Initial implementation of tuple demonstration

This allows allocating a buffer of double pointers pointing to
the memory location in a bunch of variables. It is not particularly
ergonomic as is, and it seems unlikely the real world performance
benefit will exist.

.github/workflows/busted.yml

@@ -1,3 +1,4 @@
+---
 name: Busted
 
 on: [push, pull_request]
@@ -35,19 +36,46 @@ jobs:
       - name: Setup dependencies
         run: |
           luarocks install busted
-          luarocks install luacov-coveralls
+          luarocks install luacov-reporter-lcov
-      - name: Build C library
+      - name: Build C++ library
         run: |
-          ${{ matrix.os == 'ubuntu-latest' && 'FSANITIZE=1' || '' }} luarocks make --no-install
+          luarocks make --no-install
+        env:
+          LJKIWI_LUA: ${{ startsWith(matrix.lua_version, 'luajit-') && '0' || '1' }}
+          LJKIWI_CFFI: ${{ startsWith(matrix.lua_version, 'luajit-') && '1' || '0' }}
+          FCOV: ${{ startsWith(matrix.os, 'ubuntu-') && '1' || '' }}
+          # Can't assume so versions, have to update this manually below
+          FSANITIZE: ${{ matrix.os == 'ubuntu-latest' && '1' || '' }}
+
       - name: Run busted tests
         run: |
-          ${{ matrix.os == 'ubuntu-latest' && 'LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libasan.so.6:/usr/lib/x86_64-linux-gnu/libstdc++.so.6:/usr/lib/x86_64-linux-gnu/libubsan.so.1' || '' }} busted -c -v
+          busted -c -v
-      - name: Report test coverage
-        if: success() && !startsWith(matrix.os, 'windows-') && startsWith(matrix.lua_version, 'luajit-')
-        continue-on-error: true
-        run: luacov-coveralls -e .luarocks -e spec
         env:
-          COVERALLS_REPO_TOKEN: ${{ github.token }}
+          LD_PRELOAD: |-
+            ${{ matrix.os == 'ubuntu-latest' &&
+            '/usr/lib/x86_64-linux-gnu/libasan.so.6:/usr/lib/x86_64-linux-gnu/libstdc++.so.6:/usr/lib/x86_64-linux-gnu/libubsan.so.1'
+            || '' }}
+
+      - name: Run gcov
+        if: success() && startsWith(matrix.os, 'ubuntu-')
+        run: |
+          gcov -p -b -s"$(pwd)" -r *.gcda
+          rm -f 'kiwi#'*.gcov
+
+      - name: generate Lua lcov test reports
+        if: |-
+          success() && !startsWith(matrix.os, 'windows-')
+          && startsWith(matrix.lua_version, 'luajit-')
+        run: luacov
+
+      - name: Report test coverage
+        if: |-
+          success() && !startsWith(matrix.os, 'windows-')
+          && (startsWith(matrix.lua_version, 'luajit-') || startsWith(matrix.os, 'ubuntu-'))
+        continue-on-error: true
+        uses: coverallsapp/github-action@v2
+        with:
+          flag-name: run ${{ join(matrix.*, ' - ') }}
 
   finish:
     if: always()
@@ -58,3 +86,25 @@ jobs:
         uses: coverallsapp/github-action@v2
         with:
           parallel-finished: true
+
+  publish:
+    if: github.ref_type == 'tag' && startsWith(github.ref_name, 'v')
+    needs: busted
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup ‘lua’
+        uses: jkl1337/gh-actions-lua@master
+        with:
+          luaVersion: "5.4.6"
+      - name: Setup ‘luarocks’
+        uses: jkl1337/gh-actions-luarocks@master
+      - name: Build C++ library
+        run: |
+          luarocks make --no-install
+      - name: Build rock
+        run: |
+          luarocks install dkjson
+          luarocks upload --api-key ${{ secrets.LUAROCKS_API_KEY }} \
+            rockspecs/kiwi-${GITHUB_REF_NAME#v}-1.rockspec

.gitignore

@@ -3,6 +3,11 @@
 /lua_modules
 /.luarocks
 /config.mk
+*.gcda
+*.gcno
+*.gcov
+*.lcov
+*.out
 *.pch
 *.gch
 *.lib
@@ -11,5 +16,6 @@
 *.obj
 *.exp
 *.dll
+*.rock
 .cache/
 compile_commands.json

.luacov

@@ -0,0 +1,5 @@
+modules = {
+   kiwi = "kiwi.lua",
+}
+reporter = "lcov"
+reportfile = "luacov.lcov"

