nandi/cosmicnim · d1e3be7

⑂ d1e3be7

Say why the calculator is in an error state

The error was a bool, so the only thing the display could offer was
"Error" — true but useless. It is now an enum whose values are their own
messages, surfaced in the caption row that was just reserved: the big
display still says Error, the line above it says why.

That also made a second failure worth naming. A result past what a float64
can hold used to become inf and print as a lone infinity sign; it now
reports being out of range, which is the same kind of answer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nandithebull committed 2026-09-20T12:04:15-07:00 Browse files

d1e3be7 parent: a561f5a

modified examples/calculator.nim +24 -6 Viewed

@@ -12,6 +12,13 @@ type
12	12	Op = enum
13	13	opNone = "", opAdd = "+", opSub = "−", opMul = "×", opDiv = "÷"
14	14
	15	+ CalcError* = enum
	16	+ ## The display can only ever say "Error", so the reason rides alongside
	17	+ ## it. Each value is its own message.
	18	+ errNone = ""
	19	+ errDivZero = "Cannot divide by zero"
	20	+ errRange = "Result is out of range"
	21	+
15	22	Key = object
16	23	label: string
17	24	id: int32
@@ -22,7 +29,7 @@ type
22	29	acc: float
23	30	pending: Op
24	31	startNew: bool ## next digit starts a fresh entry
25		- error: bool
	32	+ error: CalcError
26	33
27	34	const
28	35	Cols = 4
@@ -89,8 +96,14 @@ proc current(c: Calc): float =
89	96	## What the display is showing, as a number.
90	97	if c.entry.len > 0: parseFloat(c.entry) else: c.acc
91	98
	99	+proc failed*(c: Calc): bool = c.error != errNone
	100	+
	101	+proc reason*(c: Calc): string =
	102	+ ## Why the display says Error, or "" when it does not.
	103	+ $c.error
	104	+
92	105	proc display*(c: Calc): string =
93		- if c.error: "Error"
	106	+ if c.failed: "Error"
94	107	elif c.entry.len > 0: c.entry
95	108	else: format(c.acc)
96	109
@@ -103,8 +116,12 @@ proc resolve(c: var Calc) =
103	116	of opSub: c.acc = c.acc - rhs
104	117	of opMul: c.acc = c.acc * rhs
105	118	of opDiv:
106		- if rhs == 0.0: c.error = true
	119	+ if rhs == 0.0: c.error = errDivZero
107	120	else: c.acc = c.acc / rhs
	121	+ # Catch a result that has run off the end of what a float can say, so it
	122	+ # shows a reason rather than silently becoming inf or NaN.
	123	+ if c.error == errNone and (c.acc != c.acc or abs(c.acc) == Inf):
	124	+ c.error = errRange
108	125	c.entry = ""
109	126
110	127	proc digit(c: var Calc; d: int32) =
@@ -121,7 +138,7 @@ proc onPress*(ctx: pointer; id: int32) {.cdecl.} =
121	138	if id == IdClear:
122	139	c[] = newCalc()
123	140	return
124		- if c.error:
	141	+ if c[].failed:
125	142	return
126	143
127	144	case id
@@ -135,7 +152,7 @@ proc onPress*(ctx: pointer; id: int32) {.cdecl.} =
135	152	if '.' notin c.entry: c.entry.add '.'
136	153	of IdAdd, IdSub, IdMul, IdDiv:
137	154	c[].resolve()
138		- if not c.error:
	155	+ if not c[].failed:
139	156	c.pending = case id
140	157	of IdAdd: opAdd
141	158	of IdSub: opSub
@@ -215,7 +232,8 @@ proc onView(ctx: pointer; b: Builder; width, height: cfloat) {.cdecl.} =
215	232	# occupy its space either way or the whole keypad shifts.
216	233	b.size(-1.0, CaptionH)
217	234	b.text(
218		- if c.pending != opNone and not c.error: &"{format(c.acc)} {c.pending}"
	235	+ if c[].failed: c[].reason
	236	+ elif c.pending != opNone: &"{format(c.acc)} {c.pending}"
219	237	else: "",
220	238	TextCaption)
221	239

