add functions and variables to language

src/commands/eval/mod.rs

@@ -1,5 +1,8 @@
 use crate::common::{Context, Error};
 
+use std::collections::HashMap;
+use std::borrow::Cow;
+
 mod tokenizer;
 mod parse;
 
@@ -7,9 +10,17 @@ fn evaluate(expr: &str) -> Result<f64, Error> {
     let tokens = tokenizer::Token::tokenize(expr)?;
     let mut tokens = tokens.iter();
 
-    let tree = parse::ParseTree::new(&mut tokens)?;
+    let globals = HashMap::new();
+    let locals = HashMap::new();
+    let mut locals = Cow::Borrowed(&locals);
 
-    Ok(tree.evaluate())
+    let tree = parse::ParseTree::parse(&mut tokens, &globals, &mut locals)?;
+
+    let mut globals = HashMap::new();
+    let locals = HashMap::new();
+    let mut locals = Cow::Borrowed(&locals);
+
+    tree.evaluate(&mut globals, &mut locals)
 }
 
 /// Evaluates an expression (uses Polish Notation)