Implement Expressions (#9439)

Ports https://github.com/mapbox/mapbox-gl-js/pull/4777 (and its several follow-ups)

97 files changed, 1012 insertions, 0 deletions

diff --git a/test/fixtures/expression_equality/acos.a.json b/test/fixtures/expression_equality/acos.a.json
new file mode 100644
index 0000000000..1e9bb752ca
--- /dev/null
+++ b/test/fixtures/expression_equality/acos.a.json
@@ -0,0 +1,4 @@
+[
+  "acos",
+  0.5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/acos.b.json b/test/fixtures/expression_equality/acos.b.json
new file mode 100644
index 0000000000..54e035cb7e
--- /dev/null
+++ b/test/fixtures/expression_equality/acos.b.json
@@ -0,0 +1,4 @@
+[
+  "acos",
+  1.5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/all.a.json b/test/fixtures/expression_equality/all.a.json
new file mode 100644
index 0000000000..ec7154b7b9
--- /dev/null
+++ b/test/fixtures/expression_equality/all.a.json
@@ -0,0 +1,17 @@
+[
+  "all",
+  [
+    "boolean",
+    [
+      "get",
+      "x"
+    ]
+  ],
+  [
+    "boolean",
+    [
+      "get",
+      "y"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/all.b.json b/test/fixtures/expression_equality/all.b.json
new file mode 100644
index 0000000000..8eab839bb0
--- /dev/null
+++ b/test/fixtures/expression_equality/all.b.json
@@ -0,0 +1,17 @@
+[
+  "all",
+  [
+    "boolean",
+    [
+      "get",
+      "x"
+    ]
+  ],
+  [
+    "boolean",
+    [
+      "get",
+      "y_other"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/any.a.json b/test/fixtures/expression_equality/any.a.json
new file mode 100644
index 0000000000..3f044c1f79
--- /dev/null
+++ b/test/fixtures/expression_equality/any.a.json
@@ -0,0 +1,17 @@
+[
+  "any",
+  [
+    "boolean",
+    [
+      "get",
+      "x"
+    ]
+  ],
+  [
+    "boolean",
+    [
+      "get",
+      "y"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/any.b.json b/test/fixtures/expression_equality/any.b.json
new file mode 100644
index 0000000000..720662751f
--- /dev/null
+++ b/test/fixtures/expression_equality/any.b.json
@@ -0,0 +1,17 @@
+[
+  "any",
+  [
+    "boolean",
+    [
+      "get",
+      "x"
+    ]
+  ],
+  [
+    "boolean",
+    [
+      "get",
+      "y_other"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/array.a.json b/test/fixtures/expression_equality/array.a.json
new file mode 100644
index 0000000000..3c31303ca3
--- /dev/null
+++ b/test/fixtures/expression_equality/array.a.json
@@ -0,0 +1,11 @@
+[
+  "array",
+  [
+    "literal",
+    [
+      1,
+      2,
+      3
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/array.b.json b/test/fixtures/expression_equality/array.b.json
new file mode 100644
index 0000000000..7606794d56
--- /dev/null
+++ b/test/fixtures/expression_equality/array.b.json
@@ -0,0 +1,11 @@
+[
+  "array",
+  [
+    "literal",
+    [
+      1,
+      2,
+      4
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/asin.a.json b/test/fixtures/expression_equality/asin.a.json
new file mode 100644
index 0000000000..3cd730ccbf
--- /dev/null
+++ b/test/fixtures/expression_equality/asin.a.json
@@ -0,0 +1,4 @@
+[
+  "asin",
+  0.5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/asin.b.json b/test/fixtures/expression_equality/asin.b.json
new file mode 100644
index 0000000000..2c862c8cbe
--- /dev/null
+++ b/test/fixtures/expression_equality/asin.b.json
@@ -0,0 +1,4 @@
+[
+  "asin",
+  1.5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/at.a.json b/test/fixtures/expression_equality/at.a.json
new file mode 100644
index 0000000000..c69b0d933b
--- /dev/null
+++ b/test/fixtures/expression_equality/at.a.json
@@ -0,0 +1,20 @@
+[
+  "number",
+  [
+    "at",
+    [
+      "number",
+      [
+        "get",
+        "i"
+      ]
+    ],
+    [
+      "array",
+      [
+        "get",
+        "arr"
+      ]
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/at.b.json b/test/fixtures/expression_equality/at.b.json
new file mode 100644
index 0000000000..6e19c28606
--- /dev/null
+++ b/test/fixtures/expression_equality/at.b.json
@@ -0,0 +1,20 @@
+[
+  "number",
+  [
+    "at",
+    [
+      "number",
+      [
+        "get",
+        "i"
+      ]
+    ],
+    [
+      "array",
+      [
+        "get",
+        "arr_other"
+      ]
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/atan.a.json b/test/fixtures/expression_equality/atan.a.json
new file mode 100644
index 0000000000..b76406bc44
--- /dev/null
+++ b/test/fixtures/expression_equality/atan.a.json
@@ -0,0 +1,4 @@
+[
+  "atan",
+  1
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/atan.b.json b/test/fixtures/expression_equality/atan.b.json
new file mode 100644
index 0000000000..aafbbb0594
--- /dev/null
+++ b/test/fixtures/expression_equality/atan.b.json
@@ -0,0 +1,4 @@
+[
+  "atan",
+  2
