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The defun statement is the second most commonly used defining statement in PLOT, hence an abbreviated name is justified. It defines a method for a function. The definition appears in the current scope, which can be local or global.
The defun statement first defines a function, unless the name is already defined in the current scope. The name must be defined as a function or an operator. Note that if the current scope is a local scope, this definition must be directly in the current scope, not inherited from an enclosing scope. defun will never add a method to a function inherited from a containing scope. Note that if the current scope is a module, the definition can be imported from another module. defun can add a method to an imported function.
Next, the defun statement creates a method and adds it to the function or operator. The value of the statement as a whole is the function or operator.
The syntax of the defun statement is as follows:
defmacro defun ?:method-head [ ?:annotations ] ?:block => ...
The following annotations are predefined for defun:
| sealed | This method must always be the most specific when applicable. The compiler can optimize based on the knowledge that this method cannot be overridden by a more specific method. |
| subsumptive | This method has equivalent effect to any more specific method when both are applicable. This enables certain special cases of compiler optimization. |
| intrinsic(name) | The compiler has special knowledge of this method under the specified name. The name is optional and defaults to the name of the function. |
An example usage of subsumptive methods:
defun (x is simple-name) = (y is anything) : subsumptive x eq y defun (x is anything) = (y is simple-name) : subsumptive x eq yThis says that = on simple-names is always eq, and nothing other than a simple-name can be = to a simple-name, without considering what other methods might be defined for =. The parentheses are unnecessary, because of operator precedence, but probably improve readability.
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