Makefile

@@ -5,36 +5,57 @@ LIBFLAG := -shared
 LIB_EXT := $(if $(filter Windows_NT,$(OS)),dll,so)
 LUA_INCDIR := /usr/include
 
-SRCDIR := $(dir $(realpath $(lastword $(MAKEFILE_LIST))))
+SRCDIR := .
+
+SANITIZE_FLAGS := -fsanitize=undefined -fsanitize=address -fsanitize=alignment \
+  -fsanitize=shift -fsanitize=unreachable -fsanitize=bool -fsanitize=enum
+
+ifdef FDEBUG
+  OPTFLAG := -O2
+else
+  OPTFLAG := -Og -g
+endif
+
+COVERAGE_FLAGS := --coverage
+LTO_FLAGS := -flto=auto
 
 ifeq ($(OS),Windows_NT)
   is_clang = $(filter %clang++,$(CXX))
   is_gcc = $(filter %g++,$(CXX))
+
+  ifdef FSANITIZE
+    $(error "FSANITIZE is not supported on Windows")
+  endif
 else
   uname_s := $(shell uname -s)
   ifeq ($(uname_s),Darwin)
+    is_clang = 1
+    is_gcc =
+
     CC := env MACOSX_DEPLOYMENT_TARGET=11.0 gcc
     CXX := env MACOSX_DEPLOYMENT_TARGET=11.0 g++
     LIBFLAG := -bundle -undefined dynamic_lookup
-    is_clang = 1
+
-    is_gcc =
   else
     is_clang = $(filter %clang++,$(CXX))
     is_gcc = $(filter %g++,$(CXX))
+
+    SANITIZE_FLAGS += -fsanitize=bounds-strict
   endif
 endif
 
-OPTFLAG := -O2
-SANITIZE_FLAGS := -fsanitize=undefined -fsanitize=address -fsanitize=alignment -fsanitize=bounds-strict \
- -fsanitize=shift -fsanitize=unreachable -fsanitize=bool \
- -fsanitize=enum
-
-LTO_FLAGS := -flto=auto
-
 -include config.mk
 
 ifeq ($(origin LUAROCKS), command line)
-  CCFLAGS := $(CFLAGS)
+  ifdef FCOV
+    CCFLAGS := $(patsubst -O%,,$(CFLAGS))
+  else
+    ifdef FDEBUG
+      CCFLAGS := $(patsubst -O%,,$(CFLAGS)) -Og -g
+    else
+      CCFLAGS := $(CFLAGS)
+    endif
+  endif
   override CFLAGS := -std=c99 $(CCFLAGS)
 
   ifneq ($(filter %gcc,$(CC)),)
@@ -52,10 +73,13 @@ endif
 
 CCFLAGS += -Wall -fvisibility=hidden -Wformat=2 -Wconversion -Wimplicit-fallthrough
 
+ifdef FCOV
+  CCFLAGS += $(COVERAGE_FLAGS)
+endif
 ifdef FSANITIZE
   CCFLAGS += $(SANITIZE_FLAGS)
 endif
-ifndef FNOLTO
+ifdef FLTO
   CCFLAGS += $(LTO_FLAGS)
 endif
 
@@ -69,7 +93,7 @@ else
 endif
 
 override CPPFLAGS += -I$(SRCDIR) -I$(SRCDIR)/kiwi -I"$(LUA_INCDIR)"
-override CXXFLAGS += -std=c++14 -fno-rtti $(CCFLAGS)
+override CXXFLAGS += -std=c++17 -fno-rtti $(CCFLAGS)
 
 ifeq ($(OS),Windows_NT)
   override CPPFLAGS += -DLUA_BUILD_AS_DLL
@@ -80,11 +104,9 @@ ifdef LUA
   LUA_VERSION ?= $(lastword $(shell "$(LUA)" -e "print(_VERSION)"))
 endif
 
-ifndef LUA_VERSION
+ifdef LUA_VERSION
-  LJKIWI_CKIWI := 1
+ifneq ($(LUA_VERSION),5.1)
-else
+  LJKIWI_CFFI ?= 0
-ifeq ($(LUA_VERSION),5.1)
-  LJKIWI_CKIWI := 1
 endif
 endif
 
@@ -92,8 +114,10 @@ kiwi_lib_srcs := AssocVector.h constraint.h debug.h errors.h expression.h kiwi.h
   row.h shareddata.h solver.h solverimpl.h strength.h symbol.h symbolics.h term.h \
   util.h variable.h version.h
 