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/boolean.a.json b/test/fixtures/expression_equality/boolean.a.json
new file mode 100644
index 0000000000..1230a2a926
--- /dev/null
+++ b/test/fixtures/expression_equality/boolean.a.json
@@ -0,0 +1,7 @@
+[
+  "boolean",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/boolean.b.json b/test/fixtures/expression_equality/boolean.b.json
new file mode 100644
index 0000000000..1ae91ef60c
--- /dev/null
+++ b/test/fixtures/expression_equality/boolean.b.json
@@ -0,0 +1,7 @@
+[
+  "boolean",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/case.a.json b/test/fixtures/expression_equality/case.a.json
new file mode 100644
index 0000000000..84049294f5
--- /dev/null
+++ b/test/fixtures/expression_equality/case.a.json
@@ -0,0 +1,14 @@
+[
+  "case",
+  [
+    "get",
+    "x"
+  ],
+  "x",
+  [
+    "get",
+    "y"
+  ],
+  "y",
+  "otherwise"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/case.b.json b/test/fixtures/expression_equality/case.b.json
new file mode 100644
index 0000000000..038806043f
--- /dev/null
+++ b/test/fixtures/expression_equality/case.b.json
@@ -0,0 +1,14 @@
+[
+  "case",
+  [
+    "get",
+    "x"
+  ],
+  "x",
+  [
+    "get",
+    "y"
+  ],
+  "y",
+  "otherwise_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/coalesce.a.json b/test/fixtures/expression_equality/coalesce.a.json
new file mode 100644
index 0000000000..8fae579e7c
--- /dev/null
+++ b/test/fixtures/expression_equality/coalesce.a.json
@@ -0,0 +1,16 @@
+[
+  "coalesce",
+  [
+    "get",
+    "x"
+  ],
+  [
+    "get",
+    "y"
+  ],
+  [
+    "get",
+    "z"
+  ],
+  0
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/coalesce.b.json b/test/fixtures/expression_equality/coalesce.b.json
new file mode 100644
index 0000000000..4e0af8baa0
--- /dev/null
+++ b/test/fixtures/expression_equality/coalesce.b.json
@@ -0,0 +1,16 @@
+[
+  "coalesce",
+  [
+    "get",
+    "x"
+  ],
+  [
+    "get",
+    "y"
+  ],
+  [
+    "get",
+    "z"
+  ],
+  1
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/concat.a.json b/test/fixtures/expression_equality/concat.a.json
new file mode 100644
index 0000000000..08c95d7f49
--- /dev/null
+++ b/test/fixtures/expression_equality/concat.a.json
@@ -0,0 +1,6 @@
+[
+  "concat",
+  "a",
+  "b",
+  "c"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/concat.b.json b/test/fixtures/expression_equality/concat.b.json
new file mode 100644
index 0000000000..e3396d4fc0
--- /dev/null
+++ b/test/fixtures/expression_equality/concat.b.json
@@ -0,0 +1,6 @@
+[
+  "concat",
+  "a",
+  "b",
+  "c_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/cos.a.json b/test/fixtures/expression_equality/cos.a.json
new file mode 100644
index 0000000000..e41430de53
--- /dev/null
+++ b/test/fixtures/expression_equality/cos.a.json
@@ -0,0 +1,4 @@
+[
+  "cos",
+  0
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/cos.b.json b/test/fixtures/expression_equality/cos.b.json
new file mode 100644
index 0000000000..5ba4424dae
--- /dev/null
+++ b/test/fixtures/expression_equality/cos.b.json
@@ -0,0 +1,4 @@
+[
+  "cos",
+  1
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/divide.a.json b/test/fixtures/expression_equality/divide.a.json
new file mode 100644
index 0000000000..40a67a871c
--- /dev/null
+++ b/test/fixtures/expression_equality/divide.a.json
@@ -0,0 +1,5 @@
+[
+  "/",
+  10,
+  5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/divide.b.json b/test/fixtures/expression_equality/divide.b.json
new file mode 100644
index 0000000000..e3f7b155b2
--- /dev/null
+++ b/test/fixtures/expression_equality/divide.b.json
@@ -0,0 +1,5 @@
+[
+  "/",
+  10,
+  6
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/downcase.a.json b/test/fixtures/expression_equality/downcase.a.json
new file mode 100644
index 0000000000..ca367218c4
--- /dev/null
+++ b/test/fixtures/expression_equality/downcase.a.json
@@ -0,0 +1,4 @@
+[
+  "downcase",
+  "StRiNg"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/downcase.b.json b/test/fixtures/expression_equality/downcase.b.json
new file mode 100644
index 0000000000..fd9ea9881d
--- /dev/null
+++ b/test/fixtures/expression_equality/downcase.b.json
@@ -0,0 +1,4 @@
+[
+  "downcase",
+  "StRiNg_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/get.a.json b/test/fixtures/expression_equality/get.a.json
new file mode 100644
index 0000000000..57c3df48e7
--- /dev/null
+++ b/test/fixtures/expression_equality/get.a.json
@@ -0,0 +1,7 @@
+[
+  "number",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/get.b.json b/test/fixtures/expression_equality/get.b.json
new file mode 100644
index 0000000000..d1843362d3
--- /dev/null
+++ b/test/fixtures/expression_equality/get.b.json
@@ -0,0 +1,7 @@
+[
+  "number",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/has.a.json b/test/fixtures/expression_equality/has.a.json
