src/eval.rs

@@ -0,0 +1,15 @@
+mod env;
+mod primop;
+mod value;
+
+pub use env::{EvalEnvironment, LookupError};
+pub use primop::PrimOpError;
+pub use value::Value;
+
+#[derive(Clone, Debug, PartialEq, thiserror::Error)]
+pub enum EvalError {
+    #[error(transparent)]
+    Lookup(#[from] LookupError),
+    #[error(transparent)]
+    PrimOp(#[from] PrimOpError),
+}

src/eval/env.rs

@@ -0,0 +1,92 @@
+use crate::eval::Value;
+use internment::ArcIntern;
+use std::sync::Arc;
+
+pub struct EvalEnvironment {
+    inner: Arc<EvalEnvInternal>,
+}
+
+pub enum EvalEnvInternal {
+    Empty,
+    Value(ArcIntern<String>, Value, Arc<EvalEnvInternal>),
+}
+
+
+#[derive(Clone, Debug, PartialEq, thiserror::Error)]
+pub enum LookupError {
+    #[error("Could not find variable '{0}' in environment")]
+    CouldNotFind(ArcIntern<String>),
+}
+
+impl Default for EvalEnvironment {
+    fn default() -> Self {
+        EvalEnvironment::empty()
+    }
+}
+
+impl EvalEnvironment {
+    pub fn empty() -> Self {
+        EvalEnvironment { inner: Arc::new(EvalEnvInternal::Empty) }
+    }
+
+    pub fn extend(&self, name: ArcIntern<String>, value: Value) -> Self {
+        EvalEnvironment {
+            inner: Arc::new(EvalEnvInternal::Value(name, value, self.inner.clone()))
+        }
+    }
+
+    pub fn lookup(&self, n: ArcIntern<String>) -> Result<Value, LookupError> {
+        self.inner.lookup(n)
+    }
+}
+
+impl EvalEnvInternal {
+    fn lookup(&self, n: ArcIntern<String>) -> Result<Value, LookupError> {
+        match self {
+            EvalEnvInternal::Empty => Err(LookupError::CouldNotFind(n)),
+            EvalEnvInternal::Value(name, value, _) if *name == n => Ok(value.clone()),
+            EvalEnvInternal::Value(_, _, rest) => rest.lookup(n),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use internment::ArcIntern;
+
+    use super::EvalEnvironment;
+
+    #[test]
+    fn simple_lookups() {
+        let tester = EvalEnvironment::default();
+        let tester = tester.extend(arced("foo"), 1i64.into());
+        let tester = tester.extend(arced("bar"), 2i64.into());
+        let tester = tester.extend(arced("goo"), 5i64.into());
+
+        assert_eq!(tester.lookup(arced("foo")), Ok(1.into()));
+        assert_eq!(tester.lookup(arced("bar")), Ok(2.into()));
+        assert_eq!(tester.lookup(arced("goo")), Ok(5.into()));
+        assert!(tester.lookup(arced("baz")).is_err());
+    }
+
+    #[test]
+    fn nested() {
+        let tester = EvalEnvironment::default();
+        let tester = tester.extend(arced("foo"), 1i64.into());
+
+        check_nested(&tester);
+
+        assert_eq!(tester.lookup(arced("foo")), Ok(1.into()));
+        assert!(tester.lookup(arced("bar")).is_err());
+    }
+
+    fn check_nested(env: &EvalEnvironment) {
+        let nested_env = env.extend(arced("bar"), 2i64.into());
+        assert_eq!(nested_env.lookup(arced("foo")), Ok(1.into()));
+        assert_eq!(nested_env.lookup(arced("bar")), Ok(2.into()));
+    }
+
+    fn arced(s: &str) -> ArcIntern<String> {
+        ArcIntern::new(s.to_string())
+    }
+}

