| 1 | package calc |
| 2 | |
| 3 | import ( |
| 4 | "math" |
| 5 | "strconv" |
| 6 | "strings" |
| 7 | ) |
| 8 | |
| 9 | // evalBinary evaluates both operands unconditionally (formulas have no |
| 10 | // side effects to order), then propagates the left operand's error if it |
| 11 | // is one, else the right's — "left-most wins" when both sides are errors. |
| 12 | func evalBinary(t *Binary, env Env) Value { |
| 13 | l := Eval(t.Left, env) |
| 14 | r := Eval(t.Right, env) |
| 15 | if l.Kind == KindErr { |
| 16 | return l |
| 17 | } |
| 18 | if r.Kind == KindErr { |
| 19 | return r |
| 20 | } |
| 21 | switch t.Op { |
| 22 | case "+", "-", "*", "/", "^": |
| 23 | return evalArith(t.Op, l, r) |
| 24 | case "&": |
| 25 | return evalConcat(l, r) |
| 26 | default: // "=", "<>", "<", "<=", ">", ">=" |
| 27 | return evalCompare(t.Op, l, r) |
| 28 | } |
| 29 | } |
| 30 | |
| 31 | // evalArith coerces both operands to numbers and applies op. Coercion |
| 32 | // failure on the left operand wins over one on the right, keeping |
| 33 | // "left-most wins" consistent even below the Value level. |
| 34 | func evalArith(op string, l, r Value) Value { |
| 35 | ln, errKind := toNumber(l) |
| 36 | if errKind != ErrNone { |
| 37 | return Value{Kind: KindErr, Err: errKind} |
| 38 | } |
| 39 | rn, errKind := toNumber(r) |
| 40 | if errKind != ErrNone { |
| 41 | return Value{Kind: KindErr, Err: errKind} |
| 42 | } |
| 43 | switch op { |
| 44 | case "+": |
| 45 | return Value{Kind: KindNum, Num: ln + rn} |
| 46 | case "-": |
| 47 | return Value{Kind: KindNum, Num: ln - rn} |
| 48 | case "*": |
| 49 | return Value{Kind: KindNum, Num: ln * rn} |
| 50 | case "/": |
| 51 | if rn == 0 { |
| 52 | return Value{Kind: KindErr, Err: ErrDiv0} |
| 53 | } |
| 54 | return Value{Kind: KindNum, Num: ln / rn} |
| 55 | default: // "^" |
| 56 | return Value{Kind: KindNum, Num: math.Pow(ln, rn)} |
| 57 | } |
| 58 | } |
| 59 | |
| 60 | // evalConcat implements "&": both operands render as text (Excel's own |
| 61 | // coercion — TRUE, FALSE, and a number's plain decimal form) and join. |
| 62 | func evalConcat(l, r Value) Value { |
| 63 | return Value{Kind: KindStr, Str: toStr(l) + toStr(r)} |
| 64 | } |
| 65 | |
| 66 | // evalCompare implements the six comparison operators over compareValues' |
| 67 | // ordering. |
| 68 | func evalCompare(op string, l, r Value) Value { |
| 69 | c := compareValues(l, r) |
| 70 | var result bool |
| 71 | switch op { |
| 72 | case "=": |
| 73 | result = c == 0 |
| 74 | case "<>": |
| 75 | result = c != 0 |
| 76 | case "<": |
| 77 | result = c < 0 |
| 78 | case "<=": |
| 79 | result = c <= 0 |
| 80 | case ">": |
| 81 | result = c > 0 |
| 82 | default: // ">=" |
| 83 | result = c >= 0 |
| 84 | } |
| 85 | return Value{Kind: KindBool, Bool: result} |
| 86 | } |
| 87 | |
| 88 | // compareValues orders l against r the way Excel's comparison operators |
| 89 | // do. A blank cell first coerces to whatever "nothing" means for the |
| 90 | // *other* side's kind — 0 against a number, "" against text, FALSE |
| 91 | // against a boolean, so blank = 0, blank = "", and blank = FALSE all read |
| 92 | // TRUE, matching Excel — and two blanks compare equal outright. Neither |
| 93 | // substitution changes the Value stored anywhere; it only affects this |
| 94 | // one comparison, which is why an empty cell still counts as empty to |
| 95 | // COUNT/COUNTA (task 8) even though "=" treats it as equal to 0. |
| 96 | // |
| 97 | // Once neither side is empty: within the same kind, numbers compare |
| 98 | // numerically, text compares case-insensitively (Excel's default — |
| 99 | // "abc" = "ABC"), and booleans order false before true. Across kinds, |
| 100 | // every number sorts below every piece of text, and every piece of text |
| 101 | // sorts below every boolean, regardless of the text's literal content — |
| 102 | // the string "9" is still greater than the number 100, because it is |
| 103 | // text, not because of what it says. |
