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--- language:types2 [2024/07/18 16:28] – [Macros and Functions] rajit
+++ language:types2 [2024/10/24 10:28] (current) – [Functions] rajit
@@ Line 160: / Line 160: @@
 adder and five-bit adder.
+==== Default parameters ====
-===== Direction flags and user-defined types =====
+When defining complex user-defined types with many parameters, it can be useful to have
+default parameter values. ACT has syntax to support default parameter values for trailing
+parameters in a template definition.
+<code act>
+template <pint N; pbool active_high = true>
+defproc driver(bool? inp; bool! outp)
+{
+  bool sig;
+  prs {
+    inp => sig-
+  }
+  [active_high -> prs { sig => outp- }
+  [] else -> sig = outp;
+  ]
+}
+</code>
+(Note: this is not a real signal driver, but the idea here is the you have a parameterized
+driver that can drive a fanout of ''N'' gates.) This definition has a default value for the
+''active_high'' parameter as ''true''.  So an instance
+<code act>
+driver<4> x;
+</code>
+will have four production rules:
+<code act>
+ x.inp -> sig-
+~x.inp -> sig+
+ sig -> x.outp-
+~sig -> x.outp+
+</code>
+However, this behavior can be changed by using:
+<code act>
+driver<4,false> x;
+</code>
+In this case, ''sig'' will be connected to ''x.outp''.
+Note that ACT is very strict about type-checking; so, for example, ''driver<4>'' and ''driver<4,true>'' are //not// treated as the same type even though the default parameter value for the second template parameter is ''true''.
+===== Direction flags  =====
@@ Line 205: / Line 243: @@
 is detailed in the section on connections.
-===== Macros and Functions =====
+===== Macros and Functions within User-defined types =====
 User-defined types support additional methods (beyond the special ones for channels and data types).
@@ Line 216: / Line 254: @@
 ==== Functions ====
+=== Operator overloading ===