version0.7.10
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Andreas Rumpf
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572
doc/astspec.txt
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572
doc/astspec.txt
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The AST in Nimrod
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=================
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This section describes how the AST is modelled with Nimrod's type system.
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The AST consists of nodes (``PNimrodNode``) with a variable number of
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children. Each node has a field named ``kind`` which describes what the node
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contains:
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.. code-block:: nimrod
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type
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TNimrodNodeKind = enum ## kind of a node; only explanatory
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nnkNone, ## invalid node kind
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nnkEmpty, ## empty node
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nnkIdent, ## node contains an identifier
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nnkIntLit, ## node contains an int literal (example: 10)
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nnkStrLit, ## node contains a string literal (example: "abc")
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nnkNilLit, ## node contains a nil literal (example: nil)
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nnkCaseStmt, ## node represents a case statement
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... ## many more
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PNimrodNode = ref TNimrodNode
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TNimrodNode {.final.} = object
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case kind ## the node's kind
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of nnkNone, nnkEmpty, nnkNilLit:
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nil ## node contains no additional fields
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of nnkCharLit..nnkInt64Lit:
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intVal: biggestInt ## the int literal
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of nnkFloatLit..nnkFloat64Lit:
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floatVal: biggestFloat ## the float literal
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of nnkStrLit..nnkTripleStrLit:
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strVal: string ## the string literal
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of nnkIdent:
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ident: TNimrodIdent ## the identifier
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of nnkSym:
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symbol: PNimrodSymbol ## the symbol (after symbol lookup phase)
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else:
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sons: seq[PNimrodNode] ## the node's sons (or children)
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For the ``PNimrodNode`` type, the ``[]`` operator has been overloaded:
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``n[i]`` is ``n``'s ``i``-th child.
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To specify the AST for the different Nimrod constructs, the notation
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``nodekind(son1, son2, ...)`` or ``nodekind(value)`` or
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``nodekind(field=value)`` is used.
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Leaf nodes/Atoms
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================
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A leaf of the AST often corresponds to a terminal symbol in the concrete
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syntax.
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----------------- ---------------------------------------------
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Nimrod expression corresponding AST
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----------------- ---------------------------------------------
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``42`` ``nnkIntLit(intVal = 42)``
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``42'i8`` ``nnkInt8Lit(intVal = 42)``
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``42'i16`` ``nnkInt16Lit(intVal = 42)``
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``42'i32`` ``nnkInt32Lit(intVal = 42)``
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``42'i64`` ``nnkInt64Lit(intVal = 42)``
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``42.0`` ``nnkFloatLit(floatVal = 42.0)``
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``42.0'f32`` ``nnkFloat32Lit(floatVal = 42.0)``
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``42.0'f64`` ``nnkFloat64Lit(floatVal = 42.0)``
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``"abc"`` ``nnkStrLit(strVal = "abc")``
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``r"abc"`` ``nnkRStrLit(strVal = "abc")``
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``"""abc"""`` ``nnkTripleStrLit(strVal = "abc")``
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``' '`` ``nnkCharLit(intVal = 32)``
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``nil`` ``nnkNilLit()``
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``myIdentifier`` ``nnkIdent(ident = !"myIdentifier")``
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``myIdentifier`` after lookup pass: ``nnkSym(symbol = ...)``
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----------------- ---------------------------------------------
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Identifiers are ``nnkIdent`` nodes. After the name lookup pass these nodes
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get transferred into ``nnkSym`` nodes. However, a macro receives an AST that
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has not been checked for semantics and thus the identifiers have not been
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looked up. Thus macros deal with ``nnkIdent`` nodes.