| 104 | func compareValues(l, r Value) int { |
| 105 | if l.Kind == KindEmpty && r.Kind == KindEmpty { |
| 106 | return 0 |
| 107 | } |
| 108 | if l.Kind == KindEmpty { |
| 109 | l = emptyAs(r.Kind) |
| 110 | } |
| 111 | if r.Kind == KindEmpty { |
| 112 | r = emptyAs(l.Kind) |
| 113 | } |
| 114 | lr, rr := typeRank(l), typeRank(r) |
| 115 | if lr != rr { |
| 116 | if lr < rr { |
| 117 | return -1 |
| 118 | } |
| 119 | return 1 |
| 120 | } |
| 121 | switch l.Kind { |
| 122 | case KindStr: |
| 123 | return strings.Compare(strings.ToUpper(l.Str), strings.ToUpper(r.Str)) |
| 124 | case KindBool: |
| 125 | switch { |
| 126 | case l.Bool == r.Bool: |
| 127 | return 0 |
| 128 | case !l.Bool: |
| 129 | return -1 |
| 130 | default: |
| 131 | return 1 |
| 132 | } |
| 133 | default: // KindNum |
| 134 | switch { |
| 135 | case l.Num < r.Num: |
| 136 | return -1 |
| 137 | case l.Num > r.Num: |
| 138 | return 1 |
| 139 | default: |
| 140 | return 0 |
| 141 | } |
| 142 | } |
| 143 | } |
| 144 | |
| 145 | // emptyAs returns the identity value a blank cell coerces to when |
| 146 | // compared against a cell of kind k, so compareValues never has to rank |
| 147 | // KindEmpty itself against KindNum/KindStr/KindBool. |
| 148 | func emptyAs(k ValueKind) Value { |
| 149 | switch k { |
| 150 | case KindStr: |
| 151 | return Value{Kind: KindStr, Str: ""} |
| 152 | case KindBool: |
| 153 | return Value{Kind: KindBool, Bool: false} |
| 154 | default: // KindNum (KindEmpty vs KindEmpty is handled before this is called) |
| 155 | return Value{Kind: KindNum, Num: 0} |
| 156 | } |
| 157 | } |
| 158 | |
| 159 | // typeRank orders the value kinds for cross-kind comparison: number, |
| 160 | // then text, then boolean. Never called with KindEmpty — compareValues |
| 161 | // substitutes it away first via emptyAs. |
| 162 | func typeRank(v Value) int { |
| 163 | switch v.Kind { |
| 164 | case KindStr: |
| 165 | return 1 |
| 166 | case KindBool: |
| 167 | return 2 |
| 168 | default: // KindNum |
| 169 | return 0 |
| 170 | } |
| 171 | } |
| 172 | |
| 173 | // toNumber coerces v for an arithmetic operator: an empty cell as 0 |
| 174 | // (Excel's own arithmetic coercion for a blank), a number as itself, a |
| 175 | // boolean as 1/0, and text only if it parses as a number outright (no |
| 176 | // currency symbols, percent signs or thousands separators — that |
| 177 | // normalization belongs to whatever task parses user input into a |
| 178 | // formula, not to evaluation). Never called on a KindErr Value: callers |
| 179 | // check for an error operand before coercing. |
| 180 | func toNumber(v Value) (float64, ErrKind) { |
| 181 | switch v.Kind { |
| 182 | case KindEmpty: |
| 183 | return 0, ErrNone |
| 184 | case KindNum: |
| 185 | return v.Num, ErrNone |
| 186 | case KindBool: |
| 187 | if v.Bool { |
| 188 | return 1, ErrNone |
| 189 | } |
| 190 | return 0, ErrNone |
| 191 | case KindStr: |
| 192 | n, err := strconv.ParseFloat(strings.TrimSpace(v.Str), 64) |
| 193 | if err != nil { |
| 194 | return 0, ErrValue |
| 195 | } |
| 196 | return n, ErrNone |
| 197 | default: |
| 198 | return 0, ErrValue |
| 199 | } |
| 200 | } |
| 201 | |
| 202 | // toStr renders v as text for "&" concatenation: an empty cell as "" (not |
| 203 | // "0" — this is the whole reason KindEmpty exists as its own kind rather |
| 204 | // than collapsing into KindNum{0}), a string as itself, a number in its |
| 205 | // plain decimal form (no thousands separator or currency — display |
| 206 | // formatting is a concern outside this package), a boolean as TRUE/FALSE. |
| 207 | func toStr(v Value) string { |
| 208 | switch v.Kind { |
| 209 | case KindEmpty: |
| 210 | return "" |
| 211 | case KindStr: |
| 212 | return v.Str |
| 213 | case KindBool: |
| 214 | if v.Bool { |
| 215 | return "TRUE" |
| 216 | } |
| 217 | return "FALSE" |
| 218 | default: // KindNum |
| 219 | return strconv.FormatFloat(v.Num, 'g', -1, 64) |
| 220 | } |
| 221 | } |
| 222 | |
amadan