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commit 82d7ddb2f105a21787d0d67b499dd8f7068d9d40 (HEAD -> master, tag: task3-1)
Author: junniboi <junniboi@vt.edu>
Date:   Wed Aug 29 17:24:13 2018 -0400

    Worked on task 3 : added e, sqrt, exponents, natural log.

diff --git a/environment.cpp b/environment.cpp
index 22a7c8d..42f883d 100644
--- a/environment.cpp
+++ b/environment.cpp
@@ -104,6 +104,72 @@ Expression div(const std::vector<Expression> & args){
   return Expression(result);
 };
 
+//compute the exponent. 1st input is base and 2nd is the exponent 
+Expression exponent(const std::vector<Expression>& args) {
+	
+	double result = 0;
+
+	if (nargs_equal(args, 2))
+	{
+		if ((args[0].isHeadNumber()) && (args[1].isHeadNumber()))
+			result = pow(args[0].head().asNumber(), args[1].head().asNumber());
+		else
+			throw SemanticError("Error in call to exponent: invalid argument.");
+	}
+	else
+		throw SemanticError("Error in call to exponent: invalid number of arguments.");
+
+	return Expression(result);
+};
+
+Expression sqrt(const std::vector<Expression> & args) {
+
+	double result = 0;
+
+	if (nargs_equal(args, 1)) 
+	{
+		if (args[0].isHeadNumber())
+		{
+			if (args[0].head().asNumber() >= 0)
+				result = sqrt(args[0].head().asNumber());
+
+			else
+				throw SemanticError("Error in call to square root: input has to be positive.");
+
+		}
+		else
+			throw SemanticError("Error in call to sqaure root: number argument must be one.");
+	}
+	else
+		throw SemanticError("Error in call to sqaure root: invalid argument.");
+
+	return Expression(result);
+};
+
+// computes the natural log
+Expression ln(const std::vector<Expression> & args) {
+
+	double result = 0;
+
+	if (nargs_equal(args, 1))
+	{
+		if (args[0].isHeadNumber())
+		{
+			if (args[0].head().asNumber() >= 0)
+				result = log(args[0].head().asNumber());
+
+			else
+				throw SemanticError("Error in call to natural log: input has to be positive.");
+		}
+		else
+			throw SemanticError("Error in call to natural log: number argument must be one.");
+	}
+	else
+		throw SemanticError("Error in call to natural log: invalid argument.");
+
+	return Expression(result);
+};
+
 const double PI = std::atan2(0, -1);
 const double EXP = std::exp(1);
 
@@ -196,4 +262,17 @@ void Environment::reset(){
 
   // Procedure: div;
   envmap.emplace("/", EnvResult(ProcedureType, div)); 
+
+  //milestone 0
+  // task 3-1 Built-in value of e = exp(1)
+  envmap.emplace("e", EnvResult(ExpressionType, Expression(EXP)));
+
+  // task 3-2 procedure: sqrt
+  envmap.emplace("sqrt", EnvResult(ProcedureType, sqrt));
+
+  // task 3-3 precedure: exponent
+  envmap.emplace("^", EnvResult(ProcedureType, exponent));
+
+  // task 3-4 procedure: natural log 
+  envmap.emplace("ln", EnvResult(ProcedureType, ln));
 }