# std/genasts

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This module implements AST generation using captured variables for macros.

# Imports

macros

# Types

    GenAstOpt = enum
      kDirtyTemplate, kNoNewLit

  Source Edit

# Macros

    macro genAstOpt(options: static set[GenAstOpt]; args: varargs[untyped]): untyped

  Accepts a list of captured variables `a=b` or `a` and a block and returns the AST that represents it. Local `{.inject.}` symbols (e.g. procs) are captured unless `kDirtyTemplate in options`.

  Example:

      # This example shows how one could write a simplified version of `unittest.check`.
      import std/[macros, strutils]
      macro check2(cond: bool): untyped =
        assert cond.kind == nnkInfix, "$# not implemented" % $cond.kind
        result = genAst(cond, s = repr(cond), lhs = cond[1], rhs = cond[2]):
          # each local symbol we access must be explicitly captured
          if not cond:
            raiseAssert "'$#'' failed: lhs: '$#', rhs: '$#'" % [s, $lhs, $rhs]
      let a = 3
      check2 a*2 == a+3
      if false: check2 a*2 < a+1 # would error with: 'a * 2 < a + 1'' failed: lhs: '6', rhs: '4'

  Example:

      # This example goes in more details about the capture semantics.
      macro fun(a: string, b: static bool): untyped =
        let c = 'z'
        var d = 11 # implicitly {.gensym.} and needs to be captured for use in `genAst`.
        proc localFun(): auto = 12 # implicitly {.inject.}, doesn't need to be captured.
        genAst(a, b, c = true):
          # `a`, `b` are captured explicitly, `c` is a local definition masking `c = 'z'`.
          const b2 = b # macro static param `b` is forwarded here as a static param.
          # `echo d` would give: `var not init` because `d` is not captured.
          (a & a, b, c, localFun()) # localFun can be called without capture.
      assert fun("ab", false) == ("abab", false, true, 12)

  Source Edit

# Templates

    template genAst(args: varargs[untyped]): untyped

  Convenience wrapper around `genAstOpt`. Source Edit