我正在开发一个使用Happy解析器生成器的项目。目前为止,我的工作如下:
Exp : Exp1 { $1 }
Exp1 : Exp1 '+' Term { \p -> $1 p + $3 p }
| Exp1 '-' Term { \p -> $1 p - $3 p }
| Term { $1 }
Term : Term '*' Factor { \p -> $1 p * $3 p }
| Term '/' Factor { \p -> $1 p / $3 p }
| sqrt Factor { \p -> sqrt $2 p }
| Factor { $1 }
Factor
: double { \p -> $1 }
| '(' Exp ')' { $2 }
问题是我遇到了以下错误:
Parser.hs:158:38:
No instance for (Floating ([a0] -> Double))
arising from a use of `happyReduction_7'
Possible fix:
add an instance declaration for (Floating ([a0] -> Double))
In the second argument of `happySpecReduce_2', namely
`happyReduction_7'
In the expression: happySpecReduce_2 6 happyReduction_7
In an equation for `happyReduce_7':
happyReduce_7 = happySpecReduce_2 6 happyReduction_7
你知道我该怎么解决这个问题吗?
更新:我已经解决了,但是现在只有当我写成“sqrt2”(sqrt和2之间没有空格)时它才起作用;如果我写成“sqrt 2”,我会得到“解析错误”。
以下是我在Alex(lex)文件中的内容:
tokens :-
$white+ ;
"--".* ;
"sqrt" { \s -> TokenSqrt}
"sin" { \s -> TokenSin}
"log" { \s -> TokenLog}
@doubleNumber { \s -> TokenDouble (read s) }
@var { \s -> TokenVar s }
"+" { \s -> TokenPlus }
"-" { \s -> TokenMinus }
"*" { \s -> TokenMul }
"/" { \s -> TokenDiv }
"(" { \s -> TokenOB }
")" { \s -> TokenCB }
"=" { \s -> TokenEq }
sqrt $ $2 p
,不是吗? - muhmuhten{ sqrt . $2 }
而不是{ \p -> sqrt ($2 p) }
是否有效呢? - muhmuhten