-objs := luakiwi.o
+ifneq ($(LJKIWI_LUA),0)
-ifdef LJKIWI_CKIWI
+  objs += luakiwi.o
+endif
+ifneq ($(LJKIWI_CFFI),0)
   objs += ckiwi.o
 endif
 
@@ -107,7 +131,7 @@ install:
 	$(CP) -f kiwi.lua $(INST_LUADIR)/kiwi.lua
 
 mostlyclean:
-	$(RM) -f ljkiwi.$(LIB_EXT) $(objs)
+	$(RM) -f ljkiwi.$(LIB_EXT) $(objs) $(objs:.o=.gcda) $(objs:.o=.gcno)
 
 clean: mostlyclean
 	$(RM) -f $(PCH)

README.md

@@ -9,13 +9,12 @@ ljkiwi - Free LuaJIT FFI and Lua C API kiwi (Cassowary derived) constraint solve
 Kiwi is a reasonably efficient C++ implementation of the Cassowary constraint solving algorithm. It is an implementation of the algorithm as described in the paper ["The Cassowary Linear Arithmetic Constraint Solving Algorithm"](http://www.cs.washington.edu/research/constraints/cassowary/techreports/cassowaryTR.pdf) by Greg J. Badros and Alan Borning. The Kiwi implementation is not based on the original C++ implementation, but is a ground-up reimplementation with performance 10x to 500x faster in typical use.
 Cassowary constraint solving is a technique that is particularly well suited to user interface layout. It is the algorithm Apple uses for iOS and OS X Auto Layout.
 
-There are a few Lua implementations or attempts. The SILE typesetting system has a pure Lua implementation of the original Cassowary code, which appears to be correct but is quite slow. There are two extant Lua ports of Kiwi, one that is based on a C rewrite of Kiwi. However testing of these was not encouraging with either segfaults or incorrect results.
+There are a few Lua implementations or attempts. The SILE typesetting system has a pure Lua implementation of the original Cassowary code, which appears to be correct but is quite slow. There are two extant Lua ports of Kiwi, one that is based on a C rewrite of Kiwi. However testing of these was not encouraging and they appear mostly unmaintained.
-Since the C++ Kiwi library is well tested and widely used it was simpler to provide a LuaJIT FFI wrapper. There is also a Lua C API binding with support for 5.1 through 5.4.
+Since the C++ Kiwi library is well tested, it was simpler to provide a LuaJIT FFI wrapper. Now, there is also a Lua C API binding with support for 5.1 through 5.4, and since
+in most common use cases all the heavy lifting is done in the library, there is usually
+no practical perfomance difference between the two.
 This package has no dependencies other than a supported C++14 compiler to compile the included Kiwi library and a small C wrapper.
 
-The Lua API has a pure Lua expression builder. There is of course some overhead to this, however in most cases expression building is infrequent and the underlying structures can be reused.
-
-The wrapper is quite close to the Kiwi C++/Python port with a few naming changes.
 
 ## Example
 
@@ -91,4 +90,4 @@ print(right_edge:value()) -- 500
 In addition to the expression builder there is a convenience constraints submodule with: `pair_ratio`, `pair`, and `single` to allow efficient construction of the most common simple expression types for GUI layout.
 
 ## Documentation
-WIP - However the API is fully annotated and will work with lua-language-server. Documentation can also be generated with lua-language-server.
+The API is fully annotated and will work with lua-language-server. Documentation can also be generated with lua-language-server.

ckiwi/ckiwi.cpp

@@ -3,6 +3,7 @@
 #include <kiwi/kiwi.h>
 
 #include <climits>
+#include <cstdarg>
 #include <cstdlib>
 #include <cstring>
 #include <string>
@@ -326,7 +327,7 @@ bool kiwi_solver_has_constraint(const KiwiSolver* s, KiwiConstraint* constraint)
 }
 
 const KiwiErr* kiwi_solver_add_edit_var(KiwiSolver* s, KiwiVar* var, double strength) {
-   return wrap_err(s, var, [strength](auto& s, auto&& v) {
+   return wrap_err(s, var, [strength](auto&& s, auto&& v) {
       s.addEditVariable(Variable(v), strength);
    });
 }
@@ -373,4 +374,31 @@ char* kiwi_solver_dumps(const KiwiSolver* s) {
    return buf;
 }
 
