How can we make it easier to experiment with the compiler?

[Basile B.]

On Monday, 24 May 2021 at 19:42:00 UTC, user1234 wrote:
> Eventually what could be done for the biggest methods of 
> visitors is to extract parts of the content to several 
> **non-nested** free functions, so that no more low level 
> implementation details, like control loops, are visible and 
> instead you just see do_this; do_that; with just a few, 
> nzzcessarily unavoidable, flow statements.

I've had the opportunity to do quch a refact yesterday in styx. 
It makes things very clear, for example the expression semantic 
for binary assign exps :

```d
override void visit(BinAssExpressionAstNode node)
{
     processBinaryOperands(node);
     if (tryRewritingToOperatorOverload(node, [node.left, 
node.right]))
         return;
     if (tryToSetLengthExp(node))
         return;
     if (checkIfInvalidEnumSetOp(node))
         return;
     if (checkPtrArithmeticOp(node))
         return;
     ensureAssignedParamIsLvalue(node);
     tryOneWayAssImplicitConv(node);
     checkIfAssignable(node.left);
}
```

or for binary exps that are not assign and not cmp:

```d
override void visit(BinaryExpressionAstNode node)
{
     processBinaryOperands(node);
     if (tryRewritingToOperatorOverload(node, [node.left, 
node.right]))
         return;
     if (checkIfInvalidEnumSetOp(node))
         return;
     if (checkPtrArithmeticOp(node))
         return;
     tryTwoWaysBinaryImplicitConv(node);
}
```

It was like 200 lines before.