From a050178c692c59861cb0fb9666321fbef7578039 Mon Sep 17 00:00:00 2001
From: NerdyPepper <akshayoppiliappan@gmail.com>
Date: Thu, 21 Mar 2019 10:54:29 +0530
Subject: refactor into modules

---
 src/parse/mod.rs | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 src/parse/mod.rs

(limited to 'src/parse')

diff --git a/src/parse/mod.rs b/src/parse/mod.rs
new file mode 100644
index 0000000..e5c28e6
--- /dev/null
+++ b/src/parse/mod.rs
@@ -0,0 +1,96 @@
+use crate::lex::Token;
+
+pub fn to_postfix(tokens: Vec<Token>) -> Result<Vec<Token>, String> {
+    let mut postfixed: Vec<Token> = vec![];
+    let mut op_stack: Vec<Token> = vec![];
+    for token in tokens {
+        match token {
+            Token::Num(_) => {
+                postfixed.push(token);
+            },
+            Token::Function(_) => {
+                op_stack.push(token);
+            }
+            Token::Operator(current_op) => {
+                while let Some(top_op) = op_stack.last() {
+                    match top_op {
+                        Token::LParen => {
+                            break;
+                        }
+                        Token::Operator(x) => {
+                            let tp = x.precedence;
+                            let cp = current_op.precedence;
+                            if tp > cp || (tp == cp && x.is_left_associative) {
+                                postfixed.push(op_stack.pop().unwrap());
+                            } else {
+                                break;
+                            }
+                        }
+                        Token::Function(_) => {
+                            postfixed.push(op_stack.pop().unwrap());
+                        }
+                        _ => {
+                            return Err(format!("{:?} must not be on operator stack", top_op))
+                        }
+                    }
+                }
+                op_stack.push(token);
+            },
+            Token::LParen => {
+                op_stack.push(token);
+            },
+            Token::RParen => {
+                let mut push_until_paren: bool = false;
+                while let Some(token) = op_stack.pop() {
+                    if token == Token::LParen {
+                        push_until_paren = true;
+                        break;
+                    }
+                    postfixed.push(token)
+                }
+                if !push_until_paren {
+                    return Err(String::from("Mismatched ')'"));
+                }
+            }
+        }
+    }
+    while let Some(op) = op_stack.pop() {
+        postfixed.push(op);
+    }
+    Ok(postfixed)
+}
+
+pub fn eval_postfix(postfixed: Vec<Token>) -> Result<f64, String> {
+    let mut num_stack: Vec<f64> = vec![];
+    for token in postfixed {
+        match token {
+            Token::Num(n) => {
+                num_stack.push(n);
+            },
+            Token::Operator(op) => {
+                if let Some(n2) = num_stack.pop() {
+                    if let Some(n1) = num_stack.pop() {
+                        num_stack.push(op.operate(n1, n2))
+                    } else {
+                        return Err(format!("Too many operators, Too little operands"))
+                    }
+                } else {
+                    return Err(format!("Too many operators, Too little operands"))
+                }
+            },
+            Token::Function(funct) => {
+                if let Some(arg) = num_stack.pop() {
+                    num_stack.push(funct.apply(arg))
+                }
+            }
+            _ => {
+                return Err(format!("Yo nibba how did this get here"))
+            }
+        }
+    }
+    if num_stack.len() == 1 {
+        Ok(num_stack.pop().unwrap())
+    } else {
+        Err(format!("Parser Error"))
+    }
+}
-- 
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