new file mode 100644
index 0000000000..8326754107
--- /dev/null
+++ b/test/fixtures/expression_equality/has.a.json
@@ -0,0 +1,4 @@
+[
+  "has",
+  "x"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/has.b.json b/test/fixtures/expression_equality/has.b.json
new file mode 100644
index 0000000000..20b6072303
--- /dev/null
+++ b/test/fixtures/expression_equality/has.b.json
@@ -0,0 +1,4 @@
+[
+  "has",
+  "x_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/heatmap-density.a.json b/test/fixtures/expression_equality/heatmap-density.a.json
new file mode 100644
index 0000000000..90bd396f54
--- /dev/null
+++ b/test/fixtures/expression_equality/heatmap-density.a.json
@@ -0,0 +1,23 @@
+[
+  "interpolate",
+  [
+    "linear"
+  ],
+  [
+    "heatmap-density"
+  ],
+  0,
+  [
+    "rgb",
+    0,
+    0,
+    255
+  ],
+  1,
+  [
+    "rgb",
+    255,
+    0,
+    0
+  ]
+]
diff --git a/test/fixtures/expression_equality/heatmap-density.b.json b/test/fixtures/expression_equality/heatmap-density.b.json
new file mode 100644
index 0000000000..bce8ab03a1
--- /dev/null
+++ b/test/fixtures/expression_equality/heatmap-density.b.json
@@ -0,0 +1,23 @@
+[
+  "interpolate",
+  [
+    "linear"
+  ],
+  [
+    "heatmap-density"
+  ],
+  0,
+  [
+    "rgb",
+    0,
+    0,
+    255
+  ],
+  1,
+  [
+    "rgb",
+    255,
+    255,
+    255
+  ]
+]
diff --git a/test/fixtures/expression_equality/let.a.json b/test/fixtures/expression_equality/let.a.json
new file mode 100644
index 0000000000..fb24e50cfb
--- /dev/null
+++ b/test/fixtures/expression_equality/let.a.json
@@ -0,0 +1,25 @@
+[
+  "let",
+  "a",
+  1,
+  "b",
+  2,
+  [
+    "+",
+    [
+      "+",
+      [
+        "var",
+        "a"
+      ],
+      [
+        "var",
+        "b"
+      ]
+    ],
+    [
+      "var",
+      "a"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/let.b.json b/test/fixtures/expression_equality/let.b.json
new file mode 100644
index 0000000000..26813cb6ff
--- /dev/null
+++ b/test/fixtures/expression_equality/let.b.json
@@ -0,0 +1,25 @@
+[
+  "let",
+  "a",
+  1,
+  "b",
+  3,
+  [
+    "+",
+    [
+      "+",
+      [
+        "var",
+        "a"
+      ],
+      [
+        "var",
+        "b"
+      ]
+    ],
+    [
+      "var",
+      "b"
+    ]
+  ]
+]
diff --git a/test/fixtures/expression_equality/ln.a.json b/test/fixtures/expression_equality/ln.a.json
new file mode 100644
index 0000000000..30d80f36ae
--- /dev/null
+++ b/test/fixtures/expression_equality/ln.a.json
@@ -0,0 +1,4 @@
+[
+  "ln",
+  2
+]
diff --git a/test/fixtures/expression_equality/ln.b.json b/test/fixtures/expression_equality/ln.b.json
new file mode 100644
index 0000000000..9bc04ad586
--- /dev/null
+++ b/test/fixtures/expression_equality/ln.b.json
@@ -0,0 +1,6 @@
+[
+  "ln",
+  [
+    "e"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/log10.a.json b/test/fixtures/expression_equality/log10.a.json
new file mode 100644
index 0000000000..32e4c18807
--- /dev/null
+++ b/test/fixtures/expression_equality/log10.a.json
@@ -0,0 +1,4 @@
+[
+  "log10",
+  100
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/log10.b.json b/test/fixtures/expression_equality/log10.b.json
new file mode 100644
index 0000000000..8f32c204f9
--- /dev/null
+++ b/test/fixtures/expression_equality/log10.b.json
@@ -0,0 +1,4 @@
+[
+  "log10",
+  101
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/log2.a.json b/test/fixtures/expression_equality/log2.a.json
new file mode 100644
index 0000000000..95cdc15373
--- /dev/null
+++ b/test/fixtures/expression_equality/log2.a.json
@@ -0,0 +1,4 @@
+[
+  "log2",
+  1024
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/log2.b.json b/test/fixtures/expression_equality/log2.b.json
new file mode 100644
index 0000000000..2fffaeb32a
--- /dev/null
+++ b/test/fixtures/expression_equality/log2.b.json
@@ -0,0 +1,4 @@
+[
+  "log2",
+  1025
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/match.a.json b/test/fixtures/expression_equality/match.a.json
new file mode 100644
index 0000000000..ba8afc4126
--- /dev/null
+++ b/test/fixtures/expression_equality/match.a.json
@@ -0,0 +1,12 @@
+[
+  "match",
+  [
+    "get",
+    "x"
+  ],
+  "a",
+  "Apple",
+  "b",
+  "Banana",
+  "Kumquat"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/match.b.json b/test/fixtures/expression_equality/match.b.json
new file mode 100644
index 0000000000..2404b8e2e7
--- /dev/null
+++ b/test/fixtures/expression_equality/match.b.json
@@ -0,0 +1,12 @@
+[
+  "match",
+  [
+    "get",
+    "x"
+  ],
+  "a",
+  "Apple",
+  "b",
+  "Banana",
+  "Kumquat_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/max.a.json b/test/fixtures/expression_equality/max.a.json
new file mode 100644
index 0000000000..09a8f82bd7
--- /dev/null
+++ b/test/fixtures/expression_equality/max.a.json
@@ -0,0 +1,6 @@
