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--- language:langs:refine [2024/08/11 10:21] – rajit
+++ language:langs:refine [2025/07/21 19:47] (current) – [Multiple refinement options] rajit
@@ Line 73: / Line 73: @@
 ===== Nested refinements =====
+Since ''refine { ... }'' blocks contain normal ACT statements, they can also include refine blocks within them.
+Hence, you can say:
+<code act>
+refine {
+    inst i1;
+    chp { ... }
+    refine { inst i2; }
+}
+</code>
+When ACT selects the outer refinement block for the process, it decrements the refinement level before proceeding; the level is restored at the end of the refinement block. Hence, if  ''-ref=1'' were specified, then
+the block:
+<code act>
+  inst i1;
+  chp { ... }
+  refine { inst i2; }
+</code>
+would be processed with the refinement level set to zero; hence, the ''chp { ... }'' body would be selected, and
+not the nested refinement. To replace the CHP with the nested refinement block, use ''-ref=2''. Note that in both cases the instance ''i1'' would be processed.
 ===== Multiple refinement options =====
+While the nested refinement approach works nicely when designs are recursively refined, it may not
+be suitable for transformations where an existing refinement block needs to be completely replaced.
+ACT has a mechanism to support this in the following manner:
+<code act>
+refine {
+    inst i1;
+    chp { ... }
+}
+refine<2> {
+    inst j1;
+    prs { ... }
+}
+</code>
+In this case, the ''refine<2> { ... }'' block behaves as ''refine { refine { ... } }''. In other words, when ''-ref=2'' is specified,
+instance ''i1'' as well as ''j1'' will be created. Furthermore, the refinement option will eliminate the ''chp { ... }'' block from the first level refinement, as this has now been replaced with the second level refinement.
+===== Refinement overrides =====
+Sometimes a refinement body needs to [[language:impl#overrides|override]] types. To support this, refinement bodies can be accompanied by refinement overrides. These are overrides that are only applied when the refinement is used.
+The syntax for providing refinement overrides is below:
+<code act>
+refine<2>  +{ e1of2 l; } {
+       inst1 i1;
+       ...
+ }
+</code>
+This will apply the refinement override for ''l'' when this particular refinement body is selected.