+void kiwi_tuple_init(KiwiTuple* tuple, int count, ...) {
+   if (lk_unlikely(!tuple))
+      return;
+
+   va_list args;
+   va_start(args, count);
+   for (int i = 0; i < count; ++i) {
+      auto* var = va_arg(args, KiwiVar*);
+      retain_unmanaged(var);
+      tuple->values[i] = &var->m_value;
+   }
+   tuple->count = count;
+   va_end(args);
+}
+
+void kiwi_tuple_destroy(KiwiTuple* tuple) {
+   if (lk_unlikely(!tuple))
+      return;
+
+   for (int i = 0; i < tuple->count; ++i) {
+      auto* value = const_cast<double*>(tuple->values[i]);
+      release_unmanaged(
+          reinterpret_cast<KiwiVar*>(reinterpret_cast<char*>(value) - offsetof(KiwiVar, m_value))
+      );
+   }
+}
+
 }  // extern "C"

ckiwi/ckiwi.h

@@ -61,7 +61,7 @@ typedef struct KiwiExpression {
 #if defined(LJKIWI_LUAJIT_DEF)
    KiwiTerm terms_[?];
 #elif defined(LJKIWI_USE_FAM_1)
-   KiwiTerm terms_[1];  // LuaJIT: struct KiwiTerm terms_[?];
+   KiwiTerm terms_[1];
 #else
    KiwiTerm terms_[];
 #endif
@@ -74,8 +74,22 @@ typedef struct KiwiErr {
    bool must_free;
 } KiwiErr;
 
+typedef struct KiwiTuple {
+   int count;
+#if defined(LJKIWI_LUAJIT_DEF)
+   const double* values[?];
+#elif defined(LJKIWI_USE_FAM_1)
+   const double* values[1];
+#else
+   const double* values[];
+#endif
+} KiwiTuple;
+
 struct KiwiSolver;
 
+LJKIWI_EXP void kiwi_tuple_init(KiwiTuple* tuple, int count, ...);
+LJKIWI_EXP void kiwi_tuple_destroy(KiwiTuple* tuple);
+
 LJKIWI_EXP KiwiVar* kiwi_var_construct(const char* name);
 LJKIWI_EXP void kiwi_var_release(KiwiVar* var);
 LJKIWI_EXP void kiwi_var_retain(KiwiVar* var);

kiwi.lua

@@ -64,8 +64,16 @@ typedef struct KiwiErr {
    bool must_free;
 } KiwiErr;
 
+typedef struct KiwiTuple {
+   int count;
+   const double* values[?];
+} KiwiTuple;
+
 struct KiwiSolver;
 
+void kiwi_tuple_init(KiwiTuple* tuple, int count, ...);
+void kiwi_tuple_destroy(KiwiTuple* tuple);
+
 KiwiVar* kiwi_var_construct(const char* name);
 void kiwi_var_release(KiwiVar* var);
 void kiwi_var_retain(KiwiVar* var);
@@ -175,6 +183,7 @@ function kiwi.is_var(o)
 end
 
 local Term = ffi.typeof("struct KiwiTerm") --[[@as kiwi.Term]]
+local SIZEOF_TERM = assert(ffi.sizeof(Term))
 kiwi.Term = Term
 
 function kiwi.is_term(o)
@@ -195,18 +204,28 @@ function kiwi.is_constraint(o)
    return ffi_istype(Constraint, o)
 end
 
+local Tuple = ffi.typeof("struct KiwiTuple") --[[@as kiwi.Tuple]]
+kiwi.Tuple = Tuple
+
+---@class kiwi.Tuple: ffi.cdata*
+---@field values ffi.cdata*
+---@field count integer
+---@overload fun(vars: kiwi.Var[]): kiwi.Tuple
+ffi.metatype(Tuple, {
+   __new = function(self, vars)
+      local t = ffi_new(self, #vars)
+      ljkiwi.kiwi_tuple_init(t, #vars, unpack(vars))
+      return ffi_gc(t, ljkiwi.kiwi_tuple_destroy)
+   end,
+})
+
 ---@param expr kiwi.Expression
 ---@param var kiwi.Var
 ---@param coeff number?
 ---@nodiscard
 local function add_expr_term(expr, var, coeff)
    local ret = ffi_gc(ffi_new(Expression, expr.term_count + 1), ljkiwi.kiwi_expression_destroy) --[[@as kiwi.Expression]]
-   for i = 0, expr.term_count - 1 do
+   ffi_copy(ret.terms_, expr.terms_, SIZEOF_TERM * expr.term_count)
-      local st = expr.terms_[i] --[[@as kiwi.Term]]
-      local dt = ret.terms_[i] --[[@as kiwi.Term]]
-      dt.var = st.var
-      dt.coefficient = st.coefficient
-   end
    local dt = ret.terms_[expr.term_count]
    dt.var = var
    dt.coefficient = coeff or 1.0
@@ -282,8 +301,6 @@ local OP_NAMES = {
    EQ = "==",
 }
 
