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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
commit205405f0bf1d2fa37d4c8170c11689a2937f5d9c (patch)
treea55b2a94a43ecf521db5c06a41be2af0a0eda44b /lib/stdlib/src/erl_parse.yrl
parent156aea75186fe9de64b87c2c6919db9abf4a0d60 (diff)
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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 'lib/stdlib/src/erl_parse.yrl')
-rw-r--r--lib/stdlib/src/erl_parse.yrl2
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/stdlib/src/erl_parse.yrl b/lib/stdlib/src/erl_parse.yrl
index b1c574ea60..6f8e5e8449 100644
--- a/lib/stdlib/src/erl_parse.yrl
+++ b/lib/stdlib/src/erl_parse.yrl
@@ -311,7 +311,7 @@ bit_size_expr -> expr_max : '$1'.
list_comprehension -> '[' expr '||' lc_exprs ']' :
{lc,?anno('$1'),'$2','$4'}.
-binary_comprehension -> '<<' binary '||' lc_exprs '>>' :
+binary_comprehension -> '<<' expr_max '||' lc_exprs '>>' :
{bc,?anno('$1'),'$2','$4'}.
lc_exprs -> lc_expr : ['$1'].
lc_exprs -> lc_expr ',' lc_exprs : ['$1'|'$3'].