src/eval/primop.rs

@@ -0,0 +1,46 @@
+use crate::eval::value::Value;
+
+#[derive(Clone, Debug, PartialEq, thiserror::Error)]
+pub enum PrimOpError {
+    #[error("Math error (underflow or overflow) computing {0} operator")]
+    MathFailure(&'static str),
+    #[error("Type mismatch ({1} vs {2}) computing {0} operator")]
+    TypeMismatch(String, Value, Value),
+    #[error("Bad type for operator {0}: {1}")]
+    BadTypeFor(&'static str, Value),
+    #[error("Illegal number of arguments for {0}: {1} arguments found")]
+    BadArgCount(String, usize),
+    #[error("Unknown primitive operation {0}")]
+    UnknownPrimOp(String),
+}
+
+macro_rules! run_op {
+    ($op: ident, $left: expr, $right: expr) => {
+        match $op {
+            "+" => $left.checked_add($right).ok_or(PrimOpError::MathFailure("+")).map(Into::into),
+            "-" => $left.checked_sub($right).ok_or(PrimOpError::MathFailure("+")).map(Into::into),
+            "*" => $left.checked_mul($right).ok_or(PrimOpError::MathFailure("+")).map(Into::into),
+            "/" => $left.checked_div($right).ok_or(PrimOpError::MathFailure("+")).map(Into::into),
+            _ => Err(PrimOpError::UnknownPrimOp($op.to_string())),
+        } 
+    };
+}
+
+impl Value {
+    fn binary_op(operation: &str, left: &Value, right: &Value) -> Result<Value, PrimOpError> {
+        match left {
+            Value::I64(x) => match right {
+                Value::I64(y) => run_op!(operation, x, *y),
+                _ => Err(PrimOpError::TypeMismatch(operation.to_string(), left.clone(), right.clone()))
+            }
+        }
+    }
+
+    pub fn calculate(operation: &str, values: Vec<Value>) -> Result<Value, PrimOpError> {
+        if values.len() == 2 {
+            Value::binary_op(operation, &values[0], &values[1])
+        } else {
+            Err(PrimOpError::BadArgCount(operation.to_string(), values.len()))
+        }
+    }
+}

src/eval/value.rs

@@ -0,0 +1,20 @@
+use std::fmt::Display;
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Value {
+    I64(i64),
+}
+
+impl Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Value::I64(x) => write!(f, "{}i64", x),
+        }
+    }
+}
+
+impl From<i64> for Value {
+    fn from(value: i64) -> Self {
+        Value::I64(value)
+    }
+}

src/ir.rs

@@ -1,4 +1,5 @@
 mod ast;
+mod eval;
 mod from_syntax;
 mod strings;
 

src/ir/eval.rs

@@ -0,0 +1,76 @@
+use internment::ArcIntern;
+
+use crate::eval::{EvalEnvironment, EvalError, Value};
+use crate::ir::{Program, Statement, Expression};
+
+use super::{ValueOrRef, Primitive};
+
+impl Program {
+    pub fn eval(&self) -> Result<String, EvalError> {
+        let mut env = EvalEnvironment::empty();
+        let mut stdout = String::new();
+
+        for stmt in self.statements.iter() {
+            match stmt {
+                Statement::Binding(_, name, value) => {
+                    let actual_value = value.eval(&env)?;
+                    env = env.extend(name.clone(), actual_value);
+                }
+
+                Statement::Print(_, name) => {
+                    let value = env.lookup(name.clone())?;
+                    let line = format!("{} = {}\n", name, value);
+                    stdout.push_str(&line);
+                }
+            }
+        }
+
+        Ok(stdout)
+    }
+}
+
+impl Expression {
+    fn eval(&self, env: &EvalEnvironment) -> Result<Value, EvalError> {
+        match self {
+            Expression::Value(_, v) => match v {
+                super::Value::Number(_, v) => Ok(Value::I64(*v)),
+            }
+
+            Expression::Reference(_, n) => Ok(env.lookup(n.clone())?),
+
+            Expression::Primitive(_, op, args) => {
+                let mut arg_values = Vec::with_capacity(args.len());
+
+                for arg in args.iter() {
+                    match arg {
+                        ValueOrRef::Ref(_, n) => arg_values.push(env.lookup(n.clone())?),
+                        ValueOrRef::Value(_, super::Value::Number(_, v)) => arg_values.push(Value::I64(*v)),
+                    }
+                }
+
+                match op {
+                    Primitive::Plus => Ok(Value::calculate("+", arg_values)?),
+                    Primitive::Minus => Ok(Value::calculate("-", arg_values)?),
+                    Primitive::Times => Ok(Value::calculate("*", arg_values)?),
+                    Primitive::Divide => Ok(Value::calculate("/", arg_values)?),
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn two_plus_three() {
+    let input = crate::syntax::Program::parse(0, "x = 2 + 3; print x;").expect("parse works");
+    let ir = Program::from(input.simplify());
+    let output = ir.eval().expect("runs successfully");
+    assert_eq!("x = 5i64\n", &output);
+}
+
+#[test]
+fn lotsa_math() {
+    let input = crate::syntax::Program::parse(0, "x = 2 + 3 * 10 / 5 - 1; print x;").expect("parse works");
+    let ir = Program::from(input.simplify());
+    let output = ir.eval().expect("runs successfully");
+    assert_eq!("x = 7i64\n", &output);
+}

