/home/noah/src/ruchy/src/transpiler/reference_interpreter.rs

Source
//! Reference Interpreter - Ground Truth for Semantic Verification
//!
//! A minimal, unoptimized, obviously correct interpreter for the core language.
//! This serves as the oracle for differential testing against the transpiler.
//!
//! Design principles:
//! - Clarity over performance
//! - No optimizations whatsoever
//! - Under 1000 LOC
//! - Direct operational semantics

#![allow(clippy::cast_possible_truncation)] // Reference interpreter prioritizes simplicity
#![allow(clippy::cast_sign_loss)] // Reference interpreter uses simple casts
#![allow(clippy::cast_possible_wrap)] // Reference interpreter uses simple casts

use crate::transpiler::canonical_ast::{CoreExpr, CoreLiteral, DeBruijnIndex, PrimOp};
use std::rc::Rc;

/// Runtime values
#[derive(Debug, Clone, PartialEq)]
pub enum Value {
    Integer(i64),
    Float(f64),
    String(String),
    Bool(bool),
    Char(char),
    Unit,
    Nil,
    /// Closure captures the body and environment at creation time
    Closure {
        body: Rc<CoreExpr>,
        env: Environment,
    },
    /// Arrays are just vectors
    Array(Vec<Value>),
}

/// Environment for variable bindings
#[derive(Debug, Clone, PartialEq)]
pub struct Environment {
    bindings: Vec<Value>,
}

impl Default for Environment {
    fn default() -> Self {
        Self::new()
    }
}

impl Environment {
    #[must_use]
    pub fn new() -> Self {
        Self {
            bindings: Vec::new(),
        }
    }

    pub fn push(&mut self, value: Value) {
        self.bindings.push(value);
    }

    pub fn pop(&mut self) {
        self.bindings.pop();
    }

    #[must_use]
    pub fn lookup(&self, index: &DeBruijnIndex) -> Option<&Value> {
        // De Bruijn indices count from the end
        let pos = self.bindings.len().checked_sub(index.0 + 1)?;
        self.bindings.get(pos)
    }
}

/// Reference interpreter - deliberately simple and unoptimized
pub struct ReferenceInterpreter {
    env: Environment,
    trace: Vec<String>, // For debugging
}

impl Default for ReferenceInterpreter {
    fn default() -> Self {
        Self::new()
    }
}

impl ReferenceInterpreter {
    #[must_use]
    pub fn new() -> Self {
        Self {
            env: Environment::new(),
            trace: Vec::new(),
        }
    }

    /// Evaluate an expression to a value
    /// This is the core of the interpreter - direct operational semantics
    /// # Errors
    ///
    /// Returns an error if the operation fails
    /// # Errors
    ///
    /// Returns an error if the operation fails
    pub fn eval(&mut self, expr: &CoreExpr) -> Result<Value, String> {
        self.trace.push(format!("Evaluating: {expr:?}"));

        match expr {
            CoreExpr::Var(idx) => self
                .env
                .lookup(idx)
                .cloned()
                .ok_or_else(|| format!("Unbound variable: {idx:?}")),

            CoreExpr::Lambda { body, .. } => {
                // Create closure capturing current environment
                Ok(Value::Closure {
                    body: Rc::new(body.as_ref().clone()),
                    env: self.env.clone(),
                })
            }

            CoreExpr::App(func, arg) => {
                // Evaluate function
                let func_val = self.eval(func)?;

                // Evaluate argument (call-by-value)
                let arg_val = self.eval(arg)?;

                // Apply function to argument
                match func_val {
                    Value::Closure { body, mut env } => {
                        // Save current environment
                        let saved_env = self.env.clone();

                        // Set up closure environment with argument
                        env.push(arg_val);
                        self.env = env;

                        // Evaluate body
                        let result = self.eval(&body)?;

                        // Restore environment
                        self.env = saved_env;

                        Ok(result)
                    }
                    _ => Err(format!("Cannot apply non-function: {func_val:?}")),
                }
            }

            CoreExpr::Let { value, body, name } => {
                self.trace.push(format!("Let binding: {name:?}"));

                // Evaluate the value
                let val = self.eval(value)?;

                // Bind it in the environment
                self.env.push(val);

                // Evaluate the body
                let result = self.eval(body)?;

                // Pop the binding
                self.env.pop();

