2 files changed, 97 insertions, 0 deletions
diff --git a/src/error-demo/error-demo.cc b/src/error-demo/error-demo.cc
new file mode 100644
index 000000000..8fb20d38c
--- /dev/null
+++ b/src/error-demo/error-demo.cc
@@ -0,0 +1,87 @@
+#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");
+
+    // There are currently four error types:
+    //
+    // 			ProgramError, ProgramWarning, NixLangError, NixLangWarning.
+    //
+    // Each error type is created with a specific sequence of builder functions.
+    // Unlike with a constructor, each parameter is clearly named.
+    // If the sequence of function calls isn't followed, then there's a type
+    // error. This should make for a consistent look in the code when errors are
+    // created.
+
+    // ProgramError takes name, description, and an optional hint.
+    printErrorInfo( ProgramError()
+                    .name("name")
+                    .description("error description")
+                    .nohint()
+                  );
+
+    // ProgramWarning takes name, description, and an optional hint.
+    // The hint is in the form of a hintfmt class, which wraps boost::format(),
+    // and makes all the substituted text yellow.
+    printErrorInfo( ProgramWarning()
+                    .name("warning name")
+                    .description("warning description")
+                    // the templated value, 'warning', is automatically colored yellow.
+                    .hint(hintfmt("there was a %1%", "warning")) 
+                  );
+
+    /*
+      // some invalid errors:
+
+      // type error: no hint function.
+      ProgramError()
+        .name("name")
+        .description("error description");
+
+      // type error:  description before name.
+      ProgramError()
+        .description("error description")
+        .name("name")
+        .nohint();
+
+      // type error: hint function with regular boost format, not special
+      hintfmt. ProgramError() .description("error description") .name("name")
+        .hint(format("there was a %1%") % "warning");
+    */
+
+    // NixLangWarning adds nix file, line number, column range, and the lines of
+    // code where a warning occurred.
+
+    SymbolTable testTable;
+    auto problem_symbol = testTable.create("problem");
+
+    printErrorInfo(NixLangWarning()
+                   .name("warning name")
+                   .description("warning description")
+                   .pos(Pos(problem_symbol, 40, 13))
+                   .linesOfCode(std::nullopt,
+                                "this is the problem line of code",
+                                std::nullopt)
+                   .hint(hintfmt("this hint has %1% templated %2%!!", "yellow" , "values")));
+
+    // NixLangError is just the same as NixLangWarning, except for the Error
+    // flag.
+    printErrorInfo(NixLangError()
+                   .name("error name")
+                   .description("error description")
+                   .pos(Pos(problem_symbol, 40, 13))
+                   .linesOfCode(std::optional("previous line of code"),
+                                "this is the problem line of code",
+                                std::optional("next line of code"))
+                   .hint(hintfmt("this hint has %1% templated %2%!!", "yellow", "values")));
+
+    return 0;
+}
diff --git a/src/error-demo/local.mk b/src/error-demo/local.mk
new file mode 100644
index 000000000..121cab9e3
--- /dev/null
+++ b/src/error-demo/local.mk
@@ -0,0 +1,10 @@
+programs += error-demo
+
+error-demo_DIR := $(d)
+
+error-demo_SOURCES := \
+  $(wildcard $(d)/*.cc) \
+
+error-demo_LIBS = libutil
+
+error-demo_LDFLAGS = -pthread $(SODIUM_LIBS) $(EDITLINE_LIBS) $(BOOST_LDFLAGS) -lboost_context -lboost_thread -lboost_system