token.peg

# This code is hereby placed in the public domain.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHORS ''AS IS'' AND ANY EXPRESS
# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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# BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
# OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
# EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

%prefix "calc"

statement <- _ e:expression _ EOL { puts "answer=#{e}" }
           / ( !EOL . )* EOL      { warn "error\n" }

expression <- e:term { $$ = e; }

term <- l:term _ PLUS  _ r:term   { $$ = l + r }
      / l:term _ MINUS _ r:factor { $$ = l - r }
      / e:factor                  { $$ = e }

factor <- l:factor _ MUL _ r:unary { $$ = l * r }
        / l:factor _ DIV _ r:unary { $$ = l / r }
        / e:unary                  { $$ = e }

unary <- PLUS  _ e:unary { $$ = +e }
       / MINUS _ e:unary { $$ = -e }
       / e:primary       { $$ = e }

primary <- primary:PRIMARY { $$ = primary }
         / LPAREN _ e:expression _ RPAREN { $$ = e }

_ <- SPACES?

# token is described by the subset of PEG.
# ex. "123 + 456" will be tokenized "\x01\x09\x03\x09\x01" and {0 => 123, 4 => 456}
#                                    |   pos: 0      |   pos: 4
#                                    +-> value: 123  +-> value: 456

PRIMARY  <-- < [0-9]+ > { $$ = $1.to_i }
EOL      <-- '\n' / '\r\n' / '\r' / ';'
PLUS     <-- '+'
MINUS    <-- '-'
MUL      <-- '*'
DIV      <-- '/'
LPAREN   <-- '('
RPAREN   <-- ')'
SPACES   <-- [ \t]*

# define parser rules implicitly:
# PRIMARY  <- '\x01'
# EOL      <- '\x02'
# PLUS     <- '\x03'
# MINUS    <- '\x04'
# MUL      <- '\x05'
# DIV      <- '\x06'
# LPAREN   <- '\x07'
# RPAREN   <- '\x08'
# SPACES   <- '\x09'

%%

if ARGV[0]
  require "stringio"
  str = ARGV[0]
  $stdin = StringIO.new("#{str}\n", "r")
end
Calc.new.run