dimgigov
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72 lines
2.1 KiB
Nim
72 lines
2.1 KiB
Nim
## This module implements a little helper macro to ease
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## writing the dispatching logic for JSON based servers.
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import macros
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proc tbody(n: NimNode): NimNode =
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# transforms::
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# f fields(a, "b")
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# into::
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# f a = %args["a"], b = %args["b"]
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case n.kind
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of nnkCallKinds:
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result = copyNimNode(n)
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result.add tbody(n[0])
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for i in 1..<n.len:
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let it = n[i]
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if it.kind == nnkCall and $it[0] == "fields":
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for j in 1..<it.len:
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let field = it[j]
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let s = if field.kind in {nnkStrLit..nnkTripleStrLit}: field.strVal
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else: $field
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let arg = newTree(nnkPrefix, ident"%",
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newTree(nnkBracketExpr, ident"arg", newLit(s)))
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result.add newTree(nnkExprEqExpr, ident(s), arg)
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else:
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result.add tbody(it)
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else:
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result = copyNimNode(n)
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for x in n: result.add tbody(x)
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macro createDispatcher*(name, n: untyped): untyped =
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expectKind n, nnkStmtList
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result = newStmtList()
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let disp = newTree(nnkCaseStmt, ident"cmd")
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template cmdProc(name, body) {.dirty.} =
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proc name(arg: JsonNode): JsonNode = body
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template callCmd(name) {.dirty.} =
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result = name(arg)
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for x in n:
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if x.kind == nnkCall and x.len == 2 and
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x[0].kind == nnkIdent and x[1].kind == nnkStmtList:
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result.add getAst(cmdProc(x[0], tbody x[1]))
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disp.add newTree(nnkOfBranch, newLit($x[0]),
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newStmtList(getAst(callCmd(x[0]))))
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else:
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# do not touch:
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result.add n
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disp.add newTree(nnkElse, newStmtList(newTree(nnkDiscardStmt, newEmptyNode())))
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template dispatchProc(name, body) {.dirty.} =
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proc dispatch(inp: JsonNode): JsonNode =
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let arg = inp["arg"]
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let cmd = inp["cmd"].getStr("")
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body
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result.add getAst(dispatchProc(name, disp))
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when defined(debugDispatcherDsl):
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echo repr result
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when isMainModule:
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import json, db_sqlite
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createDispatcher(dispatch):
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insertCustomer:
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echo "insert customer", fields(a, b, c)
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result = arg
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selectCustomers:
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echo "select customer"
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result = arg
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echo dispatch(nil, %*{"cmd": "insertCustomer", "arg": [1, 2, 3]})
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