44 lines
1.6 KiB
Markdown
44 lines
1.6 KiB
Markdown
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title = "`interface`"
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weight = 1
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Defines an interface for a hardware module (see section
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[5.13](fixme)). An
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interface is essentially a `struct`, but its components are restricted
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to those things that have a physical interpretation as wires in and out
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of a circuit. The types of fields in an interface are more likely to
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involve `Action`'s (see section
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[5.11](fixme)),
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which are typically interpreted as "enable signals" into a circuit. The
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fields of an interface are also known as *methods* (not to be confused
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with methods of a class, described in Sections
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[2.1](fixme) and
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[4.5](fixme)).
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```
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topDefn ::= interface typeId {tyVarId }= { { fieldDef ; }}
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```
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Example:
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```hs
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interface Stack a =
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push :: a -> Action
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pop :: Action
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top :: Maybe a
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```
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This describes a circuit that implements a stack (a LIFO) of items. This
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polymorphic definition does not specify the type of the contents of the
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stack, just that they have some type "`a`". Corresponding to the `push`
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method, the circuit will have input wires to carry a value of type
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"`a`", and a "push-enable" input wire that specifies when the value
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present on the input wires should be pushed on the stack. Corresponding
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to the `pop` component, the circuit will have a "pop-enable" input wire
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that specifies when a value should be popped off the stack.
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Corresponding to the `top` component, the circuit will have a set of
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output wires: if the stack is empty, the wires will represent the value
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`Nothing`, and if the stack is non-empty and $v$ is the value at the top
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of the stack, the wires will represent `Maybe` $v$.
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