From 719c5fad0249911dd4e68b96dab0969abeea515b Mon Sep 17 00:00:00 2001
From: NerdyPepper <akshayoppiliappan@gmail.com>
Date: Sat, 16 Mar 2019 16:16:53 +0530
Subject: use matches, enums

---
 src/main.rs | 112 +++++++++++++++++++++++-------------------------------------
 1 file changed, 43 insertions(+), 69 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 7e2057c..c9d02f7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,82 +1,56 @@
-use std::str;
-
 #[derive(Debug)]
-struct Token {
-    kind: String,
-    val: String,
+enum Token {
+    Operator(char),
+    Num(f64),
+    Paren(char)
 }
 
 fn main() {
-    let input: &str = "2y + 11(1 + 2 + 3) + 12 /    4";
+    let input = "11(12)";
     let input = input.replace(" ", "");
-    println!("{}", input);
 
-    let mut num_vec: String = String::new();
-    let mut char_vec: String = String::new();
+    let lexed = lexer(&input);
 
-    let mut result: Vec<Token> = vec![];
+    println!("{:?}", lexed);
+}
 
+fn lexer(input: &str) -> Result<Vec<Token>, String> {
+    let mut num_vec: String = String::new();
+    let mut result: Vec<Token> = vec![];
     for letter in input.chars() {
-        if letter.is_digit(10) {
-            num_vec.push(letter);
-        } else if letter == '.' {
-            num_vec.push(letter);
-        } else if letter.is_alphabetic() {
-            drain_buffer("Literal", &num_vec[..], &mut result);
-            char_vec.push(letter);
-            num_vec.clear();
-        } else if is_operator(letter) {
-            drain_buffer("Literal", &num_vec[..], &mut result);
-            num_vec.clear();
-            drain_buffer("Variable", &char_vec[..], &mut result);
-            char_vec.clear();
-            result.push(Token { kind: "Operator".into(), val: letter.to_string() });
-        } else if letter == '(' {
-            if char_vec.len() > 0 {
-                drain_buffer("Function", &char_vec[..], &mut result);
-                char_vec.clear();
-            } else if num_vec.len() > 0 {
-                drain_buffer("Literal", &num_vec[..], &mut result);
-                result.push( Token{kind: "Operator".into(), val: "*".to_string()} );
-                num_vec.clear();
+        match letter {
+            '0'...'9' | '.' => {
+                num_vec.push(letter);
+            },
+            '+' | '-' | '/' | '*' | '^' => {
+                let parse_num = num_vec.parse::<f64>().ok();
+                if let Some(x) = parse_num {
+                    result.push(Token::Num(x));
+                    num_vec.clear();
+                }
+                result.push(Token::Paren(letter));
+            },
+            '('  => {
+                let parse_num = num_vec.parse::<f64>().ok();
+                if let Some(x) = parse_num {
+                    result.push(Token::Num(x));
+                    result.push(Token::Operator('*'));
+                    num_vec.clear();
+                }
+                result.push(Token::Paren(letter));
+            },
+            ')' => {
+                let parse_num = num_vec.parse::<f64>().ok();
+                if let Some(x) = parse_num {
+                    result.push(Token::Num(x));
+                    num_vec.clear();
+                }
+                result.push(Token::Paren(letter));
+            }
+            _ => {
+                return Err(format!("Unexpected character: {}", letter))
             }
-            result.push( Token{kind: "Left Paren".into(), val: letter.to_string()} );
-        } else if letter == ')' {
-            drain_buffer("Literal", &num_vec[..], &mut result);
-            num_vec.clear();
-            drain_buffer("Variable", &char_vec[..], &mut result);
-            char_vec.clear();
-            result.push(Token { kind: "Right Paren".into(), val: letter.to_string() });
-        } else if letter == ',' {
-            drain_buffer("Literal", &num_vec[..], &mut result);
-            num_vec.clear();
-            drain_buffer("Variable", &char_vec[..], &mut result);
-            char_vec.clear();
-            result.push(Token { kind: "Function Arg Separator".into(), val: letter.to_string() });
         }
     }
-    drain_buffer("Literal", &num_vec[..], &mut result);
-    num_vec.clear();
-    drain_buffer("Variable", &char_vec[..], &mut result);
-    char_vec.clear();
-    for token in &result {
-        println!("{} => {}", token.kind, token.val);
-    }
-}
-
-fn drain_buffer(k: &str, v: &str, result: &mut Vec<Token>) {
-    if v.len() > 0 {
-        let token = Token {
-            kind: k.into(),
-            val: v.chars().collect::<String>()
-        };
-        result.push(token);
-    }
-}
-
-fn is_operator(x: char) -> bool {
-    match x {
-        '+' | '-' | '/' | '*' | '^' => true,
-        _ => false
-    }
+    Ok(result)
 }
-- 
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