+[
+  "max",
+  0,
+  -1,
+  100
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/max.b.json b/test/fixtures/expression_equality/max.b.json
new file mode 100644
index 0000000000..1b0beb20d6
--- /dev/null
+++ b/test/fixtures/expression_equality/max.b.json
@@ -0,0 +1,6 @@
+[
+  "max",
+  0,
+  -1,
+  101
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/min.a.json b/test/fixtures/expression_equality/min.a.json
new file mode 100644
index 0000000000..38cc90f1cd
--- /dev/null
+++ b/test/fixtures/expression_equality/min.a.json
@@ -0,0 +1,5 @@
+[
+  "min",
+  ["get", "x"],
+  0
+]
diff --git a/test/fixtures/expression_equality/min.b.json b/test/fixtures/expression_equality/min.b.json
new file mode 100644
index 0000000000..84a5f66842
--- /dev/null
+++ b/test/fixtures/expression_equality/min.b.json
@@ -0,0 +1,5 @@
+[
+  "min",
+  ["get", "x"],
+  1
+]
diff --git a/test/fixtures/expression_equality/minus.a.json b/test/fixtures/expression_equality/minus.a.json
new file mode 100644
index 0000000000..9eb4f954e7
--- /dev/null
+++ b/test/fixtures/expression_equality/minus.a.json
@@ -0,0 +1,5 @@
+[
+  "-",
+  5,
+  7
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/minus.b.json b/test/fixtures/expression_equality/minus.b.json
new file mode 100644
index 0000000000..87042b98ef
--- /dev/null
+++ b/test/fixtures/expression_equality/minus.b.json
@@ -0,0 +1,5 @@
+[
+  "-",
+  5,
+  8
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/mod.a.json b/test/fixtures/expression_equality/mod.a.json
new file mode 100644
index 0000000000..8439bafcd1
--- /dev/null
+++ b/test/fixtures/expression_equality/mod.a.json
@@ -0,0 +1,5 @@
+[
+  "%",
+  18,
+  12
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/mod.b.json b/test/fixtures/expression_equality/mod.b.json
new file mode 100644
index 0000000000..362e1721c1
--- /dev/null
+++ b/test/fixtures/expression_equality/mod.b.json
@@ -0,0 +1,5 @@
+[
+  "%",
+  18,
+  13
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/not.a.json b/test/fixtures/expression_equality/not.a.json
new file mode 100644
index 0000000000..b5f03e0ac0
--- /dev/null
+++ b/test/fixtures/expression_equality/not.a.json
@@ -0,0 +1,10 @@
+[
+  "!",
+  [
+    "boolean",
+    [
+      "get",
+      "x"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/not.b.json b/test/fixtures/expression_equality/not.b.json
new file mode 100644
index 0000000000..a4d77adf2e
--- /dev/null
+++ b/test/fixtures/expression_equality/not.b.json
@@ -0,0 +1,10 @@
+[
+  "!",
+  [
+    "boolean",
+    [
+      "get",
+      "x_other"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/number.a.json b/test/fixtures/expression_equality/number.a.json
new file mode 100644
index 0000000000..57c3df48e7
--- /dev/null
+++ b/test/fixtures/expression_equality/number.a.json
@@ -0,0 +1,7 @@
+[
+  "number",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/number.b.json b/test/fixtures/expression_equality/number.b.json
new file mode 100644
index 0000000000..d1843362d3
--- /dev/null
+++ b/test/fixtures/expression_equality/number.b.json
@@ -0,0 +1,7 @@
+[
+  "number",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/object.a.json b/test/fixtures/expression_equality/object.a.json
new file mode 100644
index 0000000000..7551cfdbb2
--- /dev/null
+++ b/test/fixtures/expression_equality/object.a.json
@@ -0,0 +1,7 @@
+[
+  "object",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/object.b.json b/test/fixtures/expression_equality/object.b.json
new file mode 100644
index 0000000000..8444d40c0e
--- /dev/null
+++ b/test/fixtures/expression_equality/object.b.json
@@ -0,0 +1,7 @@
+[
+  "object",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/plus.a.json b/test/fixtures/expression_equality/plus.a.json
new file mode 100644
index 0000000000..a00c4409fa
--- /dev/null
+++ b/test/fixtures/expression_equality/plus.a.json
@@ -0,0 +1,7 @@
+[
+  "+",
+  1,
+  2,
+  3,
+  4
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/plus.b.json b/test/fixtures/expression_equality/plus.b.json
new file mode 100644
index 0000000000..87c071123f
--- /dev/null
+++ b/test/fixtures/expression_equality/plus.b.json
@@ -0,0 +1,7 @@
+[
+  "+",
+  1,
+  2,
+  3,
+  5
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/pow.a.json b/test/fixtures/expression_equality/pow.a.json
new file mode 100644
index 0000000000..c1a1e67f86
--- /dev/null
+++ b/test/fixtures/expression_equality/pow.a.json
@@ -0,0 +1,11 @@
+[
+  "^",
+  4,
+  [
+    "number",
+    [
+      "get",
+      "x"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/pow.b.json b/test/fixtures/expression_equality/pow.b.json
new file mode 100644
index 0000000000..ca5331b92a
--- /dev/null
+++ b/test/fixtures/expression_equality/pow.b.json
@@ -0,0 +1,11 @@
+[
+  "^",
+  4,
+  [
+    "number",
+    [
+      "get",