-local SIZEOF_TERM = ffi.sizeof(Term) --[[@as integer]]
-
 local tmpexpr = ffi_new(Expression, 2) --[[@as kiwi.Expression]]
 local tmpexpr_r = ffi_new(Expression, 1) --[[@as kiwi.Expression]]
 
@@ -622,13 +639,7 @@ do
    ---@nodiscard
    local function new_expr_constant(expr, constant)
       local ret = ffi_gc(ffi_new(Expression, expr.term_count), ljkiwi.kiwi_expression_destroy) --[[@as kiwi.Expression]]
-
+      ffi_copy(ret.terms_, expr.terms_, SIZEOF_TERM * expr.term_count)
-      for i = 0, expr.term_count - 1 do
-         local dt = ret.terms_[i] --[[@as kiwi.Term]]
-         local st = expr.terms_[i] --[[@as kiwi.Term]]
-         dt.var = st.var
-         dt.coefficient = st.coefficient
-      end
       ret.constant = constant
       ret.term_count = expr.term_count
       ljkiwi.kiwi_expression_retain(ret)

kiwi/kiwi/variable.h

@@ -33,7 +33,6 @@ public:
     double value() const { return m_value; }
     void setValue(double value) { m_value = value; }
 
-private:
     std::string m_name;
     double m_value;
 

luakiwi/luakiwi.cpp

@@ -248,6 +248,7 @@ KiwiTerm* term_new(lua_State* L) {
 
 inline KiwiExpression* expr_new(lua_State* L, int nterms) {
    auto* expr = static_cast<KiwiExpression*>(lua_newuserdata(L, KiwiExpression::sz(nterms)));
+   expr->term_count = 0;
    expr->owner = nullptr;
    push_type(L, EXPR);
    lua_setmetatable(L, -2);
@@ -265,7 +266,8 @@ inline ConstraintData* constraint_new(
    push_type(L, CONSTRAINT);
    lua_setmetatable(L, -2);
 
-   if (lk_unlikely(!(*c = kiwi_constraint_new(lhs, rhs, op, strength)))) {
+   *c = kiwi_constraint_new(lhs, rhs, op, strength);
+   if (lk_unlikely(!*c)) {
       lua_rawgeti(L, lua_upvalueindex(1), MEM_ERR_MSG);
       lua_error(L);
    }
@@ -929,9 +931,8 @@ int lkiwi_expr_new(lua_State* L) {
 
    auto* expr = expr_new(L, nterms);
    expr->constant = constant;
-   expr->term_count = nterms;
 
-   for (int i = 0; i < nterms; i++) {
+   for (int i = 0; i < nterms; ++i, ++expr->term_count) {
       const auto* term = get_term(L, i + 2);
       expr->terms[i].var = retain_unmanaged(term->var);
       expr->terms[i].coefficient = term->coefficient;

rockspecs/kiwi-0.1.1-1.rockspec

@@ -0,0 +1,40 @@
+rockspec_format = "3.0"
+package = "kiwi"
+version = "0.1.1-1"
+source = {
+   url = "git+https://github.com/jkl1337/ljkiwi",
+   tag = "v0.1.1",
+}
+description = {
+   summary = "LuaJIT FFI and Lua binding for the Kiwi constraint solver.",
+   detailed = [[
+      kiwi is a LuaJIT FFI and Lua binding for the Kiwi constraint solver. Kiwi is a fast
+      implementation of the Cassowary constraint solving algorithm. kiwi provides
+      reasonably efficient bindings using the LuaJIT FFI and convential Lua C bindings.]],
+   license = "MIT",
+   issues_url = "https://github.com/jkl1337/ljkiwi/issues",
+   maintainer = "John Luebs",
+}
+dependencies = {
+   "lua >= 5.1",
+}
+
+build = {
+   type = "make",
+   build_variables = {
+      LUAROCKS = "1",
+      LUA = "$(LUA)",
+      CFLAGS = "$(CFLAGS)",
+      LUA_INCDIR = "$(LUA_INCDIR)",
+      LUA_LIBDIR = "$(LUA_LIBDIR)",
+      LUALIB = "$(LUALIB)",
+      LIBFLAG = "$(LIBFLAG)",
+      LIB_EXT = "$(LIB_EXTENSION)",
+      OBJ_EXT = "$(OBJ_EXTENSION)",
+   },
+   install_variables = {
+      INST_LIBDIR = "$(LIBDIR)",
+      INST_LUADIR = "$(LUADIR)",
+      LIB_EXT = "$(LIB_EXTENSION)",
+   },
+}

