pipa-lang 1.0.0-alpha.1

A tiny template language
Documentation 
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// SPDX-FileCopyrightText: Copyright 2026 olav@occy.org
// SPDX-License-Identifier: MPL-2.0

use crate::lang::adapter::Adapter;
use crate::lang::args::eval_args;
use crate::lang::arity::Arity;
use crate::lang::arity::assert_func_arity;
use crate::lang::error::Error;
use crate::lang::machine::Machine;
use crate::lang::node::Node;
use crate::value::Value;

pub(crate) fn prepend(
    adapter: &impl Adapter,
    machine: &mut Machine<'_>,
    stdin: Option<&Value>,
    node: Node,
) -> Result<Value, Error> {
    assert_func_arity(adapter, machine, stdin, &node, &Arity::new(2))?;

    let mut node = eval_args(adapter, machine, stdin, node)?;
    let mut head = node.pop().flatten().unwrap_or_default();
    let tail = node.pop().flatten().unwrap_or_default();
    let tail = tail.into_other(&head);
    let tail = tail.with_meta("internal-insert", "prepend");

    head.fold(tail);
    Ok(head)
}