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// Simple bidirectional type checking
use crate::ast::*;
pub fn infer(context: Context, expression: Expression) {
todo!();
}
pub fn check(context: Context, expression: Expression) {
todo!();
}
/// Evaluates an expression given a context (of variables) to a term.
/// Panics on non-evaluatable code.
pub fn execute(context: Context, expression: Expression) -> Result<Term, &'static str> {
match expression {
Expression::Annotation { expr, .. } => execute(context, *expr),
Expression::Constant { term } => Ok(term),
Expression::Variable { id } => context.get(&id).ok_or("no such variable in context").map(|x| *x),
Expression::Abstraction { .. } => Err("attempting to execute an abstraction"),
Expression::Application { func, arg } => {
match *func {
Expression::Abstraction { param, func } => {
let result = execute(context.clone(), *arg);
match result {
Ok(value) => {
let mut context = context;
context.insert(param, value);
return execute(context, *func);
},
Err(e) => Err(e)
}
},
_ => Err("attempting to execute an application to nothing")
}
},
Expression::Conditional { if_cond, if_then, if_else } => {
match execute(context.clone(), *if_cond) {
Ok(Term { val: 1, .. }) => execute(context, *if_then),
Ok(Term { val: 0, .. }) => execute(context, *if_else),
_ => Err("invalid type for a conditional")
}
},
}
}
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