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authorBjörn Gustavsson <[email protected]>2016-03-01 06:23:36 +0100
committerBjörn Gustavsson <[email protected]>2016-03-01 13:59:22 +0100
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Generalize bit string comprehensions
The expression in a bit string comprehension is limited to a literal bit string expression. That is, the following code is legal: << <<X>> || X <- List >> but not this code: << foo(X) || X <- List >> The limitation is annoying. For one thing, tools that transform the abstract format must be careful not to produce code such as: << begin %% Some instrumentation code. <<X>> end || X <- List >> One reason for the limitation could be that we'll get reduce/reduce conflicts if we try to allow an arbitrary expression in a bit string comprehension: binary_comprehension -> '<<' expr '||' lc_exprs '>>' : {bc,?anno('$1'),'$2','$4'}. Unfortunately, there does not seem to be an easy way to work around that problem. The best we can do is to allow 'expr_max' expressions (as in the binary syntax): binary_comprehension -> '<<' expr_max '||' lc_exprs '>>' : {bc,?anno('$1'),'$2','$4'}. That will work, but functions calls must be enclosed in parentheses: << (foo(X)) || X <- List >>
Diffstat (limited to 'system/doc/reference_manual/expressions.xml')
-rw-r--r--system/doc/reference_manual/expressions.xml8
1 files changed, 5 insertions, 3 deletions
diff --git a/system/doc/reference_manual/expressions.xml b/system/doc/reference_manual/expressions.xml
index e98fcbcbb9..75486488e9 100644
--- a/system/doc/reference_manual/expressions.xml
+++ b/system/doc/reference_manual/expressions.xml
@@ -1556,9 +1556,11 @@ end</pre>
<p>Bit string comprehensions are written with
the following syntax:</p>
<pre>
-&lt;&lt; BitString || Qualifier1,...,QualifierN &gt;&gt;</pre>
- <p>Here, <c>BitString</c> is a bit string expression and each
- <c>Qualifier</c> is either a generator, a bit string generator or a filter.</p>
+&lt;&lt; BitStringExpr || Qualifier1,...,QualifierN &gt;&gt;</pre>
+ <p><c>BitStringExpr</c> is an expression that evalutes to a bit
+ string. If <c>BitStringExpr</c> is a function call, it must be
+ enclosed in parentheses. Each <c>Qualifier</c> is either a
+ generator, a bit string generator or a filter.</p>
<list type="bulleted">
<item>A <em>generator</em> is written as: <br></br>
&nbsp;&nbsp;<c><![CDATA[Pattern <- ListExpr]]></c>. <br></br>