Abstract Virtual Machine for execution of end-user logic
It optimizes the code & include a more general "query planner"
The execution is split in 3 "phases":
1- AST formation
Generate the AST (that could be invalid according to the semantics).
This step is outside the [vm] and can be done, for example, by the SQL layer.
Use [dsl] to build the [expr:Expr] that build the AST.
2- AST validation
Calling [eval::optimize] verify the code has the correct semantics (ie: It checks types, schemas, functions are valid, etc.), and "desugar" the code in a more optimal form for later execution.
This build [expr::Expr] that is what could be stored in the database, ie: Is like bytecode.
3- Execution
Run the AST build from [expr::Expr]. It assumes is correct.