    Op = enum
      opNone = "", opAdd = "+", opSub = "−", opMul = "×", opDiv = "÷"
++  CalcError* = enum
++    ## The display can only ever say "Error", so the reason rides alongside
++    ## it. Each value is its own message.
++    errNone = ""
++    errDivZero = "Cannot divide by zero"
++    errRange = "Result is out of range"
++
    Key = object
      label: string
      id: int32
      acc: float
      pending: Op
      startNew: bool  ## next digit starts a fresh entry
--    error: bool
++    error: CalcError
  const
    Cols = 4
    ## What the display is showing, as a number.
    if c.entry.len > 0: parseFloat(c.entry) else: c.acc
++proc failed*(c: Calc): bool = c.error != errNone
++
++proc reason*(c: Calc): string =
++  ## Why the display says Error, or "" when it does not.
++  $c.error
++
  proc display*(c: Calc): string =
--  if c.error: "Error"
++  if c.failed: "Error"
    elif c.entry.len > 0: c.entry
    else: format(c.acc)
    of opSub: c.acc = c.acc - rhs
    of opMul: c.acc = c.acc * rhs
    of opDiv:
--    if rhs == 0.0: c.error = true
++    if rhs == 0.0: c.error = errDivZero
      else: c.acc = c.acc / rhs
++  # Catch a result that has run off the end of what a float can say, so it
++  # shows a reason rather than silently becoming inf or NaN.
++  if c.error == errNone and (c.acc != c.acc or abs(c.acc) == Inf):
++    c.error = errRange
    c.entry = ""
  proc digit(c: var Calc; d: int32) =
    if id == IdClear:
      c[] = newCalc()
      return
--  if c.error:
++  if c[].failed:
      return
    case id
      if '.' notin c.entry: c.entry.add '.'
    of IdAdd, IdSub, IdMul, IdDiv:
      c[].resolve()
--    if not c.error:
++    if not c[].failed:
        c.pending = case id
          of IdAdd: opAdd
          of IdSub: opSub
      # occupy its space either way or the whole keypad shifts.
      b.size(-1.0, CaptionH)
      b.text(
--      if c.pending != opNone and not c.error: &"{format(c.acc)} {c.pending}"
++      if c[].failed: c[].reason
++      elif c.pending != opNone: &"{format(c.acc)} {c.pending}"
        else: "",
        TextCaption)

modified tests/tcalculator.nim +19 -0 Viewed

@@ -38,10 +38,29 @@ suite "calculator":
38	38	test "division by zero errors, and only C recovers":
39	39	var c = fresh()
40	40	check c.press(1, IdDiv, 0, IdEquals) == "Error"
	41	+ check c.reason == "Cannot divide by zero"
41	42	check c.press(5) == "Error" # other keys are ignored
	43	+ check c.reason == "Cannot divide by zero"
42	44	check c.press(IdClear) == "0"
	45	+ check c.reason == "" # cleared along with the error
43	46	check c.press(7) == "7" # usable again
44	47
	48	+ test "a result too large to represent says so, rather than showing inf":
	49	+ var c = fresh()
	50	+ # Each pass multiplies by ~1e18; float64 gives up a little past 1e308.
	51	+ discard c.press(9, IdMul, 9, IdEquals)
	52	+ for _ in 1 .. 20:
	53	+ discard c.press(IdMul, 9, 9, 9, 9, 9, 9, 9, 9, 9, IdEquals)
	54	+ discard c.press(IdMul, 9, 9, 9, 9, 9, 9, 9, 9, 9, IdEquals)
	55	+ check c.display == "Error"
	56	+ check c.reason == "Result is out of range"
	57	+
	58	+ test "a healthy calculation has no reason":
	59	+ var c = fresh()
	60	+ check c.press(2, IdAdd, 2, IdEquals) == "4"
	61	+ check c.reason == ""
	62	+ check not c.failed
	63	+
45	64	test "decimals":
46	65	var c = fresh()
47	66	check c.press(1, IdDot, 5, IdAdd, 2, IdDot, 2, 5, IdEquals) == "3.75"

    test "division by zero errors, and only C recovers":
      var c = fresh()
      check c.press(1, IdDiv, 0, IdEquals) == "Error"
++    check c.reason == "Cannot divide by zero"
      check c.press(5) == "Error"          # other keys are ignored
++    check c.reason == "Cannot divide by zero"
      check c.press(IdClear) == "0"
++    check c.reason == ""                 # cleared along with the error
      check c.press(7) == "7"              # usable again
++  test "a result too large to represent says so, rather than showing inf":
++    var c = fresh()
++    # Each pass multiplies by ~1e18; float64 gives up a little past 1e308.
++    discard c.press(9, IdMul, 9, IdEquals)
++    for _ in 1 .. 20:
++      discard c.press(IdMul, 9, 9, 9, 9, 9, 9, 9, 9, 9, IdEquals)
++      discard c.press(IdMul, 9, 9, 9, 9, 9, 9, 9, 9, 9, IdEquals)
++    check c.display == "Error"
++    check c.reason == "Result is out of range"
++
++  test "a healthy calculation has no reason":
++    var c = fresh()
++    check c.press(2, IdAdd, 2, IdEquals) == "4"
++    check c.reason == ""
++    check not c.failed
++
    test "decimals":
      var c = fresh()
      check c.press(1, IdDot, 5, IdAdd, 2, IdDot, 2, 5, IdEquals) == "3.75"