flesh/src/func.rs

/* relish: versatile lisp shell
 * Copyright (C) 2021 Aidan Hahn
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

use std::boxed::Box;
use std::collections::HashMap;
use crate::cell::{Ctr, Cell, Type};
use crate::vars::{VTable};
use crate::eval::eval;

// Standardized function signature for stdlib functions
pub type Operation = fn(Box<Cell>, Box<VTable>, Box<FTable>) -> Box<Cell>;
pub type FTable = HashMap<String, Function>;

/* Function Args
 * If Lazy, is an integer denoting number of args
 * If Strict, is a list of Ctrs (with no wrapped values) denoting arg type.
 */
pub enum Args {
    // signed: -1 denotes infinite args
    Lazy(i128),
    Strict(Vec<Type>)
}

// function which does not need args checked
pub struct Function {
    pub function: Operation,
    pub name: String,
    pub times_called: u128,
    pub args: Args,

    // dont fail on undefined symbol (passed to eval)
    pub loose_syms: bool,

    // dont evaluate args at all. leave that to the function
    pub eval_lazy: bool
}

impl Function {
    /* call
     * routine is called by eval when a function call is detected
     */
    pub fn call_function (
        &mut self,
        args: Box<cell>,
        vars: Box<VTable>,
        funcs: Box<FTable>
    ) -> Result<Box<Cell>, String> {
        let mut n_args = args;
        if !self.eval_lazy {
            match eval(args, vars, funcs, self.loose_syms) {
                Ok(box_cell) => n_args = box_cell,
                Err(s) => return Err(
                    format!(
                        "error evaluating args to {}: {}",
                        func.name,
                        s
                    )
                )
            }
        }

        let mut passes = false;
        match self.args {
            Args::Lazy(num) => {
                if num < 0 {
                    passes = true
                }

                if !(num == (args.len() - 1)) {
                    return Err(format!("expected {} args in call to {}", num, self.name))
                }
            },

            Args::Strict(arg_types) => {
                let idx: usize = 0;
                passes = args.circuit(|c: Ctr| {
                    if idx >= arg_types.len() {
                        return false;
                    }

                    if let c = Ctr::None {
                        return false;
                    }

                    let ret = arg_types[idx] == c.to_type();
                    if ret {
                        idx += 1;
                    }
                    return ret;
                });

                if passes && idx < (arg_types.len() - 1) {
                    Err(format!(
                        "{} too little arguments in call to {}",
                        arg_types.len() - (idx + 1),
                        self.name
                    ));
                }

                if !passes {
                    if idx < (arg_types.len() - 1) {
                        Err(format!(
                            "argument {} in call to {} is of wrong type (expected {})",
                            idx + 1,
                            self.name,
                            arg_types[idx].to_str()
                        ));
                    }

                    if idx == (arg_types.len() - 1) {
                        Err(format!(
                            "too many arguments in call to {}",
                            self.name
                        ));
                    }
                }
            }
        }

        self.times_called += 1;
        return Ok((self.function)(args, vars, funcs));
    }
}

impl FTable {
    pub fn declare(
        &mut self,
        f: Function
    ) {
        // memory leak here? where does Function go? maybe it should be boxed....
        self.insert(f.name, f);
    }

    pub fn get(
        &mut self,
        identifier: String
    ) -> Result<Box<Cell>, String> {
        self.get(identifier)
    }
}