File: tysubst.doc

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\DOC tysubst

\TYPE {tysubst : (hol_type * hol_type) list -> hol_type -> hol_type}

\DESCRIBE
The call {tysubst [ty1',ty1; ... ; tyn',tyn] ty} will systematically traverse 
the type {ty} and replace the topmost instances of any {tyi} encountered with 
the corresponding {tyi'}. In the (usual) case where all the {tyi} are type 
variables, this is the same as {type_subst}, but also works when they are not.

\FAILURE
Never fails. If several {tyi} are the same, the first one in the list will be
used to determine the substitution.

\EXAMPLE
{
  # tysubst [`:num`,`:A`; `:bool`,`:B`] `:A->(B)list->A#B#C`;;            
  val it : hol_type = `:num->(bool)list->num#bool#C`
  # tysubst [`:A`,`:(num)list`] `:num->(num)list->(num)list`;;
  val it : hol_type = `:num->A->A`
}

\SEEALSO
inst, tysubst.

\ENDDOC