evalExpr :=
  [ evalExpr' :=
      \str i . %unit? i (car str)
                      [ c := car i; i' := cdr i
                      . charNum? c (evalExpr' (cons (digitToInt c) str) i')
                                   (%unit? str ()
                                           [ a := car str; str1 := cdr str
                                           . eq? c '=' (evalExpr' (cons a str) i')
                                                       (%unit? str1 ()
                                                               [ b := car str1; str2 := cdr str1
                                                               . eq? c '+' (evalExpr' (cons (%add a b) str2) i') (
                                                                 eq? c '-' (evalExpr' (cons (%sub a b) str2) i') (
                                                                 eq? c '*' (evalExpr' (cons (%mul a b) str2) i') (
                                                                 eq? c '/' (evalExpr' (cons (%div a b) str2) i')))) ])])]
  . \i . %unit? i () (evalExpr' () i) ];

dropspaces := filter (\c . (and (ne? c '\n') (and (ne? c ' ') (ne? c '\t'))));

iowriteError :=
  iomapM_ %iowrite (cons 'e' (
                    cons 'r' (
                    cons 'r' (
                    cons 'o' (
                    cons 'r' (
                    cons '\n' ()))))));

main := %iobind ioreadLine \l .
        %unit? l (%ioreturn ())
                 (iobind_ [ r := evalExpr (dropspaces l)
                          . %unit? r
                                   iowriteError
                                   (iobind_ (iowriteDec r) (%iowrite '\n')) ]
                          main);