[[project @ 2001-06-11 14:15:32 by simonpj]
simonpj**20010611141532
document data types with no constructors
] {
hunk ./ghc/docs/users_guide/glasgow_exts.sgml 98
+
+ Data types with no constructors
+
+ See .
+
+
+
hunk ./ghc/docs/users_guide/glasgow_exts.sgml 425
+
+Data types with no constructors
+
+With the
+
+ data S -- S :: *
+ data T a -- T :: * -> *
+
+Syntactically, the declaration lacks the "= constrs" part. The
+type can be parameterised, but only over ordinary types, of kind *; since
+Haskell does not have kind signatures, you cannot parameterise over higher-kinded
+types.
+
+Such data types have only one value, namely bottom.
+Nevertheless, they can be useful when defining "phantom types".
+
+
}