                Ok(result)
            }

            CoreExpr::Literal(lit) => Ok(match lit {
                CoreLiteral::Integer(i) => Value::Integer(*i),
                CoreLiteral::Float(f) => Value::Float(*f),
                CoreLiteral::String(s) => Value::String(s.clone()),
                CoreLiteral::Bool(b) => Value::Bool(*b),
                CoreLiteral::Char(c) => Value::Char(*c),
                CoreLiteral::Unit => Value::Unit,
            }),

            CoreExpr::Prim(op, args) => self.eval_prim(op, args),
        }
    }

    /// Evaluate primitive operations
    #[allow(clippy::too_many_lines)] // Comprehensive primitive operations
    fn eval_prim(&mut self, op: &PrimOp, args: &[CoreExpr]) -> Result<Value, String> {
        // Evaluate all arguments first (strict evaluation)
        let mut values = Vec::new();
        for arg in args {
            values.push(self.eval(arg)?);
        }

        match op {
            // Arithmetic operations
            PrimOp::Add => {
                if values.len() != 2 {
                    return Err(format!("Add expects 2 arguments, got {}", values.len()));
                }
                match (&values[0], &values[1]) {
                    (Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a + b)),
                    (Value::Float(a), Value::Float(b)) => Ok(Value::Float(a + b)),
                    (Value::String(a), Value::String(b)) => Ok(Value::String(format!("{a}{b}"))),
                    _ => Err(format!(
                        "Type error in addition: {:?} + {:?}",
                        values[0], values[1]
                    )),
                }
            }

            PrimOp::Sub => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a - b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Float(a - b)),
                _ => Err("Type error in subtraction".to_string()),
            },

            PrimOp::Mul => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a * b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Float(a * b)),
                _ => Err("Type error in multiplication".to_string()),
            },

            PrimOp::Div => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => {
                    if *b == 0 {
                        Err("Division by zero".to_string())
                    } else {
                        Ok(Value::Integer(a / b))
                    }
                }
                (Value::Float(a), Value::Float(b)) => {
                    if *b == 0.0 {
                        Err("Division by zero".to_string())
                    } else {
                        Ok(Value::Float(a / b))
                    }
                }
                _ => Err("Type error in division".to_string()),
            },

            PrimOp::Mod => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => {
                    if *b == 0 {
                        Err("Modulo by zero".to_string())
                    } else {
                        Ok(Value::Integer(a % b))
                    }
                }
                _ => Err("Type error in modulo".to_string()),
            },

            PrimOp::Pow => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => {
                    if *b < 0 {
                        Err("Negative exponent for integer".to_string())
                    } else {
                        Ok(Value::Integer(a.pow(*b as u32)))
                    }
                }
                (Value::Float(a), Value::Float(b)) => Ok(Value::Float(a.powf(*b))),
                _ => Err("Type error in power".to_string()),
            },

            // Comparison operations
            PrimOp::Eq => Ok(Value::Bool(values[0] == values[1])),

            PrimOp::Ne => Ok(Value::Bool(values[0] != values[1])),

            PrimOp::Lt => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a < b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a < b)),
                _ => Err("Type error in less-than".to_string()),
            },

            PrimOp::Le => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a <= b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a <= b)),
                _ => Err("Type error in less-equal".to_string()),
            },

            PrimOp::Gt => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a > b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a > b)),
                _ => Err("Type error in greater-than".to_string()),
            },

            PrimOp::Ge => match (&values[0], &values[1]) {
                (Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a >= b)),
                (Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a >= b)),
                _ => Err("Type error in greater-equal".to_string()),
            },

            // Logical operations
            PrimOp::And => match (&values[0], &values[1]) {
                (Value::Bool(a), Value::Bool(b)) => Ok(Value::Bool(*a && *b)),
                _ => Err("Type error in AND".to_string()),
            },

            PrimOp::Or => match (&values[0], &values[1]) {
                (Value::Bool(a), Value::Bool(b)) => Ok(Value::Bool(*a || *b)),
                _ => Err("Type error in OR".to_string()),
            },

            PrimOp::NullCoalesce => {
                if values.len() != 2 {
                    return Err(format!("NullCoalesce expects 2 arguments, got {}", values.len()));
                }
                // Return left if not nil, otherwise right
                match &values[0] {
                    Value::Nil => Ok(values[1].clone()),
                    _ => Ok(values[0].clone()),
                }
            },

            PrimOp::Not => {
                if values.len() != 1 {
                    return Err(format!("NOT expects 1 argument, got {}", values.len()));
                }
                match &values[0] {
                    Value::Bool(b) => Ok(Value::Bool(!b)),
                    _ => Err("Type error in NOT".to_string()),
                }
            }

