type_aliases.carp

; type aliases as a macro-writing macro
;
; this will enable you to write, for instance:
;   (type-alias Foo Int)
;   (def x (the-Foo 1))
; and thus make foo an alias for Int.
; the syntax is not quite as convenient as it could be,
; and if you have a better idea for an API I encourage
; you to experiment with it; i found this problem to
; be extremely gratifying.

; a worker function for our macro: it will piece
; together the macro that the user will then call,
; `the-<typename>`.
(defndynamic type-alias-helper [name aliased]
  ; we build a macro head similarly to what we would do
  ; if we emitted a function here.
  (list 'defmacro (Symbol.concat ['the- name]) (array 'x)
    ; this is a little involved. listing `list` and quoting
    ; `quote` might seem a little outlandish, but what we
    ; want the body of the macro to be is basically
    ; `(list 'the '<typename> <arg>)`, which requires us
    ; to do a little bit of meta-meta-programming.
    (list 'list (list 'quote 'the) (list 'quote aliased) 'x)))

; the macro just passes everything to the worker function
; as is.
(defmacro type-alias [name aliased]
  (type-alias-helper name aliased))