Hey @julianhyde if you could take a look at what I've done here: https://github.com/apache/calcite/pull/3093/files#diff-9e0f6e9c4d4f86444e48290b1e613ba700c0854cd614bee4a1912ccb75aed272R1203

@tjbanghart helped me take a look at your suggestion too with using some Supplier

public static final Object safe(Supplier r) {
	try {
	 return r.get();
	} catch (RuntimeException e) {
	return null;
	}
}

but the typing isn't so compatible with Expressions.lambda, which expects a subclass of Function.class and we haven't figured it out

In future, please use the jira case number in the first commit message and in the title of the PR. (Yes, that requires that you log a jira case before starting work on the bug. That is a good thing.)

(Too late to change the first commit message now. That would destroy history.)

I think Expressions.lambda(BlockStatement, Iterable) will work. If there are zero parameters deduceType will return Function0.class, which is equivalent to java.lang.Supplier. (This code was written before Supplier was added in JDK 8.)

BlockStatement will probably contain a single statement, a GotoStatement with your expression, which you will create using Expressions.return_.

I'm still in the middle of cleaning up the PR, thanks for reviewing @zoudan

Do you have any thoughts on SqlSyntax.SPECIAL?
It should be SPECIAL, but the operator table lookup currently doesn't look for SPECIAL syntax functions, so that was just a temporary workaround.

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3 Bugs
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0 Security Hotspots
63 Code Smells

83.6% Coverage
14.9% Duplication

@olivrlee Can you review my additional commits? I was able to solve the SPECIAL issue

I did take a look but communicated to Julian offline*