spec/expression_spec.lua

@@ -0,0 +1,240 @@
+expose("module", function()
+   require("kiwi")
+end)
+
+describe("Expression", function()
+   local kiwi = require("kiwi")
+   local LUA_VERSION = tonumber(_VERSION:match("%d+%.%d+"))
+
+   it("construction", function()
+      local v = kiwi.Var("foo")
+      local v2 = kiwi.Var("bar")
+      local v3 = kiwi.Var("aux")
+      local e1 = kiwi.Expression(0, v * 1, v2 * 2, v3 * 3)
+      local e2 = kiwi.Expression(10, v * 1, v2 * 2, v3 * 3)
+
+      local constants = { 0, 10 }
+      for i, e in ipairs({ e1, e2 }) do
+         assert.equal(constants[i], e.constant)
+         local terms = e:terms()
+         assert.equal(3, #terms)
+         assert.equal(v, terms[1].var)
+         assert.equal(1.0, terms[1].coefficient)
+         assert.equal(v2, terms[2].var)
+         assert.equal(2.0, terms[2].coefficient)
+         assert.equal(v3, terms[3].var)
+         assert.equal(3.0, terms[3].coefficient)
+      end
+
+      if LUA_VERSION <= 5.2 then
+         assert.equal("1 foo + 2 bar + 3 aux + 10", tostring(e2))
+      else
+         assert.equal("1.0 foo + 2.0 bar + 3.0 aux + 10.0", tostring(e2))
+      end
+
+      assert.error(function()
+         kiwi.Expression(0, 0, v2 * 2, v3 * 3)
+      end)
+   end)
+
+   describe("method", function()
+      local v, t, e
+      before_each(function()
+         v = kiwi.Var("foo")
+         v:set(42)
+         t = kiwi.Term(v, 10)
+         e = t + 5
+      end)
+
+      it("has value", function()
+         v:set(42)
+         assert.equal(425, e:value())
+         v:set(87)
+         assert.equal(875, e:value())
+      end)
+
+      it("can be copied", function()
+         local e2 = e:copy()
+         assert.equal(e.constant, e2.constant)
+         local t1, t2 = e:terms(), e2:terms()
+         assert.equal(#t1, #t2)
+         for i = 1, #t1 do
+            assert.equal(t1[i].var, t2[i].var)
+            assert.equal(t1[i].coefficient, t2[i].coefficient)
+         end
+      end)
+
+      it("neg", function()
+         local neg = -e --[[@as kiwi.Expression]]
+         assert.True(kiwi.is_expression(neg))
+         local terms = neg:terms()
+         assert.equal(1, #terms)
+         assert.equal(v, terms[1].var)
+         assert.equal(-10.0, terms[1].coefficient)
+         assert.equal(-5, neg.constant)
+      end)
+
+      describe("bin op", function()
+         local v2, t2, e2
+         before_each(function()
+            v2 = kiwi.Var("bar")
+            t2 = kiwi.Term(v2)
+            e2 = v2 - 10
+         end)
+
+         it("mul", function()
+            for _, prod in ipairs({ e * 2.0, 2 * e }) do
+               assert.True(kiwi.is_expression(prod))
+               local terms = prod:terms()
+               assert.equal(1, #terms)
+               assert.equal(v, terms[1].var)
+               assert.equal(20.0, terms[1].coefficient)
+               assert.equal(10, prod.constant)
+            end
+
+            assert.error(function()
+               local _ = e * v
+            end)
+         end)
+
+         it("div", function()
+            local quot = e / 2.0
+            assert.True(kiwi.is_expression(quot))
+            local terms = quot:terms()
+            assert.equal(1, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(5.0, terms[1].coefficient)
+            assert.equal(2.5, quot.constant)
+
+            assert.error(function()
+               local _ = e / v2
+            end)
+         end)
+
+         it("add", function()
+            for _, sum in ipairs({ e + 2.0, 2 + e }) do
+               assert.True(kiwi.is_expression(sum))
+               assert.equal(7.0, sum.constant)
+
+               local terms = sum:terms()
+               assert.equal(1, #terms)
+               assert.equal(10.0, terms[1].coefficient)
+               assert.equal(v, terms[1].var)
+            end
+
+            local sum = e + v2
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(5, sum.constant)
+            local terms = sum:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+
+            sum = e + t2
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(5, sum.constant)
+            terms = sum:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+
+            sum = e + e2
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(-5, sum.constant)
+            terms = sum:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+
+            assert.error(function()
+               local _ = t + "foo"
+            end)
+            assert.error(function()
+               local _ = t + {}
+            end)
+         end)
+
+         it("sub", function()
+            local constants = { 3, -3 }
+            for i, diff in ipairs({ e - 2.0, 2 - e }) do
+               local constant = constants[i]
+               assert.True(kiwi.is_expression(diff))
+               assert.equal(constant, diff.constant)
+
+               local terms = diff:terms()
+               assert.equal(1, #terms)
+               assert.equal(v, terms[1].var)
+               assert.equal(constant < 0 and -10.0 or 10.0, terms[1].coefficient)
+            end
+
+            local diff = e - v2
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(5, diff.constant)
+            local terms = diff:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(-1.0, terms[2].coefficient)
+
+            diff = e - t2
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(5, diff.constant)
+            terms = diff:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(-1.0, terms[2].coefficient)
+
+            diff = e - e2
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(15, diff.constant)
+            terms = diff:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(-1.0, terms[2].coefficient)
+
+            assert.error(function()
+               local _ = e - "foo"
+            end)
+            assert.error(function()
+               local _ = e - {}
+            end)
+         end)
+
+         it("constraint expr op expr", function()
+            local ops = { "LE", "EQ", "GE" }
+            for i, meth in ipairs({ "le", "eq", "ge" }) do
+               local c = e[meth](e, e2)
+               assert.True(kiwi.is_constraint(c))
+
+               local expr = c:expression()
+               local terms = expr:terms()
+               assert.equal(2, #terms)
+
+               -- order can be randomized due to use of map
+               if terms[1].var ~= v then
+                  terms[1], terms[2] = terms[2], terms[1]
+               end
+               assert.equal(v, terms[1].var)
+               assert.equal(10.0, terms[1].coefficient)
+               assert.equal(v2, terms[2].var)
+               assert.equal(-1.0, terms[2].coefficient)
+
+               assert.equal(15, expr.constant)
+               assert.equal(ops[i], c:op())
+               assert.equal(kiwi.strength.REQUIRED, c:strength())
+            end
+         end)
+      end)
+   end)
+end)