src/ir/from_syntax.rs

@@ -71,3 +71,13 @@ impl From<syntax::Value> for ir::Value {
         }
     }
 }
+
+proptest::proptest! {
+    #[test]
+    fn translation_maintains_semantics(input: syntax::Program) {
+        let syntax_result = input.eval();
+        let ir = ir::Program::from(input.simplify());
+        let ir_result = ir.eval();
+        assert_eq!(syntax_result, ir_result);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
 pub mod backend;
+pub mod eval;
 pub mod ir;
 pub mod syntax;

src/syntax.rs

@@ -4,6 +4,7 @@ use logos::Logos;
 
 mod arbitrary;
 pub mod ast;
+mod eval;
 mod location;
 mod simplify;
 mod tokens;
@@ -17,7 +18,7 @@ mod validate;
 
 pub use crate::syntax::ast::*;
 pub use crate::syntax::location::Location;
-use crate::syntax::parser::ProgramParser;
+use crate::{syntax::parser::ProgramParser, eval::EvalError};
 pub use crate::syntax::tokens::{LexerError, Token};
 #[cfg(test)]
 use ::pretty::{Arena, Pretty};
@@ -269,4 +270,10 @@ proptest::proptest! {
         let (errors, _) = program.validate();
         prop_assert!(errors.is_empty());
      }
+
+     #[test]
+     fn generated_run_or_overflow(program: Program) {
+        use crate::eval::PrimOpError;
+        assert!(matches!(program.eval(), Ok(_) | Err(EvalError::PrimOp(PrimOpError::MathFailure(_)))))
+     }
 }

src/syntax/eval.rs

@@ -0,0 +1,64 @@
+use internment::ArcIntern;
+
+use crate::eval::{EvalEnvironment, EvalError, Value};
+use crate::syntax::{Program, Statement, Expression};
+
+impl Program {
+    pub fn eval(&self) -> Result<String, EvalError> {
+        let mut env = EvalEnvironment::empty();
+        let mut stdout = String::new();
+
+        for stmt in self.statements.iter() {
+            match stmt {
+                Statement::Binding(_, name, value) => {
+                    let actual_value = value.eval(&env)?;
+                    env = env.extend(ArcIntern::new(name.clone()), actual_value);
+                }
+
+                Statement::Print(_, name) => {
+                    let value = env.lookup(ArcIntern::new(name.clone()))?;
+                    let line = format!("{} = {}\n", name, value);
+                    stdout.push_str(&line);
+                }
+            }
+        }
+
+        Ok(stdout)
+    }
+}
+
+impl Expression {
+    fn eval(&self, env: &EvalEnvironment) -> Result<Value, EvalError> {
+        match self {
+            Expression::Value(_, v) => match v {
+                super::Value::Number(_, v) => Ok(Value::I64(*v)),
+            }
+
+            Expression::Reference(_, n) => Ok(env.lookup(ArcIntern::new(n.clone()))?),
+
+            Expression::Primitive(_, op, args) => {
+                let mut arg_values = Vec::with_capacity(args.len());
+
+                for arg in args.iter() {
+                    arg_values.push(arg.eval(env)?);
+                }
+
+                Ok(Value::calculate(op, arg_values)?)
+            }
+        }
+    }
+}
+
+#[test]
+fn two_plus_three() {
+    let input = Program::parse(0, "x = 2 + 3; print x;").expect("parse works");
+    let output = input.eval().expect("runs successfully");
+    assert_eq!("x = 5i64\n", &output);
+}
+
+#[test]
+fn lotsa_math() {
+    let input = Program::parse(0, "x = 2 + 3 * 10 / 5 - 1; print x;").expect("parse works");
+    let output = input.eval().expect("runs successfully");
+    assert_eq!("x = 7i64\n", &output);
+}