factor/extra/rosetta-code/arithmetic-evaluation/arithmetic-evaluation.factor

70 lines
2.0 KiB
Factor
Raw Normal View History

USING: accessors kernel locals math math.parser multiline peg.ebnf ;
IN: rosetta-code.arithmetic-evaluation
! http://rosettacode.org/wiki/Arithmetic_evaluation
! Create a program which parses and evaluates arithmetic
! expressions.
! Requirements
! * An abstract-syntax tree (AST) for the expression must be
! created from parsing the input.
! * The AST must be used in evaluation, also, so the input may not
! be directly evaluated (e.g. by calling eval or a similar
! language feature.)
! * The expression will be a string or list of symbols like
! "(1+3)*7".
! * The four symbols + - * / must be supported as binary operators
! with conventional precedence rules.
! * Precedence-control parentheses must also be supported.
! Note
! For those who don't remember, mathematical precedence is as
! follows:
! * Parentheses
! * Multiplication/Division (left to right)
! * Addition/Subtraction (left to right)
TUPLE: operator left right ;
TUPLE: add < operator ; C: <add> add
TUPLE: sub < operator ; C: <sub> sub
TUPLE: mul < operator ; C: <mul> mul
TUPLE: div < operator ; C: <div> div
EBNF: expr-ast [=[
spaces = [\n\t ]*
digit = [0-9]
number = (digit)+ => [[ string>number ]]
value = spaces number:n => [[ n ]]
| spaces "(" exp:e spaces ")" => [[ e ]]
fac = fac:a spaces "*" value:b => [[ a b <mul> ]]
| fac:a spaces "/" value:b => [[ a b <div> ]]
| value
exp = exp:a spaces "+" fac:b => [[ a b <add> ]]
| exp:a spaces "-" fac:b => [[ a b <sub> ]]
| fac
main = exp:e spaces !(.) => [[ e ]]
]=]
GENERIC: eval-ast ( ast -- result )
M: number eval-ast ;
: recursive-eval ( ast -- left-result right-result )
[ left>> eval-ast ] [ right>> eval-ast ] bi ;
M: add eval-ast recursive-eval + ;
M: sub eval-ast recursive-eval - ;
M: mul eval-ast recursive-eval * ;
M: div eval-ast recursive-eval / ;
: evaluate ( string -- result )
expr-ast eval-ast ;