spec/term_spec.lua

@@ -0,0 +1,245 @@
+expose("module", function()
+   require("kiwi")
+end)
+
+describe("Term", function()
+   local kiwi = require("kiwi")
+   local LUA_VERSION = tonumber(_VERSION:match("%d+%.%d+"))
+
+   it("construction", function()
+      local v = kiwi.Var("foo")
+      local t = kiwi.Term(v)
+      assert.equal(v, t.var)
+      assert.equal(1.0, t.coefficient)
+
+      t = kiwi.Term(v, 100)
+      assert.equal(v, t.var)
+      assert.equal(100, t.coefficient)
+
+      if LUA_VERSION <= 5.2 then
+         assert.equal("100 foo", tostring(t))
+      else
+         assert.equal("100.0 foo", tostring(t))
+      end
+
+      assert.error(function()
+         kiwi.Term("")
+      end)
+   end)
+
+   describe("method", function()
+      local v, v2, t, t2
+
+      before_each(function()
+         v = kiwi.Var("foo")
+         t = kiwi.Term(v, 10)
+      end)
+
+      it("has value", function()
+         v:set(42)
+         assert.equal(420, t:value())
+         v:set(87)
+         assert.equal(870, t:value())
+      end)
+
+      it("has toexpr", function()
+         local e = t:toexpr()
+         assert.True(kiwi.is_expression(e))
+         assert.equal(0, e.constant)
+         local terms = e:terms()
+         assert.equal(1, #terms)
+         assert.equal(v, terms[1].var)
+         assert.equal(10.0, terms[1].coefficient)
+      end)
+
+      it("neg", function()
+         local neg = -t --[[@as kiwi.Term]]
+         assert.True(kiwi.is_term(neg))
+         assert.equal(v, neg.var)
+         assert.equal(-10, neg.coefficient)
+      end)
+
+      describe("bin op", function()
+         before_each(function()
+            v2 = kiwi.Var("bar")
+            t2 = kiwi.Term(v2)
+         end)
+
+         it("mul", function()
+            for _, prod in ipairs({ t * 2.0, 2 * t }) do
+               assert.True(kiwi.is_term(prod))
+               assert.equal(v, prod.var)
+               assert.equal(20, prod.coefficient)
+            end
+
+            assert.error(function()
+               local _ = t * v
+            end)
+         end)
+
+         it("div", function()
+            local quot = t / 2.0
+            assert.True(kiwi.is_term(quot))
+            assert.equal(v, quot.var)
+            assert.equal(5.0, quot.coefficient)
+
+            assert.error(function()
+               local _ = v / v2
+            end)
+         end)
+
+         it("add", function()
+            for _, sum in ipairs({ t + 2.0, 2 + t }) do
+               assert.True(kiwi.is_expression(sum))
+               assert.equal(2.0, sum.constant)
+
+               local terms = sum:terms()
+               assert.equal(1, #terms)
+               assert.equal(10.0, terms[1].coefficient)
+               assert.equal(v, terms[1].var)
+            end
+
+            local sum = t + v2
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(0, sum.constant)
+            local terms = sum:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+
+            sum = t + t2
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(0, sum.constant)
+            terms = sum:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+
+            local t3 = kiwi.Term(v2, 20)
+            sum = t3 + sum
+            assert.True(kiwi.is_expression(sum))
+            assert.equal(0, sum.constant)
+            terms = sum:terms()
+            assert.equal(3, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+            assert.equal(v2, terms[3].var)
+            assert.equal(20.0, terms[3].coefficient)
+
+            assert.error(function()
+               local _ = t + "foo"
+            end)
+            assert.error(function()
+               local _ = t + {}
+            end)
+         end)
+
+         it("sub", function()
