Add Brainfuck functio interpretation

BF functios can now be declared and called from AbleScript code.
Function parameters supplied from AbleScript are serialized manually
into byte sequences using the `BfWriter` trait, and are available from
BF code using the input operator, `,`.

At the moment, BF functios simply write output to stdout, and are
therefore incapable of communicating results to the rest of the
program; this might change in the future if we can get something close
to pass-by-reference working.

src/error.rs

@@ -1,5 +1,7 @@
 use std::ops::Range;
 
+use crate::brian::InterpretError;
+
 #[derive(Debug, Clone)]
 pub struct Error {
     pub kind: ErrorKind,
@@ -16,4 +18,5 @@ pub enum ErrorKind {
     TypeError(String),
     TopLevelBreak,
     ArithmeticError,
+    BfInterpretError(InterpretError),
 }

src/interpret.rs

@@ -8,13 +8,16 @@
 
 #[deny(missing_docs)]
 use std::collections::HashMap;
-use std::convert::TryFrom;
+use std::{
+    convert::TryFrom,
+    io::{stdout, Write},
+};
 
 use crate::{
     base_55,
     error::{Error, ErrorKind},
     parser::item::{Expr, Iden, Item, Stmt},
-    variables::{Value, Variable},
+    variables::{Functio, Value, Variable},
 };
 
 /// An environment for executing AbleScript code.
@@ -178,29 +181,64 @@ impl ExecEnv {
                     None => Value::Nul,
                 };
 
-                // There's always at least one stack frame on the
+                self.decl_var(&iden.0, init);
-                // stack if we're evaluating something, so we can
-                // `unwrap` here.
-                self.stack.iter_mut().last().unwrap().variables.insert(
-                    iden.0.clone(),
-                    Variable {
-                        melo: false,
-                        value: init,
-                    },
-                );
             }
             Stmt::FunctionDeclaration {
                 iden: _,
                 args: _,
                 body: _,
             } => todo!(),
-            Stmt::BfFDeclaration { iden: _, body: _ } => todo!(),
+            Stmt::BfFDeclaration { iden, body } => {
+                self.decl_var(
+                    &iden.0,
+                    Value::Functio(Functio::BfFunctio(body.as_bytes().into())),
+                );
+            }
             Stmt::If { cond, body } => {
                 if self.eval_expr(cond)?.into() {
                     return self.eval_items_hs(body);
                 }
             }
-            Stmt::FunctionCall { iden: _, args: _ } => todo!(),
+            Stmt::FunctionCall { iden, args } => {
+                let func = self.get_var(&iden.0)?;
+                match func {
+                    Value::Functio(func) => {
+                        match func {
+                            Functio::BfFunctio(body) => {
+                                use crate::variables::BfWriter;
+                                let mut input: Vec<u8> = vec![];
+                                for arg in args {
+                                    input.write_value(&self.eval_expr(arg)?);
+                                }
+                                println!("input = {:?}", input);
+                                let mut output = vec![];
+
+                                crate::brian::interpret_with_io(&body, &input as &[_], &mut output)
+                                    .map_err(|e| Error {
+                                        kind: ErrorKind::BfInterpretError(e),
+                                        position: 0..0,
+                                    })?;
+
+                                // I guess Brainfuck functions write
+                                // output to stdout? It's not quite
+                                // clear to me what else to do. ~~Alex
+                                stdout()
+                                    .write_all(&output)
+                                    .expect("Failed to write to stdout");
+                            }
+                            Functio::AbleFunctio(_) => {
+                                todo!()
+                            }
+                        }
+                    }
+                    _ => {
+                        return Err(Error {
+                            kind: ErrorKind::TypeError(iden.0.to_owned()),
+                            position: 0..0,
+                        })
+                    }
+                }
+            }
             Stmt::Loop { body } => loop {
                 let res = self.eval_items_hs(body)?;
                 match res {
@@ -289,6 +327,16 @@ impl ExecEnv {
             }),
         }
     }
+
+    /// Declares a new variable, with the given initial value.
+    fn decl_var(&mut self, name: &str, value: Value) {
+        self.stack
+            .iter_mut()
+            .last()
+            .expect("Declaring variable on empty stack")
+            .variables
+            .insert(name.to_owned(), Variable { melo: false, value });
+    }
 }
 
 #[cfg(test)]

src/variables.rs

@@ -1,8 +1,11 @@
-use std::{convert::TryFrom, fmt::Display};
+use std::{convert::TryFrom, fmt::Display, io::Write};
 
 use rand::Rng;
 
-use crate::error::{Error, ErrorKind};
+use crate::{
+    error::{Error, ErrorKind},
+    parser::item::Item,
+};
 
