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+# Foi Language AST Specification
+## Program
+A Foi Language Program consists of a body and comments.
+```javascript
+{
+  "type": "Program",
+  "body": [],
+}
+```
+### Comments
+Single line comments are written as
+```javascript
+// hello
+```
+`AST`.  
+```javascript
+"leadingComments": [
+    {
+        "type": "Line",
+        "value": " hello",
+        "range": [
+        0,
+        8
+        ]
+    }
+]
+```
+### Variables
+**Variable Declaration:**
+```javascript
+def x: empty;
+```
+`AST`.
+```
+type: "VariableDeclaration",
+"start": 0,
+"end": 13,
+"declarations": [
+    {
+        "type": "VariableDeclarator",
+        "start": 4,
+        "end": 12,
+        "id": {
+          "type": "Identifier",
+          "start": 4,
+          "end": 5,
+          "name": "x"
+        },
+        "init": {
+            "type": "Literal",
+            "start": 7,
+            "end": 12,
+            "value": null,
+            "raw": "empty"
+        }
+    }
+]
+```
+**Variable Reassignment:**
+```javascript
+x <: 1;
+```
+`AST`.
+```
+{
+    "type": "ExpressionStatement",
+    "start": 17,
+    "end": 25,
+    "id": {
+        "type": "BinaryCallExpression",
+        "start": 4,
+        "end": 5,
+        "callee": {
+            "type": "Identifier",
+            "start": 2,
+            "end": 3,
+            "name": "<:"
+        },
+        "arguments": [
+            {
+                "type": "Identifier",
+                "start": 0,
+                "end": 0,
+                "name": "x"
+            },
+            {
+                "type": "Literal",
+                "start": 5,
+                "end": 5,
+                "value": 1,
+                "raw": "1"
+            }
+        ]
+    },
+    "value": {
+        "type": "Literal",
+        "start": 11,
+        "end": 15,
+        "value": 1,
+        "raw": "1"
+    }
+}
+```
+**Function calls**
+```javascript
+log("hello")
+```
+`AST`
+```
+{
+  "type": "ExpressionStatement",
+  "expression": {
+    "type": "CallExpression",
+    "callee": {
+      "type": "Identifier",
+      "name": "log"
+    },
+    "arguments": [
+      {
+        "type": "Literal",
+        "value": "hello",
+        "raw": "\"hello\""
+      }
+    ]
+  }
+}
+```
+**Function calls**
+```javascript
+| log "hello" |
+```
+`AST`
+```
+{
+  "type": "ExpressionStatement",
+  "expression": {
+    "type": "EvalCallExpression",
+    "callee": {
+      "type": "Identifier",
+      "name": "log"
+    },
+    "arguments": [
+      {
+        "type": "Literal",
+        "value": "hello",
+        "raw": "\"hello\""
+      }
+    ]
+  }
+}
+```
+```javascript
+| log | + 2, 3 ||
+```
+```
+{
+      "type": "ExpressionStatement",
+      "expression": {
+        "type": "EvalCallExpression",
+        "callee": {
+          "type": "Identifier",
+          "name": "log"
+        },
+        "arguments": [
+          {
+            "type": "EvalCallExpression",
+            "callee": {
+              "type": "Identifier",
+              "name": "+"
+            },
+            "arguments": [
+              {
+                "type": "Literal",
+                "value": 2,
+                "raw": "2"
+              },
+              {
+                "type": "Literal",
+                "value": 3,
+                "raw": "3"
+              }
+            ]
+          }
+        ]
+      }
+    }
+```
+**Reverse Function Call Order**
+```javascript
+| |'- | 1, 6 |
+| '- 1, 6 |
+```
+```
+{
+  "type": "ExpressionStatement",
+  "expression": {
+    "type": "UnaryExpression",
+    "operator": "'",
+    "argument": {
+        "type": "EvalCallExpression",
+        "callee": {
+          "type": "Identifier",
+          "name": "-"
+        },
+        "arguments": [
+          {
+            "type": "Literal",
+            "value": 1,
+            "raw": "1"
+          },
+          {
+            "type": "Literal",
+            "value": 6,
+            "raw": "6"
+          }
+        ]
+    },
+  }
+}
+```
+**Partial Function Application**
+```javascript
+// where `+` has an arity of 2
+| + 2 |
+```
+```
+{
+  "type": "ExpressionStatement",
+  "expression": {
+    "type": "PartialCallApplication",
+    "callee": {
+      "type": "Identifier",
+      "name": "+"
+    },
+    "arguments": [
+      {
+        "type": "Literal",
+        "value": 2,
+        "raw": "2"
+      }
+    ]
+  }
+}
+```
+```javascript
+| | + 2 | 2 | // 4
+```
+`AST`
+```
+{
+  "type": "EvalCallExpression",
+  "callee": {
+    "type": "PartialCallApplication",
+    "callee": {
+      "type": "Identifier",
+      "name": "+"
+    },
+    "arguments": [
+      {
+        "type": "Literal",
+        "value": 2,
+        "raw": "2"
+      }
+    ]
+  },
+  "arguments": [
+    {
+      "type": "Literal",
+      "value": 2,
+      "raw": "2"
+    }
+  ]
+}
+```
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