+            local constants = { -2, 2 }
+            for i, diff in ipairs({ t - 2.0, 2 - t }) do
+               local constant = constants[i]
+               assert.True(kiwi.is_expression(diff))
+               assert.equal(constant, diff.constant)
+
+               local terms = diff:terms()
+               assert.equal(1, #terms)
+               assert.equal(v, terms[1].var)
+               assert.equal(constant < 0 and 10.0 or -10.0, terms[1].coefficient)
+            end
+
+            local diff = t - v2
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(0, diff.constant)
+            local terms = diff:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(-1.0, terms[2].coefficient)
+
+            diff = t - t2
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(0, diff.constant)
+            terms = diff:terms()
+            assert.equal(2, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(-1.0, terms[2].coefficient)
+
+            local t3 = kiwi.Term(v2, 20)
+            diff = t3 - diff
+            assert.True(kiwi.is_expression(diff))
+            assert.equal(0, diff.constant)
+            terms = diff:terms()
+            assert.equal(3, #terms)
+            assert.equal(v, terms[1].var)
+            assert.equal(-10.0, terms[1].coefficient)
+            assert.equal(v2, terms[2].var)
+            assert.equal(1.0, terms[2].coefficient)
+            assert.equal(v2, terms[3].var)
+            assert.equal(20.0, terms[3].coefficient)
+
+            assert.error(function()
+               local _ = t - "foo"
+            end)
+            assert.error(function()
+               local _ = t - {}
+            end)
+         end)
+
+         it("constraint term op expr", function()
+            local ops = { "LE", "EQ", "GE" }
+            for i, meth in ipairs({ "le", "eq", "ge" }) do
+               local c = t[meth](t, v2 + 1)
+               assert.True(kiwi.is_constraint(c))
+
+               local e = c:expression()
+               local terms = e:terms()
+               assert.equal(2, #terms)
+
+               -- order can be randomized due to use of map
+               if terms[1].var ~= v then
+                  terms[1], terms[2] = terms[2], terms[1]
+               end
+               assert.equal(v, terms[1].var)
+               assert.equal(10.0, terms[1].coefficient)
+               assert.equal(v2, terms[2].var)
+               assert.equal(-1.0, terms[2].coefficient)
+
+               assert.equal(-1, e.constant)
+               assert.equal(ops[i], c:op())
+               assert.equal(kiwi.strength.REQUIRED, c:strength())
+            end
+         end)
+
+         it("constraint term op term", function()
+            for i, meth in ipairs({ "le", "eq", "ge" }) do
+               local c = t[meth](t, t2)
+               assert.True(kiwi.is_constraint(c))
+
+               local e = c:expression()
+               local terms = e:terms()
+               assert.equal(2, #terms)
+
+               -- order can be randomized due to use of map
+               if terms[1].var ~= v then
+                  terms[1], terms[2] = terms[2], terms[1]
+               end
+               assert.equal(v, terms[1].var)
+               assert.equal(10.0, terms[1].coefficient)
+               assert.equal(v2, terms[2].var)
+               assert.equal(-1.0, terms[2].coefficient)
+
+               assert.equal(0, e.constant)
+            end
+         end)
+      end)
+   end)
+end)

spec/var_spec.lua

@@ -127,6 +127,8 @@ describe("Var", function()
             assert.equal(v2, terms[2].var)
             assert.equal(-1.0, terms[2].coefficient)
 
+            -- TODO: terms and expressions
+
             assert.error(function()
                local _ = v - "foo"
             end)