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Contents
# Grammar for simple arithmetical expressions
require 'rley' # Load the gem
########################################
# Define a grammar for basic arithmetical expressions
builder = Rley::Syntax::GrammarBuilder.new do
add_terminals('NUMBER')
add_terminals('LPAREN', 'RPAREN') # For '(', ')' delimiters
add_terminals('PLUS', 'MINUS') # For '+', '-' operators or sign
add_terminals('STAR', 'DIVIDE') # For '*', '/' operators
rule 'expression' => %w(sign simple_expression)
rule 'simple_expression' => 'term'
rule 'simple_expression' => %w(simple_expression add_operator term)
rule 'term' => 'factor'
rule 'term' => %w(term mul_operator factor)
rule 'factor' => 'NUMBER'
rule 'factor' => %w(LPAREN expression RPAREN)
rule 'sign' => 'PLUS'
rule 'sign' => 'MINUS'
rule 'sign' => []
rule 'add_operator' => 'PLUS'
rule 'add_operator' => 'MINUS'
rule 'mul_operator' => 'STAR'
rule 'mul_operator' => 'DIVIDE'
end
# And now build the grammar...
CalcGrammar = builder.grammar
Version data entries
8 entries across 8 versions & 1 rubygems