This is the Backus-Naur form of PL:

Program = Block ".".
Block = "begin" DefinitionPart StatementPart "end".
DefinitionPart = { Definition ";" }.
Definition = ConstantDefinition | VariableDefinition |                                                                                                                     
   ProcedureDefinition .
ConstantDefinition = "const" ConstantName "=" Constant .
VariableDefinition = TypeSymbol VariableList |   
   TypeSymbol "array" VariableList "[" Constant "]" .
TypeSymbol = "integer" | "Boolean"
VariableList = VariableName { "," VariableName } .
ProcedureDefinition = "proc"  ProcedureName Block .
StatementPart = { Statement ";" } .
Statement =
   EmptyStatement | ReadStatement | WriteStatement |
   AssignmentStatement | ProcedureStatement |
   IfStatement | DoStatement .
EmptyStatement = "skip" .
ReadStatement = "read" VariableAccessList .
VariableAccessList = VariableAccess {"," VariableAccess } .
WriteStatement = "write" ExpressionList .
ExpressionList = Expression {"," Expression } .
AssignmentStatement = 
   VariableAccessList ":=" ExpressionList .
ProcedureStatement = "call" ProcedureName .
IfStatement = "if" GuardedCommandList "fi" .
DoStatement = "do" GuardedCommandList "od" .
GuardedCommandList =
   GuardedCommand { "[]" GuardedCommand } .
GuardedCommand = Expression "->" StatementPart .
Expression = PrimaryExpression 
   { PrimaryOperator PrimaryExpression } .
PrimaryOperator = "&" | "|" .
PrimaryExpression = SimpleExpression
   [ RelationalOperator SimpleExpression ] .
RelationalOperator = "<" | "=" | ">" .
SimpleExpression =
   [ "-" ] Term { AddingOperator Term } .
AddingOperator = "+" | "-" .
Term = Factor { MultiplyingOperator Factor } .
MultiplyingOperator = "*" | "/" | "\" .
Factor = Constant | VariableAccess | 
   "(" Expression ")" | "~" Factor .
VariableAccess = VariableName [ IndexedSelector ] .
IndexedSelector = "[" Expression "]" .
Constant = Numeral | BooleanSymbol | ConstantName .
Numeral = Digit { Digit } .
BooleanSymbol = "false" | "true" .
Name = Letter { Letter | Digit | "_" } .