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+title = "`type`"
+weight = 1
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+
+Defines a type synonym. These are used purely for readability, *i.e.,* a
+type synonym can always be "expanded out" to its definition at any time.
+
+```
+topDefn ::= type typeId {tyVarId }= type
+```
+
+Examples:
+
+```hs
+type Byte     = Bit 8
+type Word     = Bit 16
+type LongWord = Bit 32
+```
+
+These provide commonly used names for certain bit lengths. In a
+specification of a processor:
+
+```hs
+data RegName = R0 | R1 | ... | R31
+type Rdest = RegName
+type Rsrc = RegName
+data ArithInstr = Add Rdest Rsrc Rsrc
+                | Sub Rdest Rsrc Rsrc
+```
+
+the last two lines suggest the roles of the registers in the
+instructions, and is more readable than:
+
+```hs
+data ArithInstr = Add RegName RegName RegName
+                | Sub RegName RegName RegName
+```