            // Control flow
            PrimOp::If => {
                if values.len() != 3 {
                    return Err(format!("IF expects 3 arguments, got {}", values.len()));
                }

                // Note: We already evaluated all branches (strict evaluation)
                // A lazy interpreter would evaluate condition first, then the appropriate branch
                match &values[0] {
                    Value::Bool(true) => Ok(values[1].clone()),
                    Value::Bool(false) => Ok(values[2].clone()),
                    _ => Err("Type error: IF condition must be boolean".to_string()),
                }
            }

            // Array operations
            PrimOp::ArrayNew => {
                // Create array from all arguments
                Ok(Value::Array(values))
            }

            PrimOp::ArrayIndex => {
                if values.len() != 2 {
                    return Err("Array index expects 2 arguments".to_string());
                }
                match (&values[0], &values[1]) {
                    (Value::Array(arr), Value::Integer(idx)) => {
                        if *idx < 0 || *idx as usize >= arr.len() {
                            Err(format!("Array index out of bounds: {idx}"))
                        } else {
                            Ok(arr[*idx as usize].clone())
                        }
                    }
                    _ => Err("Type error in array indexing".to_string()),
                }
            }

            PrimOp::ArrayLen => {
                if values.len() != 1 {
                    return Err("Array length expects 1 argument".to_string());
                }
                match &values[0] {
                    Value::Array(arr) => Ok(Value::Integer(arr.len() as i64)),
                    _ => Err("Type error: expected array".to_string()),
                }
            }

            PrimOp::Concat => Err(format!("Unsupported primitive: {op:?}")),
        }
    }

    /// Get execution trace for debugging
    #[must_use]
    pub fn get_trace(&self) -> &[String] {
        &self.trace
    }

    /// Clear the trace
    pub fn clear_trace(&mut self) {
        self.trace.clear();
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests {
    use super::*;
    use crate::transpiler::canonical_ast::AstNormalizer;
    use crate::Parser;

    #[test]
    fn test_eval_arithmetic() {
        let input = "1 + 2 * 3";
        let mut parser = Parser::new(input);
        let ast = parser.parse().unwrap();

        let mut normalizer = AstNormalizer::new();
        let core = normalizer.normalize(&ast);

        let mut interp = ReferenceInterpreter::new();
        let result = interp.eval(&core).unwrap();

        assert_eq!(result, Value::Integer(7)); // 1 + (2 * 3)
    }

    #[test]
    fn test_eval_let_binding() {
        let input = "let x = 10 in ()";
        let mut parser = Parser::new(input);
        let ast = parser.parse().unwrap();

        let mut normalizer = AstNormalizer::new();
        let core = normalizer.normalize(&ast);

        let mut interp = ReferenceInterpreter::new();
        let result = interp.eval(&core).unwrap();

        // Let with unit body evaluates to unit
        assert_eq!(result, Value::Unit);
    }

    #[test]
    fn test_eval_function() {
        // This would need more setup to test properly
        // as we need to handle function definitions and calls
    }
}

