Unhelpful error message when there is junk after rule

Created by: bnoordhuis

$ echo 'macro m { rule JUNK {} => {} }' | bin/sjs -s

/home/bnoordhuis/src/sweet.js/lib/sweet.js:90
                    throw err$1891;
                          ^
Error: ASSERT: Only delimiters can be exposed
    at assert$1917 (/home/bnoordhuis/src/sweet.js/lib/syntax.js:17:19)
    at Object.Syntax$1921.expose (/home/bnoordhuis/src/sweet.js/lib/syntax.js:83:13)
    at eval (eval at <anonymous> (/home/bnoordhuis/src/sweet.js/lib/scopedEval.js:16:69), <anonymous>:80:60)
    at step$623 (/home/bnoordhuis/src/sweet.js/lib/expander.js:1062:34)
    at enforest$442 (/home/bnoordhuis/src/sweet.js/lib/expander.js:1183:16)
    at expandToTermTree$448 (/home/bnoordhuis/src/sweet.js/lib/expander.js:1355:21)
    at expandTermTreeToFinal$450 (/home/bnoordhuis/src/sweet.js/lib/expander.js:1562:38)
    at /home/bnoordhuis/src/sweet.js/lib/expander.js:1615:20
    at Array.map (native)
    at Function._.map._.collect (/home/bnoordhuis/src/sweet.js/node_modules/underscore/underscore.js:95:56)

I was looking at how to fix that; is replacing the assert with a throwSyntaxError statement a reasonable thing to do?