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Aucbvax.5006 fa.editor-p utzoo!decvax!ucbvax!editor-people Sat Nov 7 00:25:37 1981 Strong typing is bad for you >From RMS@MIT-AI Fri Nov 6 23:53:41 1981 The type checking of PASCAL is detrimental to extensibility. Every declaration about an external function or variable is a duplicate redundant piece of information which increases the number of different places which must be edited in order to make a particular change. In some of those places, the code may need to be changed anyway, but probably NOT in all of them.

In addition, requiring type declarations makes it hard for the user to write a large class of generic functions including MAPCAR and MEMBER. MAPCAR calls a user-supplied function over and over and makes a list of the values. This is not even imaginable unless the language has a list structure data type which allows any type of data for the elements. MEMBER searches a list for something that matches a specified value. The code for MEMBER can be the same no matter what type the elements are; but a typed language would force the user to declare that type, thus restricting any single MEMBER-like function to working on only one data type. MAPCAR and MEMBER are built-in in Maclisp dialects, but the class of functions which would run into the same problem is infinite.

Allowing overloading does not solve this problem. I do not want to be permitted to write a dozen definitions for MEMBER, identical except for declarations. I want to write only one.

If type checking and declarations are optional, then they can be valuable. If mandatory, as in most of the obsolete batch languages including PASCAL and Ada, they are a screw.

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