Merge pull request #338 from quantified-uncertainty/grammar-new110-26

grammar document

packages/website/docs/Internal/Grammar.md

@@ -0,0 +1,56 @@
+---
+title: Grammar
+author:
+  - Quinn Dougherty
+---
+
+Formal grammar specification, reference material for parser implementation.
+
+_In all likelihood the reference will have to be debugged as we see what tests pass and don't pass during implementation_.
+
+## Lexical descriptions of constants and identifiers
+
+```
+<number> ::= [-]? [0-9]+ (.[0-9]+)? | [-]? [0-9]+ (.[0-9]+)? [e] [-]? [0-9]+
+<symbol> ::= [a-zA-Z]+ [a-zA-Z0-9]?
+<bool> ::= true | false
+```
+
+## Expressions
+
+The following gives no typing information. You can obey the grammar and still write nonsensical code.
+
+Think of javascript's list unpacking notation to read our variable-argument function `mixture`.
+
+```
+<expr> ::= <term> + <expr> | <term> - <expr> | <expr> .+ <expr> | <expr> .- <expr> | <term>
+<term> ::= <power> * <term> | <power> <term> | <power> / <term> | <power> .* <term> | <power ./ <term> | <power>
+<power> ::= <factor> ^ <power> | <factor> .^ <power> | <factor>
+<factor> ::= <number> | <bool> | <symbol> | ( <expr> ) | <array> | <record> | <record>.<symbol> | <symbol> => <expr> | <symbol>(<symbol>) | <symbol>(<symbol>, <symbol>) | ...
+```
+
+## Data structures
+
+```
+<array> ::= [] | [<expr>] | [<expr>, <expr>] | ...
+<record> ::= {} | {<symbol>: <expr>} | {<symbol>: <expr>, <symbol>: <expr>} | ...
+```
+
+## Statements
+
+```
+<statement> ::= <assign> | <assignFunction>
+<assign> ::= <symbol> = <expr>
+<assignFunction> ::= <symbol>(<symbol>) = <expr> | <symbol>(<symbol>, <symbol>) = <expr> | ...
+```
+
+## A squiggle file
+
+To be valid and raise no errors as of current (apr22) interpreter,
+
+```
+<delim> ::= ; | \n
+<code> ::= <expr> | <statement> <delim> <expr> | <statement> <delim> <statement> <delim> <expr> | ...
+```
+
+This isn't strictly speaking true; the interpreter allows expressions outside of the final line.