feat(reference): Lexical Structure—Keywords

Author: ospencer

docs_config.yml

@@ -97,7 +97,7 @@ docs_groups:
     - reference/lexical_structure:
         - reference/lexical_structure/whitespace
         - reference/lexical_structure/comments
-  #     - reference/lexical_structure/keywords
+        - reference/lexical_structure/keywords
   #     - reference/lexical_structure/identifiers
   #     - reference/lexical_structure/literals
   #     - reference/lexical_structure/operators

src/reference/lexical_structure/keywords.md

@@ -0,0 +1,61 @@
+---
+title: Keywords
+---
+
+Languages typically classify keywords in three categories—strict, soft, and reserved.
+
+## Strict keywords
+
+Strict keywords can only be used where specified by the language and can never be used as identifiers. In Grain, these keywords are:
+
+```ebnf
+keyword =
+  | "assert"
+  | "break"
+  | "continue"
+  | "else"
+  | "enum"
+  | "except"
+  | "exception"
+  | "export"
+  | "fail"
+  | "false"
+  | "for"
+  | "foreign"
+  | "from"
+  | "if"
+  | "import"
+  | "let"
+  | "match"
+  | "mut"
+  | "primitive"
+  | "rec"
+  | "record"
+  | "throw"
+  | "true"
+  | "type"
+  | "void"
+  | "wasm"
+  | "when"
+  | "while"
+;
+```
+
+## Soft keywords
+
+Soft keywords are sometimes allowed be used as an identifier, depending on the context.
+
+Grain currently has no soft keywords.
+
+## Reserved keywords
+
+Reserved keywords are keywords that are not yet used by the language, but are disallowed as identifiers to allow programs to continue to be compatible with future versions of `grainc`.
+
+The reserved keywords are as follows:
+
+```ebnf
+reserved_keyword =
+  | "try"
+  | "catch"
+;
+```