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Better abstractions, implement scoping rules

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This commit is contained in:
Alexander Bethel 2021-05-25 13:26:01 -05:00
parent 1c2032ab87
commit e7560f9364
3 changed files with 109 additions and 69 deletions
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166
src/interpret.rs
View file

@ -1,10 +1,10 @@
//! Expression evaluator and statement interpreter.
//!
//! To interpret a piece of AbleScript code, you first need to
//! construct a [Scope], which is responsible for storing the list of
//! variable and function definitions accessible from an AbleScript
//! snippet. You can then call [Scope::eval_items] to evaluate or
//! execute any number of expressions or statements.
//! construct an [ExecEnv], which is responsible for storing the stack
//! of local variable and function definitions accessible from an
//! AbleScript snippet. You can then call [ExecEnv::eval_items] to
//! evaluate or execute any number of expressions or statements.
#[deny(missing_docs)]
use std::collections::HashMap;
@ -16,33 +16,49 @@ use crate::{
variables::{Value, Variable},
};
/// A set of visible variable and function definitions, which serves
/// as a context in which expressions can be evaluated.
pub struct Scope {
/// The mapping from variable names to values.
variables: HashMap<String, Variable>,
// In the future, this will store functio definitions, a link to a
// parent scope (so we can have nested scopes), and possibly other
// information.
/// An environment for executing AbleScript code.
pub struct ExecEnv {
/// The stack, ordered such that `stack[stack.len() - 1]` is the
/// top-most (newest) stack frame, and `stack[0]` is the
/// bottom-most (oldest) stack frame.
stack: Vec<Scope>,
}
impl Scope {
/// A set of visible variable and function definitions, which serves
/// as a context in which expressions can be evaluated.
#[derive(Default)]
struct Scope {
/// The mapping from variable names to values.
variables: HashMap<String, Variable>,
// In the future, this will store functio definitions and possibly
// other information.
}
impl ExecEnv {
/// Create a new Scope with no predefined variable definitions or
/// other information.
pub fn new() -> Self {
Self {
variables: HashMap::new(),
stack: Default::default(),
}
}
/// Evaluate a set of Items. Returns the value of the last Item
/// evaluated, or an error if one or more of the Items failed to
/// evaluate.
/// Evaluate a set of Items in their own stack frame. Return the
/// value of the last Item evaluated, or an error if one or more
/// of the Items failed to evaluate.
pub fn eval_items(&mut self, items: &[Item]) -> Result<Value, Error> {
items
let init_depth = self.stack.len();
self.stack.push(Default::default());
let res = items
.iter()
.map(|item| self.eval_item(item))
.try_fold(Value::Nul, |_, result| result)
.try_fold(Value::Nul, |_, result| result);
self.stack.pop();
// Invariant: stack size must have net 0 change.
debug_assert_eq!(self.stack.len(), init_depth);
res
}
/// Evaluate a single Item, returning its value or an error.
@ -89,25 +105,7 @@ impl Scope {
}
Not(expr) => Bool(!bool::from(self.eval_expr(expr)?)),
Literal(value) => value.clone(),
Identifier(Iden(name)) => self
.variables
.get(name)
.ok_or_else(|| Error {
kind: ErrorKind::UnknownVariable(name.to_owned()),
// TODO: figure out some way to avoid this 0..0
// dumbness
position: 0..0,
})
.and_then(|var| {
if !var.melo {
Ok(var.value.clone())
} else {
Err(Error {
kind: ErrorKind::MeloVariable(name.to_owned()),
position: 0..0,
})
}
})?,
Identifier(Iden(name)) => self.get_var(name)?.value.clone(),
})
}
@ -118,14 +116,19 @@ impl Scope {
println!("{}", self.eval_expr(expr)?);
}
Stmt::VariableDeclaration { iden, init } => {
self.variables.insert(
let init = match init {
Some(e) => self.eval_expr(e)?,
None => Value::Nul,
};
// There's always at least one stack frame on the
// 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: match init {
Some(init) => self.eval_expr(init)?,
None => Value::Nul,
},
value: init,
},
);
}
@ -149,33 +152,70 @@ impl Scope {
}
}
Stmt::VarAssignment { iden, value } => {
let value = self.eval_expr(value)?;
let record = self.variables.get_mut(&iden.0).ok_or_else(|| Error {
kind: ErrorKind::UnknownVariable(iden.0.clone()),
position: 0..0,
})?;
if record.melo {
return Err(Error {
kind: ErrorKind::MeloVariable(iden.0.clone()),
position: 0..0,
});
}
record.value = value;
self.get_var_mut(&iden.0)?.value = self.eval_expr(value)?;
}
Stmt::Break => todo!(),
Stmt::HopBack => todo!(),
Stmt::Melo(iden) => {
let record = self.variables.get_mut(&iden.0).ok_or_else(|| Error {
kind: ErrorKind::UnknownVariable(iden.0.clone()),
position: 0..0,
})?;
record.melo = true;
self.get_var_mut(&iden.0)?.melo = true;
}
}
Ok(())
}
/// Get a shared reference to the value of a variable. Throw an
/// error if the variable is inaccessible or banned.
fn get_var(&self, name: &str) -> Result<&Variable, Error> {
match self
.stack
.iter()
.rev()
.find_map(|scope| scope.variables.get(name))
{
Some(var) => {
if !var.melo {
Ok(var)
} else {
Err(Error {
kind: ErrorKind::MeloVariable(name.to_owned()),
// TODO: figure out some way to avoid this
// 0..0 dumbness
position: 0..0,
})
}
}
None => Err(Error {
kind: ErrorKind::UnknownVariable(name.to_owned()),
position: 0..0,
}),
}
}
/// Get a mutable reference to a variable. Throw an error if the
/// variable is inaccessible or banned.
fn get_var_mut(&mut self, name: &str) -> Result<&mut Variable, Error> {
// FIXME: This function is almost exactly the same as get_var.
match self
.stack
.iter_mut()
.rev()
.find_map(|scope| scope.variables.get_mut(name))
{
Some(var) => {
if !var.melo {
Ok(var)
} else {
Err(Error {
kind: ErrorKind::MeloVariable(name.to_owned()),
position: 0..0,
})
}
}
None => Err(Error {
kind: ErrorKind::UnknownVariable(name.to_owned()),
position: 0..0,
}),
}
}
}

6
src/main.rs
View file

@ -10,7 +10,7 @@ mod repl;
mod variables;
use clap::{App, Arg};
use interpret::Scope;
use interpret::ExecEnv;
use logos::Source;
use parser::Parser;
@ -41,8 +41,8 @@ fn main() {
match ast {
Ok(ast) => {
println!("{:#?}", ast);
let mut ctx = Scope::new();
println!("{:?}", ctx.eval_items(&ast));
let mut env = ExecEnv::new();
println!("{:?}", env.eval_items(&ast));
}
Err(e) => {
println!(

6
src/repl.rs
View file

@ -1,11 +1,11 @@
use logos::Source;
use rustyline::Editor;
use crate::{interpret::Scope, parser::Parser};
use crate::{interpret::ExecEnv, parser::Parser};
pub fn repl() {
let mut rl = Editor::<()>::new();
let mut ctx = Scope::new();
let mut env = ExecEnv::new();
loop {
let readline = rl.readline(":: ");
match readline {
@ -19,7 +19,7 @@ pub fn repl() {
match ast {
Ok(ast) => {
println!("{:?}", ast);
println!("{:?}", ctx.eval_items(&ast));
println!("{:?}", env.eval_items(&ast));
},
Err(e) => {
println!(