Coverage Report

Created: 2025-09-08 21:26

Line	Count	Source
1		//! Reference Interpreter - Ground Truth for Semantic Verification
2		//!
3		//! A minimal, unoptimized, obviously correct interpreter for the core language.
4		//! This serves as the oracle for differential testing against the transpiler.
5		//!
6		//! Design principles:
7		//! - Clarity over performance
8		//! - No optimizations whatsoever
9		//! - Under 1000 LOC
10		//! - Direct operational semantics
11
12		#![allow(clippy::cast_possible_truncation)] // Reference interpreter prioritizes simplicity
13		#![allow(clippy::cast_sign_loss)] // Reference interpreter uses simple casts
14		#![allow(clippy::cast_possible_wrap)] // Reference interpreter uses simple casts
15
16		use crate::transpiler::canonical_ast::{CoreExpr, CoreLiteral, DeBruijnIndex, PrimOp};
17		use std::rc::Rc;
18
19		/// Runtime values
20		#[derive(Debug, Clone, PartialEq)]
21		pub enum Value {
22		Integer(i64),
23		Float(f64),
24		String(String),
25		Bool(bool),
26		Char(char),
27		Unit,
28		Nil,
29		/// Closure captures the body and environment at creation time
30		Closure {
31		body: Rc<CoreExpr>,
32		env: Environment,
33		},
34		/// Arrays are just vectors
35		Array(Vec<Value>),
36		}
37
38		/// Environment for variable bindings
39		#[derive(Debug, Clone, PartialEq)]
40		pub struct Environment {
41		bindings: Vec<Value>,
42		}
43
44		impl Default for Environment {
45	0	fn default() -> Self {
46	0	Self::new()
47	0	}
48		}
49
50		impl Environment {
51		#[must_use]
52	0	pub fn new() -> Self {
53	0	Self {
54	0	bindings: Vec::new(),
55	0	}
56	0	}
57
58	0	pub fn push(&mut self, value: Value) {
59	0	self.bindings.push(value);
60	0	}
61
62	0	pub fn pop(&mut self) {
63	0	self.bindings.pop();
64	0	}
65
66		#[must_use]
67	0	pub fn lookup(&self, index: &DeBruijnIndex) -> Option<&Value> {
68		// De Bruijn indices count from the end
69	0	let pos = self.bindings.len().checked_sub(index.0 + 1)?;
70	0	self.bindings.get(pos)
71	0	}
72		}
73
74		/// Reference interpreter - deliberately simple and unoptimized
75		pub struct ReferenceInterpreter {
76		env: Environment,
77		trace: Vec<String>, // For debugging
78		}
79
80		impl Default for ReferenceInterpreter {
81	0	fn default() -> Self {
82	0	Self::new()
83	0	}
84		}
85
86		impl ReferenceInterpreter {
87		#[must_use]
88	0	pub fn new() -> Self {
89	0	Self {
90	0	env: Environment::new(),
91	0	trace: Vec::new(),
92	0	}
93	0	}
94
95		/// Evaluate an expression to a value
96		/// This is the core of the interpreter - direct operational semantics
97		/// # Errors
98		///
99		/// Returns an error if the operation fails
100		/// # Errors
101		///
102		/// Returns an error if the operation fails
103	0	pub fn eval(&mut self, expr: &CoreExpr) -> Result<Value, String> {
104	0	self.trace.push(format!("Evaluating: {expr:?}"));
105
106	0	match expr {
107	0	CoreExpr::Var(idx) => self
108	0	.env
109	0	.lookup(idx)
110	0	.cloned()
111	0	.ok_or_else(\|\| format!("Unbound variable: {idx:?}")),
112
113	0	CoreExpr::Lambda { body, .. } => {
114		// Create closure capturing current environment
115	0	Ok(Value::Closure {
116	0	body: Rc::new(body.as_ref().clone()),
117	0	env: self.env.clone(),
118	0	})
119		}
120
121	0	CoreExpr::App(func, arg) => {
122		// Evaluate function
123	0	let func_val = self.eval(func)?;
124
125		// Evaluate argument (call-by-value)
126	0	let arg_val = self.eval(arg)?;
127
128		// Apply function to argument
129	0	match func_val {
130	0	Value::Closure { body, mut env } => {
131		// Save current environment
132	0	let saved_env = self.env.clone();
133
134		// Set up closure environment with argument
135	0	env.push(arg_val);
136	0	self.env = env;
137
138		// Evaluate body
139	0	let result = self.eval(&body)?;
140
141		// Restore environment
142	0	self.env = saved_env;
143
144	0	Ok(result)
145		}
146	0	_ => Err(format!("Cannot apply non-function: {func_val:?}")),
147		}
148		}
149
150	0	CoreExpr::Let { value, body, name } => {
151	0	self.trace.push(format!("Let binding: {name:?}"));
152
153		// Evaluate the value
154	0	let val = self.eval(value)?;
155
156		// Bind it in the environment
157	0	self.env.push(val);
158
159		// Evaluate the body
