From 1c230933c1763a0792141377d7cb45734b8abfbb Mon Sep 17 00:00:00 2001
From: Srajan Garg <srajan.garg@gmail.com>
Date: Wed, 20 Jan 2016 23:07:55 +0530
Subject: [PATCH] added support for symbols, and respective tests

---
 symengine/parser.cpp                  | 43 +++++++++++++++++++++------
 symengine/tests/basic/test_parser.cpp | 41 ++++++++++++++++++++++++-
 2 files changed, 74 insertions(+), 10 deletions(-)

diff --git a/symengine/parser.cpp b/symengine/parser.cpp
index 559d2687ec..ce0cd35e45 100644
--- a/symengine/parser.cpp
+++ b/symengine/parser.cpp
@@ -39,16 +39,24 @@ class expressionParser
     {
         RCP<const Basic> result;
         bool result_set = false;
+        bool expr_is_symbol = false;
         std::string expr;
 
         for (uint iter = l; iter < h; ++iter)
         {
-            if (OPERATORS.find(s[iter]) != OPERATORS.end())
+            if (is_operator(s, iter))
             {
                 if (s[iter] != '(')
+                {
                     if (!result_set)
-                        result = integer(std::stoi(expr));
-                
+                    {
+                        if (expr_is_symbol)
+                            result = symbol(expr);
+                        else
+                            result = integer(std::stoi(expr));
+                    }
+                }
+
                 switch(s[iter])
                 {
                     case '+':
@@ -79,13 +87,23 @@ class expressionParser
                         continue;
                 }
                 result_set = true;
+                expr_is_symbol = false;
             }
             else
             {
                 expr += s[iter];
 
+                int ascii = s[iter] - '0';
+                if (ascii < 0 or ascii > 9)
+                    expr_is_symbol = true;
+
                 if (iter == h-1)
-                    result = integer(std::stoi(expr));
+                {
+                    if (expr_is_symbol)
+                        result = symbol(expr);
+                    else
+                        result = integer(std::stoi(expr));
+                }
             }
         }
 
@@ -95,7 +113,6 @@ class expressionParser
     RCP<const Basic> parse(std::string &s)
     {
         std::string copy;
-        char x;
         std::stack<uint> rBracket;
         std::stack<std::pair<int, uint> > opStack;
 
@@ -113,9 +130,9 @@ class expressionParser
 
         for (int i = newLength-1; i >= 0; i--)
         {
-            x = copy[i];
-            if (OPERATORS.find(x) != OPERATORS.end())
-            {   
+            if (is_operator(copy, i))
+            {
+                char x = copy[i];
                 if(x == '(')
                 {
                     while(opStack.top().second != rBracket.top())
@@ -127,7 +144,7 @@ class expressionParser
                 else if(x == ')')
                 {
                     opStack.push(std::make_pair(opPrecedence[x], i));
-                    rBracket.push(i);           
+                    rBracket.push(i);        
                 }
                 else
                 {
@@ -141,6 +158,14 @@ class expressionParser
         }
         return parse_string(copy, 0, newLength);
     }
+
+    bool is_operator(std::string& s, int iter)
+    {
+        if (iter >= 0 and iter < (int)s.length())
+            if (OPERATORS.find(s[iter]) != OPERATORS.end())
+                return true;
+        return false;
+    }
 };
 
 } // SymEngine
diff --git a/symengine/tests/basic/test_parser.cpp b/symengine/tests/basic/test_parser.cpp
index 257b52e2c5..cc468cca48 100644
--- a/symengine/tests/basic/test_parser.cpp
+++ b/symengine/tests/basic/test_parser.cpp
@@ -42,7 +42,7 @@ TEST_CASE("Parsing: integers, basic operations", "[parser]")
     s = "((3)+(1*0))";
     res = p.parse(s);
     REQUIRE(eq(*res, *integer(3)));
-    
+
     s = "((2))*(1+(2*3))";
     res = p.parse(s);
     REQUIRE(eq(*res, *integer(14)));
@@ -83,3 +83,42 @@ TEST_CASE("Parsing: integers, basic operations", "[parser]")
     res = p.parse(s);
     REQUIRE(eq(*res, *add(integer(9), div(integer(-5), integer(4)))));
 }
+
+TEST_CASE("Parsing: symbols", "[parser]")
+{
+    std::string s;
+    expressionParser p;
+    RCP<const Basic> res;
+    RCP<const Basic> x = symbol("x");
+    RCP<const Basic> y = symbol("y");
+    RCP<const Basic> w = symbol("w1");
+    RCP<const Basic> l = symbol("l0ngn4me");
+
+    s = "x + 2*y";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *add(x, mul(integer(2), y))));
+
+    s = "w1*y";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *mul(w ,y)));
+
+    s = "x^(3+w1)-2/y";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *add(pow(x, add(integer(3), w)), div(integer(-2), y))));
+
+    s = "l0ngn4me - w1*y + 2^(x)";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *add(add(l, neg(mul(w, y))), pow(integer(2), x))));
+
+    s = "4*x/8 - (w1*y)";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *add(neg(mul(w, y)), div(x, integer(2)))));
+
+    s = "3*y + (2*y)";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *mul(y, integer(5))));
+
+    s = "3*y/(1+x)";
+    res = p.parse(s);
+    REQUIRE(eq(*res, *div(mul(y, integer(3)), add(x, integer(1)))));
+}