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d9d82fb0af
See the section `do notation` in the manual for more info. * nkMacroStmt has been removed Macro statements are now mapped to regular nkCall nodes. The support for additional clauses (such as else, except, of, etc) have been restored - they will now appear as additional arguments for the nkCall node (as nkElse, nkExcept, etc nodes) * fixed some regressions in the `is` operator and semCompiles
104 lines
2.4 KiB
Nim
104 lines
2.4 KiB
Nim
discard """
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file: "tusingstatement.nim"
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output: "Using test.Closing test."
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"""
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import
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macros
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# This macro mimics the using statement from C#
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#
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# XXX:
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# It doen't match the C# version exactly yet.
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# In particular, it's not recursive, which prevents it from dealing
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# with exceptions thrown from the variable initializers when multiple.
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# variables are used.
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#
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# Also, since nimrod relies less on exceptions in general, a more
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# idiomatic definition could be:
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# var x = init()
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# if opened(x):
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# try:
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# body
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# finally:
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# close(x)
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#
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# `opened` here could be an overloaded proc which any type can define.
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# A common practice can be returing an Optional[Resource] obj for which
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# `opened` is defined to `optional.hasValue`
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macro using(e: expr): stmt {.immediate.} =
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let e = callsite()
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if e.len != 3:
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error "Using statement: unexpected number of arguments. Got " &
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$e.len & ", expected: 1 or more variable assignments and a block"
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var args = e
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var body = e[2]
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var
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variables : seq[PNimrodNode]
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closingCalls : seq[PNimrodNode]
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newSeq(variables, 0)
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newSeq(closingCalls, 0)
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for i in countup(1, args.len-2):
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if args[i].kind == nnkExprEqExpr:
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var varName = args[i][0]
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var varValue = args[i][1]
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var varAssignment = newNimNode(nnkIdentDefs)
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varAssignment.add(varName)
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varAssignment.add(newNimNode(nnkEmpty)) # empty means no type
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varAssignment.add(varValue)
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variables.add(varAssignment)
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closingCalls.add(newCall(!"close", varName))
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else:
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error "Using statement: Unexpected expression. Got " &
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$args[i].kind & " instead of assignment."
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var varSection = newNimNode(nnkVarSection)
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varSection.add(variables)
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var finallyBlock = newNimNode(nnkStmtList)
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finallyBlock.add(closingCalls)
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# XXX: Use a template here once getAst is working properly
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var targetAst = parseStmt"""block:
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var
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x = foo()
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y = bar()
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try:
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body()
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finally:
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close x
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close y
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"""
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targetAst[0][1][0] = varSection
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targetAst[0][1][1][0] = body
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targetAst[0][1][1][1][0] = finallyBlock
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result = targetAst
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type
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TResource* = object
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field*: string
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proc openResource(param: string): TResource =
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result.field = param
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proc close(r: var TResource) =
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write(stdout, "Closing " & r.field & ".")
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proc use(r: var TResource) =
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write(stdout, "Using " & r.field & ".")
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using(r = openResource("test")):
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use r
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