        // TODO: re-write this when proper hygene is supported.
         "(syntax-rules ()
             ((or) #f)
             ((or test) test)
@@ -238,11 +239,26 @@ module private BuiltinMacros =
                     expr1 ...))))"
         |> parseBuiltinMacro "unless"
 
+    let private macroCond =
+        // TODO: This `cond` implementation doesn't support the `=>` 'pipe' form
+        //       of the macro yet. This is because we're waiting for hygene
+        //       support like `or`.
+        "(syntax-rules (else)
+            ((cond (else e ...))   (begin e ...))
+            ((cond (test e e1 ...))
+                (if test
+                    (begin e e1 ...)))
+            ((cond (test e e1 ...) c ...)
+                (if test
+                    (begin e e1 ...)
+                    (cond c ...))))"
+        |> parseBuiltinMacro "cond"
+
     /// The list of builtin macros
     let coreMacros =
         { LibraryName = ["scheme";"base"]
         ; Exports =
-            [ macroAnd ; macroOr; macroWhen; macroUnless ]
+            [ macroAnd ; macroOr; macroWhen; macroUnless; macroCond ]
             |> List.map (fun m -> (m.Name, StorageRef.Macro(m))) }
 
 // ------------------------ Public Builtins API --------------------------------