+      "x_other"
+    ]
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/rgb.a.json b/test/fixtures/expression_equality/rgb.a.json
new file mode 100644
index 0000000000..ce6c5e5dd0
--- /dev/null
+++ b/test/fixtures/expression_equality/rgb.a.json
@@ -0,0 +1,6 @@
+[
+  "rgb",
+  0,
+  0,
+  255
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/rgb.b.json b/test/fixtures/expression_equality/rgb.b.json
new file mode 100644
index 0000000000..577c19748b
--- /dev/null
+++ b/test/fixtures/expression_equality/rgb.b.json
@@ -0,0 +1,6 @@
+[
+  "rgb",
+  0,
+  0,
+  0
+]
diff --git a/test/fixtures/expression_equality/rgba.a.json b/test/fixtures/expression_equality/rgba.a.json
new file mode 100644
index 0000000000..e8ad7326c1
--- /dev/null
+++ b/test/fixtures/expression_equality/rgba.a.json
@@ -0,0 +1,7 @@
+[
+  "rgba",
+  0,
+  0,
+  255,
+  1
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/rgba.b.json b/test/fixtures/expression_equality/rgba.b.json
new file mode 100644
index 0000000000..81d442eaae
--- /dev/null
+++ b/test/fixtures/expression_equality/rgba.b.json
@@ -0,0 +1,7 @@
+[
+  "rgba",
+  0,
+  0,
+  255,
+  0.5
+]
diff --git a/test/fixtures/expression_equality/sin.a.json b/test/fixtures/expression_equality/sin.a.json
new file mode 100644
index 0000000000..0f7ae2966f
--- /dev/null
+++ b/test/fixtures/expression_equality/sin.a.json
@@ -0,0 +1,4 @@
+[
+  "sin",
+  0
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/sin.b.json b/test/fixtures/expression_equality/sin.b.json
new file mode 100644
index 0000000000..90f309b80f
--- /dev/null
+++ b/test/fixtures/expression_equality/sin.b.json
@@ -0,0 +1,4 @@
+[
+  "sin",
+  1
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/sqrt.a.json b/test/fixtures/expression_equality/sqrt.a.json
new file mode 100644
index 0000000000..56dd85bc1a
--- /dev/null
+++ b/test/fixtures/expression_equality/sqrt.a.json
@@ -0,0 +1,7 @@
+[
+  "sqrt",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/sqrt.b.json b/test/fixtures/expression_equality/sqrt.b.json
new file mode 100644
index 0000000000..ab05d5084c
--- /dev/null
+++ b/test/fixtures/expression_equality/sqrt.b.json
@@ -0,0 +1,7 @@
+[
+  "sqrt",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/step.a.json b/test/fixtures/expression_equality/step.a.json
new file mode 100644
index 0000000000..4fee85cd03
--- /dev/null
+++ b/test/fixtures/expression_equality/step.a.json
@@ -0,0 +1,18 @@
+[
+  "number",
+  [
+    "step",
+    [
+      "number",
+      [
+        "get",
+        "x"
+      ]
+    ],
+    11,
+    0,
+    111,
+    1,
+    1111
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/step.b.json b/test/fixtures/expression_equality/step.b.json
new file mode 100644
index 0000000000..0a591a84df
--- /dev/null
+++ b/test/fixtures/expression_equality/step.b.json
@@ -0,0 +1,18 @@
+[
+  "number",
+  [
+    "step",
+    [
+      "number",
+      [
+        "get",
+        "x"
+      ]
+    ],
+    11,
+    0,
+    111,
+    1,
+    1112
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/string.a.json b/test/fixtures/expression_equality/string.a.json
new file mode 100644
index 0000000000..a79344f338
--- /dev/null
+++ b/test/fixtures/expression_equality/string.a.json
@@ -0,0 +1,7 @@
+[
+  "string",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/string.b.json b/test/fixtures/expression_equality/string.b.json
new file mode 100644
index 0000000000..6f77f3c3cf
--- /dev/null
+++ b/test/fixtures/expression_equality/string.b.json
@@ -0,0 +1,7 @@
+[
+  "string",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/tan.a.json b/test/fixtures/expression_equality/tan.a.json
new file mode 100644
index 0000000000..c78e47e492
--- /dev/null
+++ b/test/fixtures/expression_equality/tan.a.json
@@ -0,0 +1,4 @@
+[
+  "tan",
+  0.7853981633974483
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/tan.b.json b/test/fixtures/expression_equality/tan.b.json
new file mode 100644
index 0000000000..c22e64cf8a
--- /dev/null
+++ b/test/fixtures/expression_equality/tan.b.json
@@ -0,0 +1,4 @@
+[
+  "tan",
+  1.7853981633974483
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/times.a.json b/test/fixtures/expression_equality/times.a.json
new file mode 100644
index 0000000000..ce6d9b46e0
--- /dev/null
+++ b/test/fixtures/expression_equality/times.a.json
@@ -0,0 +1,7 @@
+[
+  "*",
+  3,
+  2,
+  0.5,
+  2
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/times.b.json b/test/fixtures/expression_equality/times.b.json
new file mode 100644
index 0000000000..147e011172
--- /dev/null
+++ b/test/fixtures/expression_equality/times.b.json
@@ -0,0 +1,7 @@
+[
+  "*",
+  3,
+  2,
+  0.5,
+  3
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-boolean.a.json b/test/fixtures/expression_equality/to-boolean.a.json
new file mode 100644
index 0000000000..ccf48149ec
