Add directory management functions

This uses the POSIX API, so I don't know if it'll work in Windows (I
assume not. Sorry.)

libs/prelude/Prelude/File.idr

@@ -21,8 +21,13 @@ import IO
 data File : Type where
   FHandle : (p : Ptr) -> File
 
+||| A directory handle
+data Directory : Type where
+  DHandle : (p : Ptr) -> Directory
+
 -- Usage hints for erasure analysis
 %used FHandle p
+%used DHandle p
 
 ||| An error from a file operation
 -- This is built in idris_mkFileError() in rts/idris_stdfgn.c. Make sure
@@ -280,3 +285,46 @@ writeFile fn contents = do
      Right () <- fPutStr h contents        | Left err => pure (Left err)
      closeFile h
      pure (Right ())
+
+
+export
+dirOpen : (d : String) -> IO (Either FileError Directory)
+dirOpen d
+    = do dptr <- foreign FFI_C "idris_dirOpen" (String -> IO Ptr) d
+         if !(nullPtr dptr)
+            then do err <- getFileError
+                    pure (Left err)
+            else pure (Right (DHandle dptr))
+
+export
+dirClose : Directory -> IO ()
+dirClose (DHandle d) = foreign FFI_C "idris_dirClose" (Ptr -> IO ()) d
+
+export
+dirError : Directory -> IO Bool
+dirError (DHandle d)
+    = do err <- foreign FFI_C "idris_dirError" (Ptr -> IO Int) d
+         pure (not (err == 0))
+
+export
+dirEntry : Directory -> IO (Either FileError String)
+dirEntry (DHandle d)
+    = do fn <- foreign FFI_C "idris_nextDirEntry" (Ptr -> IO String) d
+         if !(dirError (DHandle d))
+            then pure (Left FileReadError)
+            else pure (Right fn)
+
+export
+createDir : String -> IO (Either FileError ())
+createDir d
+    = do ok <- foreign FFI_C "idris_mkdir" (String -> IO Int) d
+         if (ok == 0)
+            then pure (Right ())
+            else do err <- getFileError
+                    pure (Left err)
+
+export
+changeDir : String -> IO Bool
+changeDir dir 
+    = do ok <- foreign FFI_C "chdir" (String -> IO Int) dir
+         pure (ok == 0)

rts/idris_stdfgn.c

@@ -8,6 +8,7 @@
 #include <sys/stat.h>
 #include <stdio.h>
 #include <time.h>
+#include <dirent.h>
 
 #if defined(WIN32) || defined(__WIN32) || defined(__WIN32__)
 int win_fpoll(void* h);
@@ -59,6 +60,50 @@ int fileSize(void* h) {
     }
 }
 
+typedef struct {
+    DIR* dirptr;
+    int error;
+} DirInfo;
+
+void* idris_dirOpen(char* dname) {
+    DIR *d = opendir(dname);
+    if (d == NULL) {
+        return NULL;
+    } else {
+        DirInfo* di = malloc(sizeof(DirInfo));
+        di->dirptr = d;
+
+        return (void*)di;
+    }
+}
+
+void idris_dirClose(void* h) {
+    DirInfo* di = (DirInfo*)h;
+
+    closedir(di->dirptr);
+    free(di);
+}
+
+char* idris_nextDirEntry(void* h) {
+    DirInfo* di = (DirInfo*)h;
+    struct dirent* de = readdir(di->dirptr);
+
+    if (de == NULL) {
+        di->error = -1;
+        return NULL;
+    } else {
+        return de->d_name;
+    }
+}
+
+int idris_mkdir(char* dname) {
+    return mkdir(dname, S_IRWXU | S_IRGRP | S_IROTH);
+}
+
+int idris_dirError(void *dptr) {
+    return ((DirInfo*)dptr)->error;
+}
+
 int idris_writeStr(void* h, char* str) {
     FILE* f = (FILE*)h;
     if (fputs(str, f) >= 0) {

rts/idris_stdfgn.h

@@ -15,6 +15,17 @@ int fileError(void* h);
 // Returns a negative number if not a file (e.g. directory or device)
 int fileSize(void* h);
 
+void* idris_dirOpen(char* dname);
+void idris_dirClose(void* h);
+char* idris_nextDirEntry(void* h);
+
+// Create a directory; return 0 on success or -1 on failure
+int idris_mkdir(char* dname);
+
+// Return 0 if ok, or -1 if there was an error with the given directory
+// (like ferror)
+int idris_dirError(void *dptr);
+
 // return 0 on success
 int idris_writeStr(void*h, char* str);
 // construct a file error structure (see Prelude.File) from errno