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Calls/expressions
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=================
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Command call
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------------
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Concrete syntax:
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.. code-block:: nimrod
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echo "abc", "xyz"
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AST:
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.. code-block:: nimrod
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nnkCommand(nnkIdent(!"echo"), nnkStrLit("abc"), nnkStrLit("xyz"))
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Call with ``()``
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----------------
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Concrete syntax:
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.. code-block:: nimrod
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echo("abc", "xyz")
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AST:
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.. code-block:: nimrod
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nnkCall(nnkIdent(!"echo"), nnkStrLit("abc"), nnkStrLit("xyz"))
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Infix operator call
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-------------------
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Concrete syntax:
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.. code-block:: nimrod
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"abc" & "xyz"
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AST:
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.. code-block:: nimrod
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nnkInfix(nnkIdent(!"&"), nnkStrLit("abc"), nnkStrLit("xyz"))
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Prefix operator call
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--------------------
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Concrete syntax:
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.. code-block:: nimrod
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? "xyz"
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AST:
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.. code-block:: nimrod
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nnkPrefix(nnkIdent(!"?"), nnkStrLit("abc"))
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Postfix operator call
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---------------------
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**Note:** There are no postfix operators in Nimrod. However, the
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``nnkPostfix`` node is used for the *asterisk export marker* ``*``:
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Concrete syntax:
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.. code-block:: nimrod
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identifier*
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AST:
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.. code-block:: nimrod
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nnkPostfix(nnkIdent(!"*"), nnkIdent(!"identifier"))
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Call with named arguments
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-------------------------
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Concrete syntax:
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.. code-block:: nimrod
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writeln(file=stdout, "hallo")
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AST:
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.. code-block:: nimrod
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nnkCall(nnkIdent(!"writeln"),
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nnkExprEqExpr(nnkIdent(!"file"), nnkIdent(!"stdout")),
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nnkStrLit("hallo"))
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Dereference operator ``^``
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--------------------------
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Concrete syntax:
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.. code-block:: nimrod
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x^
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AST:
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.. code-block:: nimrod
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nnkDerefExpr(nnkIdent(!"x"))
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Addr operator
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-------------
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Concrete syntax:
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.. code-block:: nimrod
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addr(x)
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AST:
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.. code-block:: nimrod
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nnkAddr(nnkIdent(!"x"))
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Cast operator
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-------------
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Concrete syntax:
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.. code-block:: nimrod
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cast[T](x)
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AST:
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.. code-block:: nimrod
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nnkCast(nnkIdent(!"T"), nnkIdent(!"x"))
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Object access operator ``.``
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----------------------------
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Concrete syntax:
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.. code-block:: nimrod
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x.y
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AST:
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.. code-block:: nimrod
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nnkDotExpr(nnkIdent(!"x"), nnkIdent(!"y"))
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Array access operator ``[]``
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----------------------------
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Concrete syntax:
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.. code-block:: nimrod
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x[y]
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AST:
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.. code-block:: nimrod
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nnkBracketExpr(nnkIdent(!"x"), nnkIdent(!"y"))
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Parentheses
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-----------
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Parentheses for affecting operator precedence or tuple construction
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are built with the ``nnkPar`` node.
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Concrete syntax:
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.. code-block:: nimrod
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(1, 2, (3))
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AST:
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.. code-block:: nimrod
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nnkPar(nnkIntLit(1), nnkIntLit(2), nnkPar(nnkIntLit(3)))
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Curly braces
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------------
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Curly braces are used as the set constructor.
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Concrete syntax:
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.. code-block:: nimrod
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{1, 2, 3}
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AST:
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.. code-block:: nimrod
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nnkCurly(nnkIntLit(1), nnkIntLit(2), nnkIntLit(3))
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Brackets
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--------
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Brackets are used as the array constructor.
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Concrete syntax:
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.. code-block:: nimrod
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[1, 2, 3]
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AST:
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.. code-block:: nimrod
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nnkBracket(nnkIntLit(1), nnkIntLit(2), nnkIntLit(3))
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Ranges
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------
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Ranges occur in set constructors, case statement branches or array slices.
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Concrete syntax:
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.. code-block:: nimrod
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1..3
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AST:
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.. code-block:: nimrod
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nnkRange(nnkIntLit(1), nnkIntLit(3))
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If expression
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-------------
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The representation of the if expression is subtle, but easy to traverse.