--- /dev/null
+++ b/test/fixtures/expression_equality/to-boolean.a.json
@@ -0,0 +1,7 @@
+[
+  "to-boolean",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-boolean.b.json b/test/fixtures/expression_equality/to-boolean.b.json
new file mode 100644
index 0000000000..7896261241
--- /dev/null
+++ b/test/fixtures/expression_equality/to-boolean.b.json
@@ -0,0 +1,7 @@
+[
+  "to-boolean",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-color.a.json b/test/fixtures/expression_equality/to-color.a.json
new file mode 100644
index 0000000000..de9ab59eec
--- /dev/null
+++ b/test/fixtures/expression_equality/to-color.a.json
@@ -0,0 +1,7 @@
+[
+  "to-color",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-color.b.json b/test/fixtures/expression_equality/to-color.b.json
new file mode 100644
index 0000000000..c0566ef6a7
--- /dev/null
+++ b/test/fixtures/expression_equality/to-color.b.json
@@ -0,0 +1,7 @@
+[
+  "to-color",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-number.a.json b/test/fixtures/expression_equality/to-number.a.json
new file mode 100644
index 0000000000..65b2df5014
--- /dev/null
+++ b/test/fixtures/expression_equality/to-number.a.json
@@ -0,0 +1,7 @@
+[
+  "to-number",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-number.b.json b/test/fixtures/expression_equality/to-number.b.json
new file mode 100644
index 0000000000..b38dc5a455
--- /dev/null
+++ b/test/fixtures/expression_equality/to-number.b.json
@@ -0,0 +1,7 @@
+[
+  "to-number",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-string.a.json b/test/fixtures/expression_equality/to-string.a.json
new file mode 100644
index 0000000000..66f9a9caa1
--- /dev/null
+++ b/test/fixtures/expression_equality/to-string.a.json
@@ -0,0 +1,7 @@
+[
+  "to-string",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/to-string.b.json b/test/fixtures/expression_equality/to-string.b.json
new file mode 100644
index 0000000000..977a9d7769
--- /dev/null
+++ b/test/fixtures/expression_equality/to-string.b.json
@@ -0,0 +1,7 @@
+[
+  "to-string",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/typeof.a.json b/test/fixtures/expression_equality/typeof.a.json
new file mode 100644
index 0000000000..7843ff8c7f
--- /dev/null
+++ b/test/fixtures/expression_equality/typeof.a.json
@@ -0,0 +1,7 @@
+[
+  "typeof",
+  [
+    "get",
+    "x"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/typeof.b.json b/test/fixtures/expression_equality/typeof.b.json
new file mode 100644
index 0000000000..412482347a
--- /dev/null
+++ b/test/fixtures/expression_equality/typeof.b.json
@@ -0,0 +1,7 @@
+[
+  "typeof",
+  [
+    "get",
+    "x_other"
+  ]
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/upcase.a.json b/test/fixtures/expression_equality/upcase.a.json
new file mode 100644
index 0000000000..d12ca7b08d
--- /dev/null
+++ b/test/fixtures/expression_equality/upcase.a.json
@@ -0,0 +1,4 @@
+[
+  "upcase",
+  "string"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/upcase.b.json b/test/fixtures/expression_equality/upcase.b.json
new file mode 100644
index 0000000000..ddeeb0300c
--- /dev/null
+++ b/test/fixtures/expression_equality/upcase.b.json
@@ -0,0 +1,4 @@
+[
+  "upcase",
+  "string_other"
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/zoom.a.json b/test/fixtures/expression_equality/zoom.a.json
new file mode 100644
index 0000000000..fc675721ab
--- /dev/null
+++ b/test/fixtures/expression_equality/zoom.a.json
@@ -0,0 +1,13 @@
+[
+  "interpolate",
+  [
+    "linear"
+  ],
+  [
+    "zoom"
+  ],
+  0,
+  0,
+  30,
+  30
+]
\ No newline at end of file
diff --git a/test/fixtures/expression_equality/zoom.b.json b/test/fixtures/expression_equality/zoom.b.json
new file mode 100644
index 0000000000..6314858a5e
--- /dev/null
+++ b/test/fixtures/expression_equality/zoom.b.json
@@ -0,0 +1,13 @@
+[
+  "interpolate",
+  [
+    "linear"
+  ],
+  [
+    "zoom"
+  ],
+  0,
+  0,
+  30,
+  31
+]
\ No newline at end of file
diff --git a/test/fixtures/style_parser/expressions.info.json b/test/fixtures/style_parser/expressions.info.json
new file mode 100644
index 0000000000..9e1765ecd0
--- /dev/null
+++ b/test/fixtures/style_parser/expressions.info.json
@@ -0,0 +1,12 @@
+{
+    "default": {
+        "log": [
+            [1, "WARNING", "ParseStyle", "Expected color but found number instead."],
+            [1, "WARNING", "ParseStyle", "[2]: Expected number but found string instead."],
+            [1, "WARNING", "ParseStyle", "\"zoom\" expression may only be used as input to a top-level \"step\" or \"interpolate\" expression."],
+            [1, "WARNING", "ParseStyle", "value must be a string"],
+            [1, "WARNING", "ParseStyle", "property expressions not supported"],
+            [1, "WARNING", "ParseStyle", "Type array<number> is not interpolatable."]
