Made it possible for the parser to parse combined variables, eg. xy, so that the user does not have to write the multiplication sign.

src/interpreter.rs

@@ -10,16 +10,6 @@ pub struct Context<'a> {
 
 impl<'a> Context<'a> {
     pub fn new(angle_unit: Unit, symbol_table: &'a mut SymbolTable) -> Self {
-        for constant in prelude::CONSTANTS {
-            symbol_table.insert(
-                constant.0,
-                Stmt::VarDecl(
-                    constant.0.to_string(),
-                    Box::new(Expr::Literal(constant.1.to_string())),
-                ),
-            );
-        }
-
         Context {
             angle_unit: angle_unit.clone(),
             symbol_table,
@@ -119,6 +109,12 @@ fn eval_unit_expr(context: &mut Context, expr: &Expr, kind: &TokenKind) -> Resul
 }
 
 fn eval_var_expr(context: &mut Context, identifier: &str) -> Result<f64, String> {
+    // If there is a constant with this name, return a literal expression with its value
+    if let Some(value) = prelude::CONSTANTS.get(identifier) {
+        return eval_expr(context, &Expr::Literal(value.to_string()));
+    }
+
+    // Look for the variable in the symbol table
     let var_decl = context.symbol_table.get(identifier).cloned();
     match var_decl {
         Some(Stmt::VarDecl(_, expr)) => eval_expr(context, &expr),

src/parser.rs

@@ -121,15 +121,13 @@ fn parse_factor(context: &mut Context) -> Result<Expr, String> {
     while match_token(context, TokenKind::Star)
         || match_token(context, TokenKind::Slash)
         || match_token(context, TokenKind::Identifier)
+        || match_token(context, TokenKind::Literal)
     {
-        let mut op = peek(context).kind.clone();
-
         // If the next token is an identifier, assume it's multiplication. Eg. 3y
-        if let TokenKind::Identifier = op {
-            op = TokenKind::Star;
-        } else {
-            advance(context);
-        }
+        let op = match peek(context).kind {
+            TokenKind::Identifier | TokenKind::Literal => TokenKind::Star,
+            _ => advance(context).kind.clone(),
+        };
 
         let right = parse_unary(context)?;
         left = Expr::Binary(Box::new(left), op, Box::new(right));
@@ -221,7 +219,24 @@ fn parse_identifier(context: &mut Context) -> Result<Expr, String> {
     }
 
     // Eg. x
-    Ok(Expr::Var(identifier.value))
+    if context.symbol_table.contains_var(&identifier.value) {
+        return Ok(Expr::Var(identifier.value));
+    } else {
+        let mut chars = identifier.value.chars();
+        let mut left = Expr::Var(chars.next().unwrap().to_string());
+
+        // Turn each individual character into its own variable reference.
+        // This parses eg `xy` as `x*y` instead of *one* variable.
+        for c in chars {
+            left = Expr::Binary(
+                Box::new(left),
+                TokenKind::Star,
+                Box::new(Expr::Var(c.to_string())),
+            );
+        }
+
+        return Ok(left);
+    }
 }
 
 fn peek<'a>(context: &'a mut Context) -> &'a Token {

src/prelude.rs

@@ -1,14 +1,14 @@
 use FuncType::*;
 
-pub const CONSTANTS: &[(&str, &str)] = &[
-    ("pi", "3.14159265"),
-    ("π", "3.14159265"),
-    ("e", "2.71828182"),
-    ("tau", "6.28318530"),
-    ("τ", "6.28318530"),
-    ("phi", "1.61803398"),
-    ("ϕ", "1.61803398"),
-];
+pub const CONSTANTS: phf::Map<&'static str, &'static str> = phf::phf_map! {
+    "pi" => "3.14159265",
+    "π" => "3.14159265",
+    "e" => "2.71828182",
+    "tau" => "6.28318530",
+    "τ" => "6.28318530",
+    "phi" => "1.61803398",
+    "ϕ" => "1.61803398",
+};
 
 use crate::ast::Unit;
 use funcs::*;

src/symbol_table.rs

@@ -20,9 +20,13 @@ impl SymbolTable {
         self.hashmap.get(key)
     }
 
-    pub fn contains_func(&self, key: &str) -> bool {
-        prelude::UNARY_FUNCS.contains_key(key)
-            || prelude::UNARY_FUNCS.contains_key(key)
-            || self.hashmap.contains_key(&format!("{}()", key))
+    pub fn contains_var(&self, identifier: &str) -> bool {
+        prelude::CONSTANTS.contains_key(identifier) || self.hashmap.contains_key(identifier)
+    }
+
+    pub fn contains_func(&self, identifier: &str) -> bool {
+        prelude::UNARY_FUNCS.contains_key(identifier)
+            || prelude::UNARY_FUNCS.contains_key(identifier)
+            || self.hashmap.contains_key(&format!("{}()", identifier))
     }
 }