From 29f797efae8e4712f27d9e8613f3d19d6ee06b90 Mon Sep 17 00:00:00 2001
From: Alessandro Coglio <coglio@kestrel.edu>
Date: Fri, 15 Apr 2022 19:54:41 -0700
Subject: [PATCH] [ABNF] Add (first draft of) input grammar.

This is the (sub)grammar for input files. It is an initial draft, written based
on the Notion page 'Leo Input File Doc/Spec'. This should be compared with the
currently implemented parser of input (i.e. .in) files.

As the Leo Reference will describe (that part has not been written yet), the
input grammar is based on the lexical grammar, i.e. an input file consists of
tokens, comments, and whitespace. However, only some tokens (compared to the
syntactic grammar for Leo code files) are used, namely the ones reachable from
the `input-file` nonterminal.

Currently (i.e. im this initial version of Leo) `input-type` is (any) `type` and
`input-expression` is just a `literal`, but these may evolve as we extend the
language (e.g. we'll probably disallow circuit types and allow tuple and array
constructions). The intent is that `input-type` will be a subset of `type` and
that `input-expression` will be a subset of `expression`.
---
 docs/grammar/README.md        | 56 ++++++++++++++++++++++++++++++++++-
 docs/grammar/abnf-grammar.txt | 18 +++++++++++
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/docs/grammar/README.md b/docs/grammar/README.md
index 4522f663a9..9eaa014ba9 100644
--- a/docs/grammar/README.md
+++ b/docs/grammar/README.md
@@ -148,6 +148,7 @@ keyword = %s"address"
         / %s"char"
         / %s"console"
         / %s"const"
+        / %s"constant"
         / %s"else"
         / %s"field"
         / %s"for"
@@ -399,6 +400,7 @@ symbol = "!" / "&&" / "||"
        / "+" / "-" / "*" / "/" / "**"
        / "="
        / "(" / ")"
+       / "[" / "]"
        / "{" / "}"
        / "," / "." / ".." / ";" / ":" / "?"
        / "->" / "_"
@@ -805,7 +807,7 @@ Go to: _[function-parameter](#user-content-function-parameter)_;
 
 <a name="function-parameter"></a>
 ```abnf
-function-parameter = [ %s"public" / %s"const" ] identifier ":" type
+function-parameter = [ %s"public" / %s"constant" / %s"const" ] identifier ":" type
 ```
 
 Go to: _[identifier](#user-content-identifier), [type](#user-content-type)_;
@@ -866,4 +868,56 @@ Go to: _[format-string-close-brace](#user-content-format-string-close-brace), [f
 <a name="format-string"></a>
 ```abnf
 format-string = *format-string-element
+```
+
+
+--------
+
+
+Input Grammar
+-------------
+
+<a name="input-type"></a>
+```abnf
+input-type = type
+```
+
+Go to: _[type](#user-content-type)_;
+
+
+<a name="input-expression"></a>
+```abnf
+input-expression = literal
+```
+
+Go to: _[literal](#user-content-literal)_;
+
+
+<a name="input-item"></a>
+```abnf
+input-item = identifier ":" input-type "=" input-expression ";"
+```
+
+Go to: _[identifier](#user-content-identifier), [input-expression](#user-content-input-expression), [input-type](#user-content-input-type)_;
+
+
+<a name="input-title"></a>
+```abnf
+input-title = "[" identifier "]"
+```
+
+Go to: _[identifier](#user-content-identifier)_;
+
+
+<a name="input-section"></a>
+```abnf
+input-section = input-title *input-item
+```
+
+Go to: _[input-title](#user-content-input-title)_;
+
+
+<a name="input-file"></a>
+```abnf
+input-file = *input-section
 
diff --git a/docs/grammar/abnf-grammar.txt b/docs/grammar/abnf-grammar.txt
index 5b91993063..c8db7517c9 100644
--- a/docs/grammar/abnf-grammar.txt
+++ b/docs/grammar/abnf-grammar.txt
@@ -177,6 +177,7 @@ symbol = "!" / "&&" / "||"
        / "+" / "-" / "*" / "/" / "**"
        / "="
        / "(" / ")"
+       / "[" / "]"
        / "{" / "}"
        / "," / "." / ".." / ";" / ":" / "?"
        / "->" / "_"
@@ -346,3 +347,20 @@ format-string-element = not-brace
                       / format-string-close-brace
 
 format-string = *format-string-element
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+; Input Grammar
+; -------------
+
+input-type = type
+
+input-expression = literal
+
+input-item = identifier ":" input-type "=" input-expression ";"
+
+input-title = "[" identifier "]"
+
+input-section = input-title *input-item
+
+input-file = *input-section