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Concrete syntax:
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.. code-block:: nimrod
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if cond1: expr1 elif cond2: expr2 else: expr3
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AST:
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.. code-block:: nimrod
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nnkIfExpr(
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nnkElifExpr(cond1, expr1),
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nnkElifExpr(cond2, expr2),
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nnkElseExpr(expr3)
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)
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Statements
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==========
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If statement
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------------
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The representation of the if statement is subtle, but easy to traverse. If
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there is no ``else`` branch, no ``nnkElse`` child exists.
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Concrete syntax:
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.. code-block:: nimrod
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if cond1:
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stmt1
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elif cond2:
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stmt2
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elif cond3:
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stmt3
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else:
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stmt4
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AST:
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.. code-block:: nimrod
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nnkIfStmt(
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nnkElifBranch(cond1, stmt1),
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nnkElifBranch(cond2, stmt2),
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nnkElifBranch(cond3, stmt3),
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nnkElse(stmt4)
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)
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When statement
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--------------
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Like the ``if`` statement, but the root has the kind ``nnkWhenStmt``.
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Assignment
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----------
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Concrete syntax:
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.. code-block:: nimrod
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x = 42
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AST:
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.. code-block:: nimrod
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nnkAsgn(nnkIdent(!"x"), nnkIntLit(42))
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Statement list
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--------------
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Concrete syntax:
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.. code-block:: nimrod
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stmt1
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stmt2
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stmt3
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AST:
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.. code-block:: nimrod
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nnkStmtList(stmt1, stmt2, stmt3)
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Case statement
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--------------
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Concrete syntax:
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.. code-block:: nimrod
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case expr1
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of expr2, expr3..expr4:
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stmt1
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of expr5:
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stmt2
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elif cond1:
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stmt3
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else:
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stmt4
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AST:
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.. code-block:: nimrod
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nnkCaseStmt(
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expr1,
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nnkOfBranch(expr2, nnkRange(expr3, expr4), stmt1),
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nnkOfBranch(expr5, stmt2),
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nnkElifBranch(cond1, stmt3),
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nnkElse(stmt4)
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)
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The ``nnkElifBranch`` and ``nnkElse`` parts may be missing.
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While statement
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---------------
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Concrete syntax:
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.. code-block:: nimrod
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while expr1:
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stmt1
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AST:
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.. code-block:: nimrod
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nnkWhileStmt(expr1, stmt1)
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For statement
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-------------
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Concrete syntax:
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.. code-block:: nimrod
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for ident1, ident2 in expr1:
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stmt1
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AST:
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.. code-block:: nimrod
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nnkForStmt(ident1, ident2, expr1, stmt1)
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Try statement
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-------------
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Concrete syntax:
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.. code-block:: nimrod
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try:
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stmt1
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except e1, e2:
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stmt2
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except e3:
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stmt3
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except:
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stmt4
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finally:
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stmt5
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AST:
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.. code-block:: nimrod
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nnkTryStmt(
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stmt1,
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nnkExceptBranch(e1, e2, stmt2),
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nnkExceptBranch(e3, stmt3),
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nnkExceptBranch(stmt4),
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nnkFinally(stmt5)
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)
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Return statement
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----------------
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Concrete syntax:
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.. code-block:: nimrod
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return expr1
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AST:
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.. code-block:: nimrod
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nnkReturnStmt(expr1)
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Yield statement
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---------------
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Like ``return``, but with ``nnkYieldStmt`` kind.
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Discard statement
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-----------------
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Like ``return``, but with ``nnkDiscardStmt`` kind.
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Continue statement
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------------------
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Concrete syntax:
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.. code-block:: nimrod
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continue
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AST:
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.. code-block:: nimrod
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nnkContinueStmt()
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Var section
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-----------
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To be written.
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Const section
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-------------
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To be written.
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Type section
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------------
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To be written.
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Procedure declaration
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---------------------
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To be written.
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Iterator declaration
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--------------------
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To be written.
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Template declaration
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--------------------
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To be written.
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Macro declaration
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-----------------
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To be written.
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Special node kinds
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==================
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There are several node kinds that are used for semantic checking or code
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generation. These are accessible from this module, but should not be used.
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Other node kinds are especially designed to make AST manipulations easier.
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These are explained here.
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To be written.
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