lib: journal: Add scalar multiplication and division

Author: ag-eitilt

hledger-lib/Hledger/Read/Common.hs

@@ -690,11 +690,12 @@ amountp' s =
 -- joined as an arithmetic expression.
 mamountp :: Bool -> JournalParser m MixedAmount
 mamountp requireOp = label "mixed amount" $ do
+  pos <- getOffset
   opc <- ( if requireOp
            then id
            else option '+'
          ) $ do
-    c <- satisfy (`elem` ("+-" :: String))
+    c <- oneOf ("+-" :: String)
     lift (skipMany spacenonewline)
     pure c
   paren <- option False $ try $ do
@@ -710,13 +711,40 @@ mamountp requireOp = label "mixed amount" $ do
     else do
       inner <- amountp
       pure $ Mixed [inner]
+  mult <- multiplierp pos
   tail <- option nullmixedamt $ try $ do
     lift (skipMany spacenonewline)
     mamountp True
   let op = case opc of
         '-' -> negate
         _   -> id
-  return $ op amount + tail
+  return $ multiplyMixedAmount mult (op amount) + tail
+
+multiplierp :: Int -> JournalParser m Quantity
+multiplierp startOffset = do
+  lift (skipMany spacenonewline)
+  c <- optional $ try $ oneOf ("*/" :: String)
+  case c of
+    Nothing -> return 1
+    Just c' -> do
+      lift (skipMany spacenonewline)
+      (m, _, _, _) <- lift $ numberp Nothing
+      endOffset <- getOffset
+      f <- if c' == '/'
+        then if m == 0
+             then dividebyzeroerr startOffset endOffset
+             -- The "Decimal" docs recommend against using '(/)', but the
+             -- alternate interface provided might be more cumbersome than
+             -- necessary for this circumstance, as it would require
+             -- keeping track of multiple potential results.  Maybe revisit
+             -- this as part of a larger patch focused on fair rounding?
+             else return (/ m)
+        else return (* m)
+      ms <- multiplierp startOffset
+      return $ f ms
+
+dividebyzeroerr :: Int -> Int -> JournalParser m a
+dividebyzeroerr startOffset endOffset = customFailure $ parseErrorAtRegion startOffset endOffset "attempted division by 0"
 
 -- | Parse a mixed amount from a string, or get an error.
 mamountp' :: String -> MixedAmount
@@ -1376,6 +1404,7 @@ tests_Common = tests "Common" [
 
   ,tests "mamountp" [
     test "basic"                         $ expectParseEq (mamountp False) "$47.18"                           $ Mixed [usd 47.18]
+   ,test "operations"                    $ expectParseEq (mamountp False) "$6.00 + $5.00 - $4.00 / 2 * 3"    $ Mixed [usd 5.00]
    ,test "multiple commodities"          $ expectParseEq (mamountp False) "$47.18+€20,59"                    $ Mixed [
        amount{
           acommodity="$"

tests/journal/amount-expressions.test

@@ -135,7 +135,27 @@ hledger -f - print --auto
 >>>2
 >>>=0
 
-# 9. Standard postings may not be headed by multipliers
+# 9. Modifiers operate on all commodities in a posting
+hledger -f - print --auto
+<<<
+= a
+    (c)           *-1 + $8
+
+2018-01-01
+    a              $5 - 5 CAD
+    b
+>>>
+2018/01/01
+    a                $5
+    a            -5 CAD
+    (c)              $3
+    (c)           5 CAD
+    b
+
+>>>2
+>>>=0
+
+# 10. Standard postings may not be headed by multipliers
 hledger -f - print
 <<<
 2018-01-01
@@ -145,7 +165,7 @@ hledger -f - print
 >>>2 /unexpected '*'/
 >>>=1
 
-# 10. Auto-postings require an operator between multiplier and expression
+# 11. Auto-postings require an operator between multiplier and expression
 # The error message could be a bit more helpful, but at least it mentions
 # expecting a mixed amount
 hledger -f - print --auto
@@ -161,3 +181,148 @@ hledger -f - print --auto
 >>>2 /unexpected '8'/
 >>>=1
 
+# 12. Multiplication by plain values works as expected
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 * 2
+    b             -$2 * 0.5
+    c              $2 * -1
+    d             -$1 * -1
+>>>
+2018/01/01
+    a              $2
+    b             $-1
+    c             $-2
+    d              $1
+
+>>>2
+>>>=0
+
+# 13. ... as does division
+hledger -f - print
+<<<
+2018-01-01
+    a           $2.00 / 2
+    b          -$1.00 / 0.5
+    c           $2.00 / -1
+    d          -$3.00 / -1
+>>>
+2018/01/01
+    a           $1.00
+    b          $-2.00
+    c          $-2.00
+    d           $3.00
+
+>>>2
+>>>=0
+
+# 14. Multiplication disallows commodities before the multiplier
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 * $2
+    c
+>>>
+>>>2 /unexpected '\$'/
+>>>=1
+
+# 15. ... and after
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 * 2 CAD
+    c
+>>>
+>>>2 /unexpected 'C'/
+>>>=1
+
+# 16. Division prevents divide-by-zero errors
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 / 0
+    b
+>>>
+>>>2 /division by 0/
+>>>=1
+
+# 17. ... but multiplication just simplifies them
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 * 0
+    b
+>>>
+2018/01/01
+    a               0
+    b
+
+>>>2
+>>>=0
+
+# 18. Multiplication and division rounds values according to the multiplicand precision
+hledger -f - print
+<<<
+2018-01-01
+    a              $3 * 0.5
+    b              $1 / 3
+    c
+>>>
+2018/01/01
+    a              $2
+    b               0
+    c
+
+>>>2
+>>>=0
+
+# 19. Commodity directives affect multiplication and division rounding
+hledger -f - print
+<<<
+commodity $1,000.00
+
+2018-01-01
+    a              $3 * 0.5
+    b              $1 / 3
+    c
+>>>
+2018/01/01
+    a           $1.50
+    b           $0.33
+    c
+
+>>>2
+>>>=0
+
+# 20. Expressions respect order of operations
+hledger -f - print
+<<<
+2018-01-01
+    a              $1 + $2  * 3 - $4
+    b             ($1 + $2) * 3 - $4
+    c
+>>>
+2018/01/01
+    a              $3
+    b              $5
+    c
+
+>>>2
+>>>=0
+
+# 21. Multiplication and division work over multiple commodities
+hledger -f - print
+<<<
+2018-01-01
+    a             ($1 + 2 CAD) * 3
+    b
+>>>
+2018/01/01
+    a              $3
+    a           6 CAD
+    b
+
+>>>2
+>>>=0
+