diff --git a/.gitignore b/.gitignore
index e3186fa76..ad5684123 100644
--- a/.gitignore
+++ b/.gitignore
@@ -75,6 +75,8 @@ perl/Makefile.config
 
 /src/nix-copy-closure/nix-copy-closure
 
+/src/error-demo/error-demo
+
 /src/build-remote/build-remote
 
 # /tests/
diff --git a/Makefile b/Makefile
index e3057c36c..f6b4a3101 100644
--- a/Makefile
+++ b/Makefile
@@ -16,7 +16,8 @@ makefiles = \
   misc/upstart/local.mk \
   doc/manual/local.mk \
   tests/local.mk \
-  tests/plugins/local.mk
+  tests/plugins/local.mk \
+  src/error-demo/local.mk
 
 -include Makefile.config
 
diff --git a/src/error-demo/error-demo.cc b/src/error-demo/error-demo.cc
new file mode 100644
index 000000000..a9ff6057c
--- /dev/null
+++ b/src/error-demo/error-demo.cc
@@ -0,0 +1,66 @@
+#include "error.hh"
+#include "nixexpr.hh"
+
+#include <iostream>
+#include <optional>
+
+int main()
+{
+    using namespace nix;
+
+    // In each program where errors occur, this has to be set.
+    ErrorInfo::programName = std::optional("error-demo");
+
+    // Error in a program; no hint and no nix code.
+    printErrorInfo(
+        ErrorInfo { .level = elError,
+                    .name = "name",
+                    .description = "error description",
+                  });
+
+    // Warning with name, description, and hint.
+    // The hintfmt function makes all the substituted text yellow.
+    printErrorInfo(
+        ErrorInfo { .level = elWarning,
+                    .name = "name",
+                    .description = "error description",
+                    .hint =  std::optional(
+                                 hintfmt("there was a %1%", "warning")),
+                  });
+
+
+    // Warning with nix file, line number, column, and the lines of
+    // code where a warning occurred.
+    SymbolTable testTable;
+    auto problem_file = testTable.create("myfile.nix");
+
+    printErrorInfo(
+        ErrorInfo{
+            .level = elWarning,
+            .name = "warning name",
+            .description = "warning description",
+            .hint = hintfmt("this hint has %1% templated %2%!!", "yellow", "values"),
+            .nixCode = NixCode {
+                .errPos = Pos(problem_file, 40, 13),
+                .prevLineOfCode = std::nullopt,
+                .errLineOfCode = "this is the problem line of code",
+                .nextLineOfCode = std::nullopt
+            }});
+
+    // Error with previous and next lines of code.
+    printErrorInfo(
+        ErrorInfo{
+            .level = elError,
+            .name = "error name",
+            .description = "error description",
+            .hint = hintfmt("this hint has %1% templated %2%!!", "yellow", "values"),
+            .nixCode = NixCode {
+                .errPos = Pos(problem_file, 40, 13),
+                .prevLineOfCode = std::optional("previous line of code"),
+                .errLineOfCode = "this is the problem line of code",
+                .nextLineOfCode = std::optional("next line of code"),
+            }});
+
+
+    return 0;
+}
diff --git a/src/error-demo/local.mk b/src/error-demo/local.mk
new file mode 100644
index 000000000..2c528490a
--- /dev/null
+++ b/src/error-demo/local.mk
@@ -0,0 +1,12 @@
+programs += error-demo
+
+error-demo_DIR := $(d)
+
+error-demo_SOURCES := \
+  $(wildcard $(d)/*.cc) \
+
+error-demo_CXXFLAGS += -I src/libutil -I src/libexpr
+
+error-demo_LIBS = libutil libexpr
+
+error-demo_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -lboost_context -lboost_thread -lboost_system
diff --git a/src/libutil/ansicolor.hh b/src/libutil/ansicolor.hh
new file mode 100644
index 000000000..390bd4d17
--- /dev/null
+++ b/src/libutil/ansicolor.hh
@@ -0,0 +1,13 @@
+#pragma once 
+
+namespace nix 
+{
+  /* Some ANSI escape sequences. */
+  #define ANSI_NORMAL "\e[0m"
+  #define ANSI_BOLD "\e[1m"
+  #define ANSI_FAINT "\e[2m"
+  #define ANSI_RED "\e[31;1m"
+  #define ANSI_GREEN "\e[32;1m"
+  #define ANSI_YELLOW "\e[33;1m"
+  #define ANSI_BLUE "\e[34;1m"
+}
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
new file mode 100644
index 000000000..a5571d4ec
--- /dev/null
+++ b/src/libutil/error.cc
@@ -0,0 +1,146 @@
+#include "error.hh"
+
+#include <iostream>
+#include <optional>
+
+namespace nix
+{
+
+std::optional<string> ErrorInfo::programName = std::nullopt;
+
+std::ostream& operator<<(std::ostream &os, const hintformat &hf)
+{
+    return os << hf.str();
+}
+
+string showErrPos(const ErrPos &errPos)
+{
+    if (errPos.column > 0) {
+        return fmt("(%1%:%2%)", errPos.lineNumber, errPos.column);
+    } else {
+        return fmt("(%1%)", errPos.lineNumber);
+    };
+}
+
+void printCodeLines(const string &prefix, const NixCode &nixCode)
+{
+    // previous line of code.
+    if (nixCode.prevLineOfCode.has_value()) {
+        std::cout << fmt("%1% %|2$5d|| %3%",
+                         prefix,
+                         (nixCode.errPos.lineNumber - 1),
+                         *nixCode.prevLineOfCode)
+                  << std::endl;
+    }
+
+    // line of code containing the error.%2$+5d%
+    std::cout << fmt("%1% %|2$5d|| %3%",
+                     prefix,
+                     (nixCode.errPos.lineNumber),
+                     nixCode.errLineOfCode)
+              << std::endl;
+
+    // error arrows for the column range.
+    if (nixCode.errPos.column > 0) {
+        int start = nixCode.errPos.column;
+        std::string spaces;
+        for (int i = 0; i < start; ++i) {
+            spaces.append(" ");
+        }
+
+        std::string arrows("^");
+
+        std::cout << fmt("%1%      |%2%" ANSI_RED "%3%" ANSI_NORMAL,
+                         prefix,
+                         spaces,
