From 410af116fe02f515a1741612721ccca41f187b45 Mon Sep 17 00:00:00 2001
From: Bryan Newbold <bnewbold@robocracy.org>
Date: Sat, 23 Oct 2021 17:44:52 -0700
Subject: commit work-in-progress

---
 src/cexpr.rs | 132 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |  19 ++++++++-
 src/sexpr.rs |   4 +-
 3 files changed, 152 insertions(+), 3 deletions(-)
 create mode 100644 src/cexpr.rs

diff --git a/src/cexpr.rs b/src/cexpr.rs
new file mode 100644
index 0000000..bac316c
--- /dev/null
+++ b/src/cexpr.rs
@@ -0,0 +1,132 @@
+/*
+ * Canonical Expressions
+ *
+ * AKA, simplified, normalized algebraic expressions.
+ *
+ */
+
+use crate::sexpr::SExpr;
+
+pub enum NumericConstant {
+    Pi, // 3.141592...
+    E,  // 2.718281...
+    Infinity,
+}
+
+#[derive(Clone, PartialEq)]
+pub enum CNumber {
+    Integer(i64),
+    Rational(i64, u64),
+    // Float
+    // Constant
+}
+
+impl CNumber {
+    pub fn to_sexpr(&self) -> Result<SExpr, String> {
+        match self {
+            CNumber::Integer(v) => Ok(SExpr::SInteger(*v)),
+            CNumber::Rational(a, b) => Ok(SExpr::SList(vec![
+                SExpr::SBuiltin("/".to_string()),
+                SExpr::SInteger(*a),
+                SExpr::SInteger(*b as i64),
+            ])),
+        }
+    }
+}
+
+#[derive(Clone, PartialEq)]
+pub enum CExpr {
+    Symbol(String),
+    Number(CNumber),
+    Sum(Option<CNumber>, Vec<CExpr>),
+    Product(Option<CNumber>, Vec<CExpr>),
+    Power(Box<CExpr>, Box<CExpr>),
+    Factorial(Box<CExpr>),
+    UnaryFunction(String, Box<CExpr>),
+
+    // TODO: Infinity?
+    // TODO: Limit?
+    // TODO: Vector?
+}
+
+impl CExpr {
+
+    pub fn from_sexpr(sexpr: &SExpr) -> Result<CExpr, String> {
+
+        // not all cases are handled; some atoms are covered trivialy
+        match sexpr {
+            SExpr::SNull => Err("null not handled".to_string()),
+            SExpr::STrue | SExpr::SFalse => Err("booleans not handled".to_string()),
+            SExpr::SInteger(v) => Ok(CExpr::Number(CNumber::Integer(*v))),
+            SExpr::SFloat(v) => Err("floats not handled".to_string()),
+            SExpr::SBuiltin(v) => Ok(CExpr::Symbol(v.to_string())),
+            SExpr::SSymbol(v) => Err(format!("symbols (quoted identifiers) not handled: {}", v)),
+            SExpr::SIdentifier(v) => Ok(CExpr::Symbol(v.to_string())),
+            SExpr::SString(_) => Err("null not handled".to_string()),
+            SExpr::SList(_) => Err("null not handled".to_string()),
+            //SExpr::SList(l) => CExpr::from_sexpr_list(l),
+        }
+    }
+
+/*
+    pub fn from_sexpr_list(list: &Vec<SExpr>) -> Result<CExpr, String> {
+        if list.is_empty() {
+            unimplemented!()
+        }
+        match list[0] {
+            SExpr::SBuiltin("+") => {
+                Ok(CExpr::Sum(
+                    // XXX
+                    None,
+                    list[1..].iter().map(|v| CExpr::from_sexpr(v)).collect::<Result<Vec<SExpr>, String>>()?,
+                ))
+            },
+            SExpr::SBuiltin("*") => {
+            },
+            SExpr::SBuiltin("^") => {
+            },
+            _ => {
+                unimplemented!()
+            }
+        }
+    }
+*/
+
+    pub fn new_sum(list: &Vec<SExpr>) -> Result<CExpr, String> {
+        unimplemented!()
+    }
+
+    pub fn new_product(list: &Vec<SExpr>) -> Result<CExpr, String> {
+        unimplemented!()
+    }
+
+    pub fn to_sexpr(&self) -> Result<SExpr, String> {
+        match self {
+            CExpr::Symbol(s) => Ok(SExpr::SIdentifier(s.to_string())),
+            CExpr::Number(n) => n.to_sexpr(),
+            CExpr::Sum(n, l) => Ok(SExpr::SList(vec![
+                SExpr::SBuiltin("+".to_string()),
+                SExpr::SList(l.iter().map(|v| v.to_sexpr()).collect::<Result<Vec<SExpr>, String>>()?),
+                // XXX: n
+            ])),
+            CExpr::Product(n, l) => Ok(SExpr::SList(vec![
+                SExpr::SBuiltin("*".to_string()),
+                SExpr::SList(l.iter().map(|v| v.to_sexpr()).collect::<Result<Vec<SExpr>, String>>()?),
+                // XXX: n
+            ])),
+            CExpr::Power(a, b) => Ok(SExpr::SList(vec![
+                SExpr::SBuiltin("^".to_string()),
+                a.to_sexpr()?,
+                b.to_sexpr()?,
+            ])),
+            CExpr::Factorial(v) => Ok(SExpr::SList(vec![
+                SExpr::SIdentifier("factorial".to_string()),
+                v.to_sexpr()?,
+            ])),
+            CExpr::UnaryFunction(s, v) => Ok(SExpr::SList(vec![
+                SExpr::SIdentifier(s.to_string()),
+                v.to_sexpr()?,
+            ])),
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 6b2bc57..0f67aa4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -5,6 +5,9 @@ use std::io::Write;
 use std::path::Path;
 
 mod sexpr;
+mod cexpr;
+
+use cexpr::CExpr;
 
 fn repl(verbose: bool) {
 
@@ -56,7 +59,21 @@ fn repl(verbose: bool) {
                 continue;
             }
         };
-        println!("{}", sexpr::sexpr_repr(&ast).unwrap());
+        let expr = match CExpr::from_sexpr(&ast) {
+            Ok(v) => v,
+            Err(e) => {
+                println!("couldn't parse as math: {}", e);
+                continue;
+            },
+        };
+        match expr.to_sexpr() {
+            Ok(out) => println!("{}", sexpr::sexpr_repr(&ast).unwrap()),
+            Err(e) => {
+                println!("couldn't return to sexpr: {}", e);
+                continue;
+            },
+
+        }
     }
 }
 
diff --git a/src/sexpr.rs b/src/sexpr.rs
index 6cef563..da1012e 100644
--- a/src/sexpr.rs
+++ b/src/sexpr.rs
@@ -16,9 +16,9 @@ use std::path::Path;
 
 //////////// Types and Constants
 
-const SEXPR_BUILTINS: [&'static str; 14] = [
+const SEXPR_BUILTINS: [&'static str; 15] = [
     "=", ">", ">=", "<", "<=",
-    "+", "-", "*", "/",
+    "+", "-", "*", "/", "^",
     "exp", "log", "sin", "cos", "tan",
     ];
 
-- 
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