In programming language theory, the qualification principle states that any semantically meaningful syntactic class may admit local definitions. In other words, it's possible to include a block in any syntactic class, provided that the phrases of that class specify some kind of computation.
A common examples for of this principle includes:
- block command -- a command containing a local declaration, which is used only for executing this command. In the following excerpt from a C program, <code>tmp</code> variable declared is local to the surrounding block command:
- block expression -- an expression containing a local declaration, which is used only for evaluating this expression. In the following excerpt from ML program, local declaration of <code>g</code> can be used only during evaluation of the following expression:
- block declaration is one containing a local declaration, the bindings produced by which are used only for elaborating the block declaration. In the following excerpt from ML program, local declaration of function <code>leap</code>, using an auxiliary function <code>multiple</code>:
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