+                         arrows) << std::endl;
+    }
+
+    // next line of code.
+    if (nixCode.nextLineOfCode.has_value()) {
+        std::cout << fmt("%1% %|2$5d|| %3%",
+                         prefix,
+                         (nixCode.errPos.lineNumber + 1),
+                         *nixCode.nextLineOfCode)
+                  << std::endl;
+    }
+}
+
+void printErrorInfo(const ErrorInfo &einfo)
+{
+    int errwidth = 80;
+    string prefix = "    ";
+
+    string levelString;
+    switch (einfo.level) {
+    case ErrLevel::elError: {
+        levelString = ANSI_RED;
+        levelString += "error:";
+        levelString += ANSI_NORMAL;
+        break;
+    }
+    case ErrLevel::elWarning: {
+        levelString = ANSI_YELLOW;
+        levelString += "warning:";
+        levelString += ANSI_NORMAL;
+        break;
+    }
+    default: {
+        levelString = fmt("invalid error level: %1%", einfo.level);
+        break;
+    }
+    }
+
+    int ndl = prefix.length() + levelString.length() + 3 + einfo.name.length() + einfo.programName.value_or("").length();
+    int dashwidth = ndl > (errwidth - 3) ? 3 : errwidth - ndl;
+
+    string dashes;
+    for (int i = 0; i < dashwidth; ++i)
+        dashes.append("-");
+
+    // divider.
+    std::cout << fmt("%1%%2%" ANSI_BLUE " %3% %4% %5% %6%" ANSI_NORMAL,
+                     prefix,
+                     levelString,
+                     "---",
+                     einfo.name,
+                     dashes,
+                     einfo.programName.value_or(""))
+              << std::endl;
+
+    // filename.
+    if (einfo.nixCode.has_value()) {
+        if (einfo.nixCode->errPos.nixFile != "") {
+            string eline = einfo.nixCode->errLineOfCode != ""
+                           ? string(" ") + showErrPos(einfo.nixCode->errPos)
+                           : "";
+
+            std::cout << fmt("%1%in file: " ANSI_BLUE "%2%%3%" ANSI_NORMAL,
+                             prefix, 
+                             einfo.nixCode->errPos.nixFile,
+                             eline) << std::endl;
+            std::cout << prefix << std::endl;
+        } else {
+            std::cout << fmt("%1%from command line argument", prefix) << std::endl;
+            std::cout << prefix << std::endl;
+        }
+    }
+
+    // description
+    std::cout << prefix << einfo.description << std::endl;
+    std::cout << prefix << std::endl;
+
+    // lines of code.
+    if (einfo.nixCode->errLineOfCode != "") {
+        printCodeLines(prefix, *einfo.nixCode);
+        std::cout << prefix << std::endl;
+    }
+
+    // hint
+    if (einfo.hint.has_value()) {
+        std::cout << prefix << *einfo.hint << std::endl;
+        std::cout << prefix << std::endl;
+    }
+}
+
+}
diff --git a/src/libutil/error.hh b/src/libutil/error.hh
new file mode 100644
index 000000000..f402b692e
--- /dev/null
+++ b/src/libutil/error.hh
@@ -0,0 +1,121 @@
+#ifndef error_hh
+#define error_hh
+
+#include "ansicolor.hh"
+#include <string>
+#include <optional>
+#include <iostream>
+#include "types.hh"
+
+namespace nix
+{
+
+typedef enum {
+    elWarning,
+    elError
+} ErrLevel;
+
+struct ErrPos
+{
+    int lineNumber;
+    int column;
+    string nixFile;
+
+    template <class P>
+    ErrPos& operator=(const P &pos)
+    {
+        lineNumber = pos.line;
+        column = pos.column;
+        nixFile = pos.file;
+        return *this;
+    }
+
+    template <class P>
+    ErrPos(const P &p)
+    {
+      *this = p;
+    }
+};
+
+struct NixCode
+{
+    ErrPos errPos;
+    std::optional<string> prevLineOfCode;
+    string errLineOfCode;
+    std::optional<string> nextLineOfCode;
+};
+
+// ----------------------------------------------------------------
+// format function for hints.  same as fmt, except templated values
+// are always in yellow.
+
+template <class T>
+struct yellowify
+{
+    yellowify(T &s) : value(s) {}
+    T &value;
+};
+
+template <class T>
+std::ostream& operator<<(std::ostream &out, const yellowify<T> &y)
+{
+    return out << ANSI_YELLOW << y.value << ANSI_NORMAL;
+}
+
+class hintformat
+{
+public:
+    hintformat(string format) :fmt(format)
+    {
+        fmt.exceptions(boost::io::all_error_bits ^ boost::io::too_many_args_bit);
+    }
+    template<class T>
+    hintformat& operator%(const T &value)
+    {
+        fmt % yellowify(value);
+        return *this;
+    }
+
+    std::string str() const
+    {
+        return fmt.str();
+    }
+
+    template <typename U>
+    friend class AddHint;
+private:
+    format fmt;
+};
+
+std::ostream& operator<<(std::ostream &os, const hintformat &hf);
+
+template<typename... Args>
+inline hintformat hintfmt(const std::string & fs, const Args & ... args)
+{
+    hintformat f(fs);
+    formatHelper(f, args...);
+    return f;
+}
+
+// -------------------------------------------------
+// ErrorInfo.
+struct ErrorInfo
+{
+    ErrLevel level;
+    string name;
+    string description;
+    std::optional<hintformat> hint;
+    std::optional<NixCode> nixCode;
+
+    static std::optional<string> programName;
+};
+
+// --------------------------------------------------------
+// error printing
+
+// just to cout for now.
+void printErrorInfo(const ErrorInfo &einfo);
+
+}
+
+#endif
diff --git a/src/libutil/types.hh b/src/libutil/types.hh
index a1ce7b372..250c9581d 100644
--- a/src/libutil/types.hh
+++ b/src/libutil/types.hh
@@ -41,7 +41,8 @@ struct FormatOrString
 {
     string s;
     FormatOrString(const string & s) : s(s) { };
-    FormatOrString(const format & f) : s(f.str()) { };
+    template<class F>
+    FormatOrString(const F & f) : s(f.str()) { };
     FormatOrString(const char * s) : s(s) { };
 };
 
