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Add concept of Null expression 

Finally, the null-only behavior is starting to manifest itself!
This commit is contained in:
greg 2016-01-21 19:12:07 -08:00
parent 15d4317191
commit e9dd0d9ae8
1 changed files with 3 additions and 2 deletions
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5
src/eval.rs
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@ -56,6 +56,7 @@ impl Evaluable for Expression {
fn is_reducible(&self) -> bool {
use parser::Expression::*;
match *self {
Null => false,
StringLiteral(_) => false,
Number(_) => false,
_ => true,
@ -123,11 +124,11 @@ impl Evaluator {
match &op[..] {
"+" => match (left, right) {
(Number(l), Number(r)) => Number(l + r),
_ => unimplemented!(),
_ => Null,
},
"-" => match (left, right) {
(Number(l), Number(r)) => Number(l - r),
_ => unimplemented!(),
_ => Null,
},
"=" => match (left, right) {
_ => unimplemented!()