Refactoring
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greg
parent
60644ba3d7
commit
8493233b69
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@ -71,14 +71,12 @@ impl EvaluatorState {
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fn eval(&mut self, expr: Sexp) -> Result<Sexp, String> {
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use self::Sexp::*;
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Ok(match expr {
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SymbolAtom(ref sym) => {
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match self.get_var(sym) {
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Some(ref sexp) => {
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let q: &Sexp = sexp; //WTF? if I delete this line, the copy doesn't work??
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q.clone() //TODO make this not involve a clone
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},
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None => return Err(format!("Variable {} not bound", sym)),
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}
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SymbolAtom(ref sym) => match self.get_var(sym) {
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Some(ref sexp) => {
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let q: &Sexp = sexp; //WTF? if I delete this line, the copy doesn't work??
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q.clone() //TODO make this not involve a clone
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},
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None => return Err(format!("Variable {} not bound", sym)),
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},
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expr @ StringAtom(_) => expr,
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expr @ NumberAtom(_) => expr,
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@ -86,70 +84,85 @@ impl EvaluatorState {
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False => False,
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Cons(box operator, box operands) => {
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match operator {
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SymbolAtom(ref sym) => match &sym[..] {
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"quote" => operands,
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"eq?" => match operands {
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Cons(box lhs, box Cons(box rhs, _)) => {
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match lhs == rhs {
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true => True,
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false => False,
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}
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},
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_ => True,
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},
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"cons" => match operands {
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Cons(box cadr, box Cons(box caddr, box Nil)) => {
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let newl = self.eval(cadr)?;
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let newr = self.eval(caddr)?;
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Cons(Box::new(newl), Box::new(newr))
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},
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_ => return Err(format!("Bad arguments for cons")),
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},
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"car" => match operands {
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Cons(box car, _) => car,
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_ => return Err(format!("called car with a non-pair argument")),
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},
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"cdr" => match operands {
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Cons(_, box cdr) => cdr,
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_ => return Err(format!("called cdr with a non-pair argument")),
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},
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"atom?" => match operands {
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Cons(_, _) => False,
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_ => True,
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},
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"define" => match operands {
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Cons(box SymbolAtom(sym), box Cons(box expr, box Nil)) => {
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let evaluated = self.eval(expr)?;
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self.set_var(sym, evaluated);
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Nil
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},
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_ => return Err(format!("Bad assignment")),
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SymbolAtom(sym) => match &sym[..] {
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"quote" | "eq?" | "cons" | "car" | "cdr" | "atom?" |
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"define" | "lambda" | "if" | "cond" => self.eval_special_form(&sym[..], operands)?,
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_ => {
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let evaled = self.eval(SymbolAtom(sym))?;
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self.apply(evaled, operands)?
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}
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"lambda" => match operands {
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Cons(box paramlist, box Cons(box formalexp, box Nil)) => {
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unimplemented!() //needs to return an abstract object
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},
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_ => return Err(format!("Bad lambda expression")),
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},
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"if" => match operands {
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Cons(box test, box body) => {
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let truth_value = test.truthy();
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match (truth_value, body) {
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(true, Cons(box consequent, _)) => consequent,
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(false, Cons(_, box Cons(box alternative, _))) => alternative,
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_ => return Err(format!("Bad if expression"))
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}
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},
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_ => return Err(format!("Bad if expression"))
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},
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_ => unimplemented!(),
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},
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other => {println!("OTHER? {:?}", other); unimplemented!() }
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_ => unimplemented!()
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}
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},
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Nil => Nil,
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})
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}
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fn eval_special_form(&mut self, form: &str, operands: Sexp) -> Result<Sexp, String> {
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use self::Sexp::*;
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Ok(match form {
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"quote" => operands,
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"eq?" => match operands {
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Cons(box lhs, box Cons(box rhs, _)) => {
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match lhs == rhs {
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true => True,
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false => False,
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}
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},
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_ => True,
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},
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"cons" => match operands {
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Cons(box cadr, box Cons(box caddr, box Nil)) => {
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let newl = self.eval(cadr)?;
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let newr = self.eval(caddr)?;
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Cons(Box::new(newl), Box::new(newr))
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},
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_ => return Err(format!("Bad arguments for cons")),
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},
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"car" => match operands {
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Cons(box car, _) => car,
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_ => return Err(format!("called car with a non-pair argument")),
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},
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"cdr" => match operands {
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Cons(_, box cdr) => cdr,
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_ => return Err(format!("called cdr with a non-pair argument")),
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},
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"atom?" => match operands {
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Cons(_, _) => False,
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_ => True,
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},
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"define" => match operands {
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Cons(box SymbolAtom(sym), box Cons(box expr, box Nil)) => {
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let evaluated = self.eval(expr)?;
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self.set_var(sym, evaluated);
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Nil
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},
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_ => return Err(format!("Bad assignment")),
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}
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"lambda" => match operands {
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Cons(box paramlist, box Cons(box formalexp, box Nil)) => {
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unimplemented!() //needs to return an abstract object
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},
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_ => return Err(format!("Bad lambda expression")),
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},
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"if" => match operands {
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Cons(box test, box body) => {
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let truth_value = test.truthy();
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match (truth_value, body) {
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(true, Cons(box consequent, _)) => consequent,
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(false, Cons(_, box Cons(box alternative, _))) => alternative,
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_ => return Err(format!("Bad if expression"))
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}
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},
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_ => return Err(format!("Bad if expression"))
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},
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_ => unimplemented!(),
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})
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}
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fn apply(&mut self, function: Sexp, operands: Sexp) -> Result<Sexp, String> {
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Err(format!("Not implemented"))
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}
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}
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fn read(input: &str) -> Result<Vec<Sexp>, String> {
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