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call-with-input-file*
call-with-output-file*
build-relative-path
build-absolute-path

 (require mzlib/file)

The mzlib/file library mostly re-exports from scheme/file:

find-relative-path
explode-path
normalize-path
filename-extension
file-name-from-path
path-only
delete-directory/files
copy-directory/files
make-directory*
make-temporary-file
get-preference
put-preferences
fold-files
find-files
pathlist-closure

(call-with-input-file* file proc [mode])  any
  file : path-string?
  proc : (input-port? -> any)
  mode : (one-of/c 'text 'binary) = 'binary
(call-with-output-file* file    
  proc    
  [mode    
  exists])  any
  file : path-string?
  proc : (output-port? -> any)
  mode : (one-of/c 'text 'binary) = 'binary
  exists : 
(one-of/c 'error 'append 'update
          'replace 'truncate 'truncate/replace)
   = 'error
Like call-with-input-fileand call-with-output-file, except that the opened port is closed if control escapes from the body of proc.

(build-relative-path base sub ...)  (and/c path? relative-path?)
  base : 
(or/c path-string?
      (one-of/c 'up 'same))
  sub : 
(or/c (and/c path-string?
             relative-path?)
      (one-of/c 'up 'same))
(build-absolute-path base sub ...)  (and/c path? absolute-path?)
  base : 
(or/c (and/c path-string?
             (not/c relative-path?))
      (one-of/c 'up 'same))
  sub : 
(or/c (and/c path-string?
             (not/c complete-path?))
      (one-of/c 'up 'same))
Like build-path, but with extra constraints to ensure a relative or absolute result.