feat: document grammar of expressions

src/pages/spec/ast/ast.md

@@ -20,11 +20,20 @@ Module = (Statement | Expression)*
 
 ## Statement
 
-(At the moment) a statement is either a variable binding or a function declaration
+A statement is either a variable binding, a function declaration,
+a conditional (for now, until those becom expressions),
+for loop, while loop, or an assignment.
+
+Assignment includes the operators `= += -= *= /=`, etc. Those operators
+cannot be used elsewhere, only as part of an Assignment.
 
 ```ebnf
 Statement = VariableBinding
           | FunctionDeclaration
+          | Conditional
+          | ForLoop
+          | WhileLoop
+          | Assignment
 ```
 
 ## Expression
@@ -61,3 +70,22 @@ BlockMember = Statement
 ```
 
 
+## Assignment
+
+The target of an assignment can only be an identifier for now.
+In the future this will include other things like maps, arrays,
+pattern matching, destructuring, etc.
+
+```ebnf
+Assignment         = AssignmentTarget, AssignmentOperator, Expression
+
+AssignmentTarget   = Identifier
+AssignmentOperator = "="
+                   | "+="
+                   | "-="
+                   | "*/"
+                   | "/="
+                   | "%="
+```
+
+

src/pages/spec/ast/expression.md

@@ -5,4 +5,26 @@ title: Expression
 
 # Expression
 
-Expression
+The expression parser effectively implements a precedence table.
+
+| Operator   | Precedence |
+|------------|------------|
+| == !=      | 4          |
+| > >= < <=  | 3          |
+| - + ++     | 2          |
+| / * %      | 1          |
+
+
+
+```ebnf
+Expression = Equality
+
+Equality   = Comparison, (("==" | "!="),             Comparison)*
+Comparison = Term,       ((">" | ">=" | "<" | "<="), Term)*
+Term       = Factor,     (("-" | "+" | "++"),        Factor)*
+Factor     = Unary,      (("/" | "*" | "%"),         Unary)*
+Unary      = ("!" | "-"), Expression
+           | FunctionCallExpression
+```
+
+