Data commit

Task/Arithmetic-evaluation/Factor/arithmetic-evaluation.factor

@@ -0,0 +1,42 @@
+USING: accessors kernel locals math math.parser peg.ebnf ;
+IN: rosetta.arith
+
+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 ]]
+;EBNF
+
+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 ;