160	0	let result = self.eval(body)?;
161
162		// Pop the binding
163	0	self.env.pop();
164
165	0	Ok(result)
166		}
167
168	0	CoreExpr::Literal(lit) => Ok(match lit {
169	0	CoreLiteral::Integer(i) => Value::Integer(*i),
170	0	CoreLiteral::Float(f) => Value::Float(*f),
171	0	CoreLiteral::String(s) => Value::String(s.clone()),
172	0	CoreLiteral::Bool(b) => Value::Bool(*b),
173	0	CoreLiteral::Char(c) => Value::Char(*c),
174	0	CoreLiteral::Unit => Value::Unit,
175		}),
176
177	0	CoreExpr::Prim(op, args) => self.eval_prim(op, args),
178		}
179	0	}
180
181		/// Evaluate primitive operations
182		#[allow(clippy::too_many_lines)] // Comprehensive primitive operations
183	0	fn eval_prim(&mut self, op: &PrimOp, args: &[CoreExpr]) -> Result<Value, String> {
184		// Evaluate all arguments first (strict evaluation)
185	0	let mut values = Vec::new();
186	0	for arg in args {
187	0	values.push(self.eval(arg)?);
188		}
189
190	0	match op {
191		// Arithmetic operations
192		PrimOp::Add => {
193	0	if values.len() != 2 {
194	0	return Err(format!("Add expects 2 arguments, got {}", values.len()));
195	0	}
196	0	match (&values[0], &values[1]) {
197	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a + b)),
198	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Float(a + b)),
199	0	(Value::String(a), Value::String(b)) => Ok(Value::String(format!("{a}{b}"))),
200	0	_ => Err(format!(
201	0	"Type error in addition: {:?} + {:?}",
202	0	values[0], values[1]
203	0	)),
204		}
205		}
206
207	0	PrimOp::Sub => match (&values[0], &values[1]) {
208	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a - b)),
209	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Float(a - b)),
210	0	_ => Err("Type error in subtraction".to_string()),
211		},
212
213	0	PrimOp::Mul => match (&values[0], &values[1]) {
214	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Integer(a * b)),
215	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Float(a * b)),
216	0	_ => Err("Type error in multiplication".to_string()),
217		},
218
219	0	PrimOp::Div => match (&values[0], &values[1]) {
220	0	(Value::Integer(a), Value::Integer(b)) => {
221	0	if *b == 0 {
222	0	Err("Division by zero".to_string())
223		} else {
224	0	Ok(Value::Integer(a / b))
225		}
226		}
227	0	(Value::Float(a), Value::Float(b)) => {
228	0	if *b == 0.0 {
229	0	Err("Division by zero".to_string())
230		} else {
231	0	Ok(Value::Float(a / b))
232		}
233		}
234	0	_ => Err("Type error in division".to_string()),
235		},
236
237	0	PrimOp::Mod => match (&values[0], &values[1]) {
238	0	(Value::Integer(a), Value::Integer(b)) => {
239	0	if *b == 0 {
240	0	Err("Modulo by zero".to_string())
241		} else {
242	0	Ok(Value::Integer(a % b))
243		}
244		}
245	0	_ => Err("Type error in modulo".to_string()),
246		},
247
248	0	PrimOp::Pow => match (&values[0], &values[1]) {
249	0	(Value::Integer(a), Value::Integer(b)) => {
250	0	if *b < 0 {
251	0	Err("Negative exponent for integer".to_string())
252		} else {
253	0	Ok(Value::Integer(a.pow(*b as u32)))
254		}
255		}
256	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Float(a.powf(*b))),
257	0	_ => Err("Type error in power".to_string()),
258		},
259
260		// Comparison operations
261	0	PrimOp::Eq => Ok(Value::Bool(values[0] == values[1])),
262
263	0	PrimOp::Ne => Ok(Value::Bool(values[0] != values[1])),
264
265	0	PrimOp::Lt => match (&values[0], &values[1]) {
266	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a < b)),
267	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a < b)),
268	0	_ => Err("Type error in less-than".to_string()),
269		},
270
271	0	PrimOp::Le => match (&values[0], &values[1]) {
272	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a <= b)),
273	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a <= b)),
274	0	_ => Err("Type error in less-equal".to_string()),
275		},
276
277	0	PrimOp::Gt => match (&values[0], &values[1]) {
278	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a > b)),
279	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a > b)),
280	0	_ => Err("Type error in greater-than".to_string()),
281		},
282
283	0	PrimOp::Ge => match (&values[0], &values[1]) {
