skip WHITESPACE '\s+'

token NUM           '[0-9]+'
token VAR           '[A-Za-z_][A-Za-z0-9_]*'

token OP            '\+|-'
token MOP           '\*|/'

token IN            '==>'
token OUT           '<=='
token ASSIGN         '->'

token LOOP          '\?\?'
token IF             '\?'
token ELSE           '\|'

token LPAREN        '\('
token RPAREN        '\)'
token LBRACE        '\{'
token RBRACE        '\}'
token SEMI          ';'

token OP '\+|-'
token MOP '\*|/'

%

<program> ::= <stmtlist>

<stmtlist> **= <stmt>

<stmt>InputStmt ::= <IN> <VAR> <SEMI>
<stmt>OutputStmt ::= <OUT> <exp> <SEMI>
<stmt>AssignStmt ::= <VAR> <ASSIGN> <exp> <SEMI>

<stmt>ControlStmt ::= <LPAREN> <exp> <RPAREN> <ctrltail>

<ctrltail>IfStmt ::= <IF> <block> <ELSE> <block>
<ctrltail>LoopStmt ::= <LOOP> <block>

<block> ::= <LBRACE> <stmtlist> <RBRACE>

<exp> ::= <mult> <exprest>
<exprest> **= <OP> <mult>
<mult> ::= <value> <multrest>
<multrest> **= <MOP> <value>
<value> ::= <NUM> | <VAR>

%