Yes, it could be extracted to a separate module, but package
github.com/cosmos72/gomacro/ast2 already has very few dependencies.
In particular, it does *not* depend on the Go interpreter
github.com/cosmos72/gomacro/fast
The integer arguments are simple:
`y.Get(0)` means "get the first (index = 0 ) child node of y"
`y.Get(1)` means "get the second (index = 1) child node of y"
and so on.
The interface `ast2.Ast` also has methods to query the number of children,
and to modify the AST:
```
type Ast interface {
Interface() interface{}
Op() token.Token
Size() int
Get(i int) Ast
Set(i int, child Ast)
New() Ast // returns a copy of Ast. the children are not copied
}
```
On Wednesday, October 14, 2020 at 8:06:57 PM UTC+2 [email protected] wrote:
> Hi Max,
>
> Great answer, thank you! Exactly what I was looking for in terms of a
> fluid api, no need for parsing the selectors.
>
> The API is not quite suitable for public consumption. I feel this could be
> a great success if extracted into its own module.
> Could you kindly clarify what the meaning of the int parameters is, i.e.
> is there a general rule or does it depend on the function?
>
> I‘ll play a bit with it and will comment on GH if ok.
>
> Much appreciated,
> Andi
>
> On Wednesday, October 14, 2020 at 6:09:08 PM UTC+2 Max wrote:
>
>> I can only agree, traversing or navigating Go AST is cumbersome for at
>> least two reasons:
>> 1. each type has its own fields - no uniform API is available
>> 2. you often need type assertions on fields because they have interface
>> type instead of concrete type
>>
>> I developed a wrapper around them to mitigate these problems for my Go
>> interpreter https://github.com/cosmos72/gomacro
>> If you are interested, it is the package
>> https://github.com/cosmos72/gomacro/tree/master/ast2
>>
>> You may find it helps by providing an uniform API and removing the need
>> for type assertions, but it still requires compile-time code,
>> not CSS-style strings that can be created at runtime.
>>
>> A quick example: this uses plain go/ast
>> ```
>> package main
>> import (
>> "fmt"
>> "go/ast"
>> "go/parser"
>> )
>> func main() {
>> x, _ := parser.ParseExpr("foo[1 + 2 * 3]")
>> // we want to extract the "3"
>> var three string =
>> x.(*ast.IndexExpr).Index.(*ast.BinaryExpr).Y.(*ast.BinaryExpr).Y.(*ast.BasicLit).Value
>> fmt.Printf("%s\n", three) // prints 3
>> }
>> ```
>> while this is the equivalent using github.com/cosmos72/gomacro/ast2
>> ```
>> package main
>> import (
>> "fmt"
>> "go/ast"
>> "go/parser"
>> "github.com/cosmos72/gomacro/ast2"
>> )
>> func main() {
>> x, _ := parser.ParseExpr("foo[1 + 2 * 3]")
>> y := ast2.AnyToAst(x, nil) // wrap the existing AST. does not
>> allocate memory.
>>
>> ythree := y.Get(1).Get(1).Get(1) // extract the "3" as ast2.Node
>>
>> // now unwrap it, getting the *ast.BasicLit and the Value inside it
>> var three string = ast2.ToBasicLit(ythree).Value
>> fmt.Printf("%s\n", three) // prints 3
>> }
>> ```
>>
>> On Tuesday, October 13, 2020 at 9:37:21 AM UTC+2 [email protected] wrote:
>>
>>> Good morning.
>>>
>>> I've recently found myself writing a code generator for dynamic
>>> interface composition at runtime. It became ugly and I had to pass in quite
>>> a number of parameters that should have been available from reading the
>>> source code.
>>>
>>> In a second attempt I've reimplemented the generator using stringer-like
>>> AST handling. It worked well but was cumbersome to code.
>>>
>>> Now an idea surfaced: wouldn't it make sense to implement a selector
>>> interface on top of the golang AST, something like CSS or JQ selectors but
>>> targeted at the go language constructs? I've stumbled across Guru but it
>>> does seem to target a slightly different use case.
>>>
>>> Is anybody aware of such a selector lib/module or does the idea even
>>> sound interesting?
>>>
>>> Cheers,
>>> Andi
>>>
>>
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