284	0	(Value::Integer(a), Value::Integer(b)) => Ok(Value::Bool(a >= b)),
285	0	(Value::Float(a), Value::Float(b)) => Ok(Value::Bool(a >= b)),
286	0	_ => Err("Type error in greater-equal".to_string()),
287		},
288
289		// Logical operations
290	0	PrimOp::And => match (&values[0], &values[1]) {
291	0	(Value::Bool(a), Value::Bool(b)) => Ok(Value::Bool(a && b)),
292	0	_ => Err("Type error in AND".to_string()),
293		},
294
295	0	PrimOp::Or => match (&values[0], &values[1]) {
296	0	(Value::Bool(a), Value::Bool(b)) => Ok(Value::Bool(a \|\| b)),
297	0	_ => Err("Type error in OR".to_string()),
298		},
299
300		PrimOp::NullCoalesce => {
301	0	if values.len() != 2 {
302	0	return Err(format!("NullCoalesce expects 2 arguments, got {}", values.len()));
303	0	}
304		// Return left if not nil, otherwise right
305	0	match &values[0] {
306	0	Value::Nil => Ok(values[1].clone()),
307	0	_ => Ok(values[0].clone()),
308		}
309		},
310
311		PrimOp::Not => {
312	0	if values.len() != 1 {
313	0	return Err(format!("NOT expects 1 argument, got {}", values.len()));
314	0	}
315	0	match &values[0] {
316	0	Value::Bool(b) => Ok(Value::Bool(!b)),
317	0	_ => Err("Type error in NOT".to_string()),
318		}
319		}
320
321		// Control flow
322		PrimOp::If => {
323	0	if values.len() != 3 {
324	0	return Err(format!("IF expects 3 arguments, got {}", values.len()));
325	0	}
326
327		// Note: We already evaluated all branches (strict evaluation)
328		// A lazy interpreter would evaluate condition first, then the appropriate branch
329	0	match &values[0] {
330	0	Value::Bool(true) => Ok(values[1].clone()),
331	0	Value::Bool(false) => Ok(values[2].clone()),
332	0	_ => Err("Type error: IF condition must be boolean".to_string()),
333		}
334		}
335
336		// Array operations
337		PrimOp::ArrayNew => {
338		// Create array from all arguments
339	0	Ok(Value::Array(values))
340		}
341
342		PrimOp::ArrayIndex => {
343	0	if values.len() != 2 {
344	0	return Err("Array index expects 2 arguments".to_string());
345	0	}
346	0	match (&values[0], &values[1]) {
347	0	(Value::Array(arr), Value::Integer(idx)) => {
348	0	if idx < 0 \|\| idx as usize >= arr.len() {
349	0	Err(format!("Array index out of bounds: {idx}"))
350		} else {
351	0	Ok(arr[*idx as usize].clone())
352		}
353		}
354	0	_ => Err("Type error in array indexing".to_string()),
355		}
356		}
357
358		PrimOp::ArrayLen => {
359	0	if values.len() != 1 {
360	0	return Err("Array length expects 1 argument".to_string());
361	0	}
362	0	match &values[0] {
363	0	Value::Array(arr) => Ok(Value::Integer(arr.len() as i64)),
364	0	_ => Err("Type error: expected array".to_string()),
365		}
366		}
367
368	0	PrimOp::Concat => Err(format!("Unsupported primitive: {op:?}")),
369		}
370	0	}
371
372		/// Get execution trace for debugging
373		#[must_use]
374	0	pub fn get_trace(&self) -> &[String] {
375	0	&self.trace
376	0	}
377
378		/// Clear the trace
379	0	pub fn clear_trace(&mut self) {
380	0	self.trace.clear();
381	0	}
382		}
383
384		#[cfg(test)]
385		#[allow(clippy::unwrap_used)]
386		mod tests {
387		use super::*;
388		use crate::transpiler::canonical_ast::AstNormalizer;
389		use crate::Parser;
390
391		#[test]
392		fn test_eval_arithmetic() {
393		let input = "1 + 2 * 3";
394		let mut parser = Parser::new(input);
395		let ast = parser.parse().unwrap();
396
397		let mut normalizer = AstNormalizer::new();
398		let core = normalizer.normalize(&ast);
399
400		let mut interp = ReferenceInterpreter::new();
401		let result = interp.eval(&core).unwrap();
402
403		assert_eq!(result, Value::Integer(7)); // 1 + (2 * 3)
404		}
405
406		#[test]
407		fn test_eval_let_binding() {
408		let input = "let x = 10 in ()";
409		let mut parser = Parser::new(input);
410		let ast = parser.parse().unwrap();
411
412		let mut normalizer = AstNormalizer::new();
413		let core = normalizer.normalize(&ast);
414
415		let mut interp = ReferenceInterpreter::new();
416		let result = interp.eval(&core).unwrap();
417
418		// Let with unit body evaluates to unit
419		assert_eq!(result, Value::Unit);
420		}
421
422		#[test]
423		fn test_eval_function() {
424		// This would need more setup to test properly
425		// as we need to handle function definitions and calls
426		}
427		}