From 205405f0bf1d2fa37d4c8170c11689a2937f5d9c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 1 Mar 2016 06:23:36 +0100 Subject: 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 <- 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. <> 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 >> --- lib/stdlib/src/erl_parse.yrl | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib/stdlib/src') 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']. -- cgit v1.2.3