+        ]
+    }
+}
diff --git a/test/fixtures/style_parser/expressions.style.json b/test/fixtures/style_parser/expressions.style.json
new file mode 100644
index 0000000000..b9b4aeac7f
--- /dev/null
+++ b/test/fixtures/style_parser/expressions.style.json
@@ -0,0 +1,74 @@
+{
+  "version": 8,
+  "sources": {
+    "source": {
+      "type": "vector",
+      "url": "mapbox://mapbox.mapbox-streets-v5"
+    }
+  },
+  "layers": [
+    {
+      "id": "valid expression",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": ["rgba", 10, ["number", ["get", "x"]], 30, 1]
+      }
+    },
+    {
+      "id": "invalid expression type - color",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": ["pi"]
+      }
+    },
+    {
+      "id": "invalid expression - fails type checking",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": ["rgba", 1, "should be a number", 0, 1]
+      }
+    },
+    {
+      "id": "invalid expression - nested zoom expression",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-opacity": ["+", 0.5, ["interpolate", ["linear"], ["zoom"], 0, 0, 1, 1]]
+      }
+    },
+    {
+      "id": "invalid expression - not allowed in visibility",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "layout": {
+        "visibility": ["literal", true]
+      }
+    },
+    {
+      "id": "invalid expression - not a DDS property",
+      "type": "fill-extrusion",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-extrusion-opacity": ["get", "opacity"]
+      }
+    },
+    {
+      "id": "invalid expression - line-dasharray must use step interpolation",
+      "type": "line",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "line-dasharray": ["interpolate", ["linear"], ["zoom"], 0, ["literal", [1, 2]], 1, ["literal", [3, 4]]]
+      }
+    }
+  ]
+}
diff --git a/test/style/conversion/function.test.cpp b/test/style/conversion/function.test.cpp
index 9e8a6b3a7f..a48be2c075 100644
--- a/test/style/conversion/function.test.cpp
+++ b/test/style/conversion/function.test.cpp
@@ -3,6 +3,8 @@
 #include <mbgl/style/conversion/json.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/function.hpp>
+#include <mbgl/style/conversion/data_driven_property_value.hpp>
+#include <mbgl/util/rapidjson.hpp>
 
 using namespace mbgl;
 using namespace mbgl::style;
@@ -50,3 +52,29 @@ TEST(StyleConversion, Function) {
     ASSERT_FALSE(fn9);
     ASSERT_EQ("function base must be a number", error.message);
 }
+
+TEST(StyleConversion, CompositeFunctionExpression) {
+    Error error;
+
+    auto parseFunction = [&](const std::string& src) {
+        JSDocument doc;
+        doc.Parse<0>(src);
+        return convert<DataDrivenPropertyValue<float>>(doc, error);
+    };
+
+    auto fn1 = parseFunction(R"(["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10])");
+    ASSERT_TRUE(fn1);
+    
+    auto fn2 = parseFunction(R"(["coalesce", ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10], 0])");
+    ASSERT_TRUE(fn2);
+
+    auto fn3 = parseFunction(R"(["let", "a", 0, ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10] ])");
+    ASSERT_TRUE(fn3);
+
+    auto fn4 = parseFunction(R"(["coalesce", ["let", "a", 0, ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10], 0 ])");
+    ASSERT_TRUE(fn4);
+
+    auto fn5 = parseFunction(R"(["coalesce", ["interpolate", ["linear"], ["number", ["get", "x"]], 0, ["zoom"], 10, 10], 0])");
+    ASSERT_FALSE(fn5);
+    ASSERT_EQ(R"("zoom" expression may only be used as input to a top-level "step" or "interpolate" expression.)", error.message);
+}
diff --git a/test/style/expression/expression.test.cpp b/test/style/expression/expression.test.cpp
new file mode 100644
index 0000000000..694569695c
--- /dev/null
+++ b/test/style/expression/expression.test.cpp
@@ -0,0 +1,91 @@
+#include <mbgl/test/util.hpp>
+#include <mbgl/util/io.hpp>
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/util/rapidjson.hpp>
+#include <mbgl/style/rapidjson_conversion.hpp>
+#include <mbgl/style/expression/is_expression.hpp>
+
+#include <rapidjson/document.h>
+
+#include <iostream>
+#include <fstream>
+#include <dirent.h>
+
+
+using namespace mbgl;
+using namespace mbgl::style;
