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问题描述
我正在用Standard ML编写解释器,但是该函数的语法有问题,我无法弄清楚出了什么问题.
I'm writing an interpreter in Standard ML but I'm having trouble with my the syntax in this function, and I cannot figure out what's wrong.
以下是相关代码:
| eval (rho, SetExp (name, value)) = (case rhoContains rho name of true => rhoSet rho name value (rho, value) | false => globalSet (name, value)) fun rhoSet [] key value = [(key, value)] | rhoSet ((elt as (k, v)) :: tail) key value = if key = k then (key, value) :: tail else elt :: rhoSet tail key value fun rhoContains rho name = case rhoGet rho name of SOME _ => true | NONE => false这是SetExp的来源:
This is where SetExp comes from:
datatype expression = SetExp of (string * expression)运行此命令会给我列出很多错误,但是我认为这是相关的部分.第62行是eval中以true开头的行:
Running this gives me a long list of errors but I think this is the relevant section. Line 62 is the line that starts with true in eval:
eval.sml:62: error: Type error in function application. Function: rhoSet rho name value : (string * expression) list Argument: (rho, value) : (string * expression) list * expression Reason: Value being applied does not have a function type推荐答案
您要将太多参数传递给rhoSet-删除尾随对.
You're passing too many arguments to rhoSet - remove the trailing pair.
| eval (rho, SetExp (name, value)) = (case rhoContains rho name of true => rhoSet rho name value | false => globalSet (name, value))您还可以通过条件使此内容更具可读性:
You can also make this more readable with a conditional:
| eval (rho, SetExp (name, value)) = if rhoContains rho name then rhoSet rho name value else globalSet (name, value)更多推荐
为什么会出现这些错误,我该如何解决?
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