4 files changed, 54 insertions, 29 deletions

diff --git a/rust/src/ast.rs b/rust/src/ast.rs
new file mode 100644
index 0000000..b179704
--- /dev/null
+++ b/rust/src/ast.rs
@@ -0,0 +1,18 @@
+use std::fmt::{self, Display};
+
+#[derive(Debug, PartialEq)]
+pub enum Value {
+    Num(i32),
+    Bool(bool),
+    Sym(String),
+}
+
+impl Display for Value {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Value::Num(i) => write!(f, "{}", i),
+            Value::Bool(b) => write!(f, "{}", b),
+            Value::Sym(s) => write!(f, "{}", s),
+        }
+    }
+}
diff --git a/rust/src/lambda.rs b/rust/src/lambda.rs
index 8c4c640..18568d7 100644
--- a/rust/src/lambda.rs
+++ b/rust/src/lambda.rs
@@ -1,7 +1,10 @@
-use std::{
-    fmt::{self, Display},
-    fs::read_to_string,
-};
+use std::fs::read_to_string;
+
+mod ast;
+use ast::*;
+
+mod parser;
+use parser::*;
 
 pub fn run(arg: &str) -> String {
     let content = read_to_string(arg).unwrap();
@@ -10,30 +13,9 @@ pub fn run(arg: &str) -> String {
     result.to_string()
 }
 
-#[derive(Debug, PartialEq)]
-pub enum Value {
-    Num(i32),
-    Bool(bool),
-    Sym(String),
-}
-
-impl Display for Value {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Value::Num(i) => write!(f, "{}", i),
-            Value::Bool(b) => write!(f, "{}", b),
-            Value::Sym(s) => write!(f, "{}", s),
-        }
-    }
-}
-
 fn interpret(arg: &str) -> Value {
-    let token = arg.trim();
-    token
-        .parse::<i32>()
-        .map(Value::Num)
-        .or(token.parse::<bool>().map(Value::Bool))
-        .unwrap_or(Value::Sym(token.to_string()))
+    // interpreting a value is the value itself
+    parse(arg)
 }
 
 #[cfg(test)]
diff --git a/rust/src/main.rs b/rust/src/main.rs
index b6cc9bf..f401886 100644
--- a/rust/src/main.rs
+++ b/rust/src/main.rs
@@ -2,8 +2,6 @@ use std::env::args;
 
 use lambda::run;
 
-mod lambda;
-
 fn main() {
     run(&args().nth(1).unwrap());
 }
diff --git a/rust/src/parser.rs b/rust/src/parser.rs
new file mode 100644
index 0000000..d5d4c30
--- /dev/null
+++ b/rust/src/parser.rs
@@ -0,0 +1,27 @@
+use crate::ast::*;
+
+pub fn parse(arg: &str) -> Value {
+    let token = arg.trim();
+    parse_number(token)
+        .or(parse_bool(token))
+        .or(parse_symbol(token))
+        .unwrap()
+}
+
+fn parse_symbol(token: &str) -> Result<Value, String> {
+    Ok(Value::Sym(token.to_string()))
+}
+
+fn parse_bool(token: &str) -> Result<Value, String> {
+    token
+        .parse::<bool>()
+        .map(Value::Bool)
+        .map_err(|e| e.to_string())
+}
+
+fn parse_number(token: &str) -> Result<Value, String> {
+    token
+        .parse::<i32>()
+        .map(Value::Num)
+        .map_err(|e| e.to_string())
+}