95 lines
2.5 KiB
Rust
95 lines
2.5 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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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 (mut 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 (mut ast, mut env) = evr;
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match ast {
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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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