+
+TEST(Expression, IsExpression) {
+    rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> spec;
+    spec.Parse<0>(util::read_file("mapbox-gl-js/src/style-spec/reference/v8.json").c_str());
+    ASSERT_FALSE(spec.HasParseError());
+    ASSERT_TRUE(spec.IsObject() &&
+                spec.HasMember("expression_name") &&
+                spec["expression_name"].IsObject() &&
+                spec["expression_name"].HasMember("values") &&
+                spec["expression_name"]["values"].IsObject());
+    
+    const auto& allExpressions = spec["expression_name"]["values"];
+    
+    for(auto& entry : allExpressions.GetObject()) {
+        const std::string name { entry.name.GetString(), entry.name.GetStringLength() };
+        JSDocument document;
+        document.Parse<0>(R"([")" + name + R"("])");
+
+        const JSValue* expression = &document;
+        EXPECT_TRUE(expression::isExpression(conversion::Convertible(expression))) << name;
+    }
+}
+
+class ExpressionEqualityTest : public ::testing::TestWithParam<std::string> {};
+
+TEST_P(ExpressionEqualityTest, ExpressionEquality) {
+    const std::string base = std::string("test/fixtures/expression_equality/") + GetParam();
+
+    std::string error;
+    auto parse = [&](std::string filename, std::string& error_) -> std::unique_ptr<expression::Expression> {
+        rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> document;
+        document.Parse<0>(util::read_file(filename).c_str());
+        assert(!document.HasParseError());
+        const JSValue* expression = &document;
+        expression::ParsingContext ctx;
+        expression::ParseResult parsed = ctx.parse(conversion::Convertible(expression));
+        if (!parsed) {
+            error_ = ctx.getErrors().size() > 0 ? ctx.getErrors()[0].message : "failed to parse";
+        };
+        return std::move(*parsed);
+    };
+
+    std::unique_ptr<expression::Expression> expression_a1 = parse(base + ".a.json", error);
+    ASSERT_TRUE(expression_a1) << GetParam() << ": " << error;
+
+    std::unique_ptr<expression::Expression> expression_a2 = parse(base + ".a.json", error);
+    ASSERT_TRUE(expression_a2) << GetParam() << ": " << error;
+
+    std::unique_ptr<expression::Expression> expression_b = parse(base + ".b.json", error);
+    ASSERT_TRUE(expression_b) << GetParam() << ": " << error;
+
+
+    EXPECT_TRUE(*expression_a1 == *expression_a2);
+    EXPECT_TRUE(*expression_a1 != *expression_b);
+}
+
+INSTANTIATE_TEST_CASE_P(Expression, ExpressionEqualityTest, ::testing::ValuesIn([] {
+    std::vector<std::string> names;
+    const std::string ending = ".a.json";
+
+    const std::string style_directory = "test/fixtures/expression_equality";
+    DIR *dir = opendir(style_directory.c_str());
+    if (dir != nullptr) {
+        for (dirent *dp = nullptr; (dp = readdir(dir)) != nullptr;) {
+            const std::string name = dp->d_name;
+            if (name.length() >= ending.length() && name.compare(name.length() - ending.length(), ending.length(), ending) == 0) {
+                names.push_back(name.substr(0, name.length() - ending.length()));
+            }
+        }
+        closedir(dir);
+    }
+
+    EXPECT_GT(names.size(), 0u);
+    return names;
+}()));
diff --git a/test/style/expression/util.test.cpp b/test/style/expression/util.test.cpp
new file mode 100644
index 0000000000..0337cd871f
--- /dev/null
+++ b/test/style/expression/util.test.cpp
@@ -0,0 +1,23 @@
+#include <mbgl/test/util.hpp>
+#include <mbgl/style/expression/util.hpp>
+
+using namespace mbgl;
+using namespace mbgl::style::expression;
+
+TEST(Expression, Util_rgba) {
+    Result<Color> valid = rgba(0, 0, 0, 0);
+    ASSERT_TRUE(valid);
+    ASSERT_EQ(valid->r, 0);
+    ASSERT_EQ(valid->g, 0);
+    ASSERT_EQ(valid->b, 0);
+    ASSERT_EQ(valid->a, 0);
+
+    ASSERT_FALSE(rgba(0, 0, 0, -0.1));
+    ASSERT_FALSE(rgba(0, 0, 0, 1.1));
+    ASSERT_FALSE(rgba(0, 0, -1, 1));
+    ASSERT_FALSE(rgba(0, 0, 256, 1));
+    ASSERT_FALSE(rgba(0, -1, 0, 1));
+    ASSERT_FALSE(rgba(0, 256, 0, 1));
+    ASSERT_FALSE(rgba(-1, 1, 0, 1));
+    ASSERT_FALSE(rgba(-256, 1, 0, 1));
+}