 #[derive(Debug, Clone, PartialEq)]
 pub enum Abool {
@@ -31,23 +34,45 @@ impl From<Abool> for bool {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum Functio {
+    BfFunctio(Vec<u8>),
+    AbleFunctio(Vec<Item>),
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub enum Value {
+    Nul,
     Str(String),
     Int(i32),
     Bool(bool),
     Abool(Abool),
-    Nul,
+    Functio(Functio),
 }
 
 impl Display for Value {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
+            Value::Nul => write!(f, "nul"),
             Value::Str(v) => write!(f, "{}", v),
             Value::Int(v) => write!(f, "{}", v),
             Value::Bool(v) => write!(f, "{}", v),
             Value::Abool(v) => write!(f, "{}", v),
-            Value::Nul => write!(f, "nul"),
+            Value::Functio(v) => match v {
+                Functio::BfFunctio(source) => {
+                    write!(
+                        f,
+                        "{}",
+                        String::from_utf8(source.to_owned())
+                            .expect("Brainfuck functio source should be UTF-8")
+                    )
+                }
+                Functio::AbleFunctio(source) => {
+                    // TODO: what's the proper way to display an
+                    // AbleScript functio?
+                    write!(f, "{:?}", source)
+                }
+            },
         }
     }
 }
@@ -84,6 +109,8 @@ impl From<Value> for bool {
             Value::Str(s) => s.len() != 0,
             // 0 is falsey, nonzero is truthy.
             Value::Int(x) => x != 0,
+            // Functios are always truthy.
+            Value::Functio(_) => true,
             // And nul is truthy as a symbol of the fact that the
             // deep, fundamental truth of this world is nothing but
             // the eternal void.
@@ -92,6 +119,70 @@ impl From<Value> for bool {
     }
 }
 
+/// Allows writing AbleScript values to Brainfuck.
+///
+/// This trait is blanket implemented for all `Write`rs, but should
+/// typically only be used for `Write`rs that cannot fail, e.g.,
+/// `Vec<u8>`, because any IO errors will cause a panic.
+///
+/// The mapping from values to encodings is as follows, where all
+/// multi-byte integers are little-endian:
+///
+/// | AbleScript representation | Brainfuck representation                                  |
+/// |---------------------------|-----------------------------------------------------------|
+/// | Nul                       | 00                                                        |
+/// | Str                       | 01 [length, 4 bytes] [string, \[LENGTH\] bytes, as UTF-8] |
+/// | Int                       | 02 [value, 4 bytes]                                       |
+/// | Bool                      | 03 00 false, 03 01 true.                                  |
+/// | Abool                     | 04 00 never, 04 01 always, 04 02 sometimes.               |
+/// | Brainfuck Functio         | 05 00 [length, 4 bytes] [source code, \[LENGTH\] bytes]   |
+/// | AbleScript Functio        | 05 01 (todo, not yet finalized or implemented)            |
+///
+/// The existing mappings should never change, as they are directly
+/// visible from Brainfuck code and modifying them would break a
+/// significant amount of AbleScript code. If more types are added in
+/// the future, they should be assigned the remaining discriminant
+/// bytes from 06..FF.
+pub trait BfWriter {
+    /// Write a value. Panic if writing fails for any reason.
+    fn write_value(&mut self, value: &Value);
+}
+
+impl<T: Write> BfWriter for T {
+    fn write_value(&mut self, value: &Value) {
+        match value {
+            Value::Nul => self.write_all(&[0]),
+            Value::Str(s) => self
+                .write_all(&[1])
+                .and_then(|_| self.write_all(&(s.len() as u32).to_le_bytes()))
+                .and_then(|_| self.write_all(&s.as_bytes())),
+            Value::Int(v) => self
+                .write_all(&[2])
+                .and_then(|_| self.write_all(&v.to_le_bytes())),
+            Value::Bool(b) => self
+                .write_all(&[3])
+                .and_then(|_| self.write_all(&[*b as _])),
+            Value::Abool(a) => self.write_all(&[4]).and_then(|_| {
+                self.write_all(&[match *a {
+                    Abool::Never => 0,
+                    Abool::Sometimes => 2,
+                    Abool::Always => 1,
+                }])
+            }),
+            Value::Functio(f) => self.write_all(&[5]).and_then(|_| match f {
+                Functio::BfFunctio(f) => self
+                    .write_all(&[0])
+                    .and_then(|_| self.write_all(&(f.len() as u32).to_le_bytes()))
+                    .and_then(|_| self.write_all(&f)),
+                Functio::AbleFunctio(_) => {
+                    todo!()
+                }
+            }),
+        }
+        .expect("Failed to write to Brainfuck input");
+    }
+}
+
 #[derive(Debug)]
 pub struct Variable {
     pub melo: bool,