How to Implement Recursive data type?

[Geo-7]

NOTICE: I've read this post #69 anyway I want to Implement this with current unsafe features
I want to Implement abstract syntax tree in mojo, so far no luck,
Something simple as this in C :
https://github.com/orangeduck/mpc/blob/master/mpc.h#L291

struct ast {
  char *tag;
  char *contents;
  int children_num;
  struct ast** children;
}

I have tried two solution
First: I could not implement add_chlid getting error: candidate not viable: method argument #1 cannot bind generic !mlirtype to memory-only type 'AST'

@value
@register_passable("trivial")
struct UnsafeString:
    var data: Pointer[Int8]
    var len: Int

    fn __init__(str: StringLiteral) -> UnsafeString:
        let l = str.__len__()
        let s = String(str)
        let p = Pointer[Int8].alloc(l)
        for i in range(l):
            p.store(i, s._buffer[i])
        return UnsafeString(p, l)

    fn to_string(self) -> String:
        let s = String(self.data, self.len)
        return s


struct AST:
    var tag: UnsafeString
    var content: UnsafeString
    var child_no: Int
    var children: Pointer[AST]

    fn __init__(
        inout self,
        tag: UnsafeString = "ILLEGAL",
        content: UnsafeString = "un",
        child_no: Int = 0,
    ):
        self.tag = tag
        self.content = content
        self.child_no = child_no
        self.children = Pointer[AST].alloc(child_no * 2)

    fn add_child(inout self, owned other: Self):
        self.children.store(0, other)


fn main():
    print("AST Started")
    var child1 = AST()
    var child2 = AST()
    var parent = AST()

Second error: no matching function in call to 'init':
var child1 = AST()
~~~^~
candidate not viable: callee expects at least 1 argument, but 0 were specified

@value
@register_passable("trivial")
struct UnsafeString:
    var data: Pointer[Int8]
    var len: Int

    fn __init__(str: StringLiteral) -> UnsafeString:
        let l = str.__len__()
        let s = String(str)
        let p = Pointer[Int8].alloc(l)
        for i in range(l):
            p.store(i, s._buffer[i])
        return UnsafeString(p, l)

    fn to_string(self) -> String:
        let s = String(self.data, self.len)
        return s


@value
@register_passable("trivial")
struct AST:
    var tag: UnsafeString
    var content: UnsafeString
    var child_no: Int
    var children: Pointer[AST]

    fn __init__(
        inout self,
        tag: UnsafeString = "ILLEGAL",
        content: UnsafeString = "un",
        child_no: Int = 0,
    ) -> AST:
        self.tag = tag
        self.content = content
        self.child_no = child_no
        self.children = Pointer[AST].alloc(child_no * 2)
        return self

    fn add_child(inout self, owned other: Self):
        self.children.store(0, other)


fn main():
    print("AST Started")
    var child1 = AST()
    var child2 = AST()
    var parent = AST()

is there a way to use memory.unsafe.bitcast (or anything else) to solve this ?

[rarebreed]

I believe you still need a self parameter as the first param to __init__ in your UnsafeString. Not sure if that is the problem though (havent tried to run your code).

[Geo-7]

No, that would not work, I also should remove self from AST.init in my second example

[Geo-7]

I've changed the second example but I'm getting new error:

error: LLVM Translation failed for operation: builtin.unrealized_conversion_cast
        var tmp_ast = AST(tag, content, child_no, children)
                         ^
/home/fake_user/Projects/Mojo/ast/src/nast.mojo:34:26: note: see current operation: %45 = "builtin.unrealized_conversion_cast"(%44) : (!llvm.struct<(struct<(ptr<i8>, i64)>, struct<(ptr<i8>, i64)>, i64, ptr<struct<(struct<(ptr<i8>, i64)>, struct<(ptr<i8>, i64)>, i64, ptr)>>)>) -> !pop.struct<struct<pointer<scalar<si8>>, index>, struct<pointer<scalar<si8>>, index>, index, pointer<struct<struct<pointer<scalar<si8>>, index>, struct<pointer<scalar<si8>>, index>, index, pointer<scalar<invalid>>>>>
/home/fake_user/.modular/pkg/packages.modular.com_mojo/bin/mojo: error: Failed to materialize symbols: { (exec, { main }) } (from the layer: failed to lower module to LLVM IR for archive compilation)

@value
@register_passable("trivial")
struct UnsafeString:
    var data: Pointer[Int8]
    var len: Int

    fn __init__(str: StringLiteral) -> UnsafeString:
        let l = str.__len__()
        let s = String(str)
        let p = Pointer[Int8].alloc(l)
        for i in range(l):
            p.store(i, s._buffer[i])
        return UnsafeString(p, l)

    fn to_string(self) -> String:
        let s = String(self.data, self.len)
        return s


@value
@register_passable("trivial")
struct AST:
    var tag: UnsafeString
    var content: UnsafeString
    var child_no: Int
    var children: Pointer[AST]

    fn __init__(
        tag: UnsafeString = "ILLEGAL",
        content: UnsafeString = "un",
        child_no: Int = 0,
    ) -> AST:
        var children = Pointer[AST].alloc(child_no * 2)
        var tmp_ast = AST(tag, content, child_no, children)
        return tmp_ast

    fn add_child(inout self, owned other: Self):
        self.children.store(0, other)


fn main():
    print("AST Started")
    var child1 = AST()
    var child2 = AST()
    var parent = AST("Ident", "parent", 2)
    parent.add_child(child1)