149 lines
4.2 KiB
Rust
149 lines
4.2 KiB
Rust
use std::collections::HashMap;
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use parser::AST;
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use parser::AST::*;
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pub struct Environment(pub HashMap<String, AST>);
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type EvalResult = (AST, Environment);
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impl Environment {
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pub fn new() -> Environment {
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Environment(HashMap::new())
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}
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fn add_binding(&mut self, name: String, binding: AST) {
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match *self {
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Environment(ref mut hash_map) => hash_map.insert(name, binding)
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};
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}
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fn lookup_binding(&mut self, name: &String) -> Option<&AST> {
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match *self {
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Environment(ref mut hash_map) => hash_map.get(name)
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}
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}
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pub fn display(&self) {
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match *self {
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Environment(ref hash_map) =>
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for (var, binding) in hash_map {
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println!("{} : {:?}", var, binding);
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}
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}
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println!("----");
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}
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}
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pub fn evaluate(ast: AST, env: Environment) -> (String, Environment) {
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let (reduced_ast, final_env) = reduce((ast, env));
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let output = match reduced_ast {
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DoNothing => "".to_string(),
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Number(n) => format!("{}", n),
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LangString(s) => format!("\"{}\"", s),
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Null => "null".to_string(),
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_ => "not implemented".to_string()
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};
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(output, final_env)
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}
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fn reduce(evr: EvalResult) -> EvalResult {
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let (ast, mut env) = evr;
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match ast {
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IfStatement(if_clause, then_clause, else_clause) => {
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let (condition, new_env) = reduce((*if_clause, env));
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match condition {
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Null => match else_clause {
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Some(cl) => reduce((*cl, new_env)),
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None => (DoNothing, new_env)
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},
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_ => reduce((*then_clause, new_env))
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}
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},
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BinOp(op, lhs, rhs) => {
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let (reduced_lhs, new_env) = reduce((*lhs, env));
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let (reduced_rhs, new_env2) = reduce((*rhs, new_env));
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let result: AST = reduce_binop(*op, reduced_lhs, reduced_rhs);
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(result, new_env2)
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},
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Name(name) => {
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let result = match env.lookup_binding(&name) {
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Some(binding) => match binding {
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&DoNothing => DoNothing,
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&Number(n) => Number(n),
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&LangString(ref s) => LangString(s.clone()),
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&Null => Null,
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_ => panic!("Unreduced ast node for name: {:?}", name)
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},
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None => Null
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};
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(result, env)
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},
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Statements(stmts) => {
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let mut reduced_ast = DoNothing;
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let mut reduced_env = env;
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for stmt in stmts.into_iter() {
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let (new_ast, new_env) = reduce((stmt, reduced_env));
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reduced_env = new_env;
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reduced_ast = new_ast;
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}
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(reduced_ast, reduced_env)
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},
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Binding(name, binding) => {
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let unboxed_binding = *binding;
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let (evaluated_binding, mut evaluated_env) = reduce((unboxed_binding, env));
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evaluated_env.add_binding(name, evaluated_binding);
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(DoNothing, evaluated_env)
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},
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other_ast => (other_ast, env)
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}
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}
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fn reduce_binop(op: AST, lhs: AST, rhs: AST) -> AST {
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macro_rules! LangBool {
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(true) => [Name("true".to_string())];
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(false) => [Name("false".to_string())];
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}
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match (lhs, rhs) {
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(Number(l), Number(r)) => match op {
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Name(ref s) if *s == "+" => Number(l + r),
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Name(ref s) if *s == "-" => Number(l - r),
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Name(ref s) if *s == "*" => Number(l * r),
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Name(ref s) if *s == "/" => if r == 0.0 { Null } else { Number(l / r) },
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Name(ref s) if *s == "==" => if l == r { LangBool!(true) } else { LangBool!(false) },
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Name(ref s) if *s == ">" => if l > r { LangBool!(true) } else { LangBool!(false) },
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Name(ref s) if *s == "<" => if l < r { LangBool!(true) } else { LangBool!(false) },
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_ => Null
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},
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(LangString(s1), LangString(s2)) => match op {
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Name(ref s) if *s == "+" => LangString(format!("{}{}", s1, s2)),
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_ => Null
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},
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_ => Null
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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}
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