@@ -51,12 +52,13 @@ struct FormatOrString
    ... a_n’. However, ‘fmt(s)’ is equivalent to ‘s’ (so no %-expansion
    takes place). */
 
-inline void formatHelper(boost::format & f)
+template<class F>
+inline void formatHelper(F & f)
 {
 }
 
-template<typename T, typename... Args>
-inline void formatHelper(boost::format & f, const T & x, const Args & ... args)
+template<class F, typename T, typename... Args>
+inline void formatHelper(F & f, const T & x, const Args & ... args)
 {
     formatHelper(f % x, args...);
 }
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 815b1f288..8e24ef968 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -2,6 +2,8 @@
 
 #include "types.hh"
 #include "logging.hh"
+#include "ansicolor.hh"
+#include "error.hh"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -446,15 +448,6 @@ std::string shellEscape(const std::string & s);
 void ignoreException();
 
 
-/* Some ANSI escape sequences. */
-#define ANSI_NORMAL "\e[0m"
-#define ANSI_BOLD "\e[1m"
-#define ANSI_FAINT "\e[2m"
-#define ANSI_RED "\e[31;1m"
-#define ANSI_GREEN "\e[32;1m"
-#define ANSI_YELLOW "\e[33;1m"
-#define ANSI_BLUE "\e[34;1m"
-
 
 /* Tree formatting. */
 constexpr char treeConn[] = "├───";