AST - transitional

# Syntax tree - transitional mode

This chapter presents the Camlp5 syntax tree when Camlp5 is installed in transitional mode.

## Introduction

This syntax tree is defined in the module "`MLast`" provided by Camlp5. Each node corresponds to a syntactic entity of the corresponding type.

For example, the syntax tree of the statement "`if`" can be written:

      MLast.ExIfe loc e1 e2 e3

where "`loc`" is the location in the source, and "`e1`", "`e2`" and "`e3`" are respectively the expression after the "`if`", the one after the "`then`" and the one after the "`else`".

If a program needs to manipulate syntax trees, it can use the nodes defined in the module "`MLast`". The programmer must know how the concrete syntax is transformed into this abstract syntax.

A simpler solution is to use one of the quotation kit "`q_MLast.cmo`". It proposes quotations which represent the abstract syntax (the nodes of the module "`MLast`") into concrete syntax with antiquotations to bind variables inside. The example above can be written:

      <:expr< if $e1$ then $e2$ else $e3$ >>

This representation is very interesting when one wants to manipulate complicated syntax trees. Here is an example taken from the Camlp5 sources themselves:

      <:expr<
        match try Some $f$ with [ Stream.Failure -> None ] with
        [ Some $p$ -> $e$
        | _ -> raise (Stream.Error $e2$) ]
      >>

This example was in a position of a pattern. In abstract syntax, it should have been written:

      MLast.ExMat _
        (MLast.ExTry _ (MLast.ExApp _ (MLast.ExUid _ "Some") f)
           [(MLast.PaAcc _ (MLast.PaUid _ "Stream") (MLast.PaUid _ "Failure"),
             None, MLast.ExUid _ "None")])
        [(MLast.PaApp _ (MLast.PaUid _ "Some") p, None, e);
         (MLast.PaAny _, None,
          MLast.ExApp _ (MLast.ExLid _ "raise")
            (MLast.ExApp _
               (MLast.ExAcc _ (MLast.ExUid _ "Stream") (MLast.ExUid _ "Error"))
               e2))]

Which is less readable and much more complicated to build and update.

Instead of thinking of "a syntax tree", the programmer can think of "a piece of program".

## Location

In all syntax tree nodes, the first parameter is the source location of the node.

### In expressions

When a quotation is in the context of an expression, the location parameter is "`loc`" in the node and in all its possible sub-nodes. Example: if we consider the quotation:

      <:sig_item< value foo : int -> bool >>

This quotation, in a context of an expression, is equivalent to:

      MLast.SgVal loc "foo"
        (MLast.TyArr loc (MLast.TyLid loc "int") (MLast.TyLid loc "bool"));

The name "`loc`" is predefined. However, it is possible to change it, using the argument "`-loc`" of the Camlp5 shell commands.

Consequently, if there is no variable "`loc`" defined in the context of the quotation, or if it is not of the correct type, a semantic error occur in the OCaml compiler ("Unbound value loc").

Note that in the extensible grammars, the variable "`loc`" is bound, in all semantic actions, to the location of the rule.

If the created node has no location, the programmer can define a variable named "`loc`" equal to "`Ploc.dummy`".

### In patterns

When a quotation is in the context of a pattern, the location parameter of all nodes and possible sub-nodes is set to the wildcard ("`_`"). The same example above:

      <:sig_item< value foo : int -> bool >>

is equivalent, in a pattern, to:

      MLast.SgVal _ "foo"
        (MLast.TyArr _ (MLast.TyLid _ "int") (MLast.TyLid _ "bool"))

However, it is possible to generate a binding of the variable "`loc`" on the top node by writing a "colon" before the "less" in the quotation. The same example:

      <:sig_item:< value foo : int -> bool >>

is equivalent to:

      MLast.SgVal loc "foo"
        (MLast.TyArr _ (MLast.TyLid _ "int") (MLast.TyLid _ "bool"))

## Antiquotations

The expressions or patterns between dollar ($) characters are called antiquotations. In opposition to quotations which has its own syntax rules, the antiquotation is an area in the syntax of the enclosing context (expression or pattern). See the chapter about quotations.

If a quotation is in the context of an expression, the antiquotation must be an expression. It can be any expression, including function calls. Examples:

      value f e el = <:expr< [$e$ :: $loop False el$] >>;
      value patt_list p pl = <:patt< ( $list:[p::pl]$) >>;

If a quotation is in the context of an pattern, the antiquotation is a pattern. Any pattern is possible, including the wildcard character ("`_`"). Examples:

       fun [ <:expr< $lid:op$ $_$ $_$ >> -> op ]
       match p with [ <:patt< $_$ | $_$ >> -> Some p ]

## Nodes and Quotations

This section describes all nodes defined in the module "MLast" of Camlp5 and how to write them with quotations. Notice that, inside quotations, one is not restricted to these elementary cases, but any complex value can be used, resulting on possibly complex combined nodes.

Variables names give information of their types:

- `e`, `e1`, `e2`, `e3`: expr
- `p`, `p1`, `p2`, `p3`: patt
- `t`, `t1`, `t2`, `e3`: ctyp
- `s`: string
- `b`: bool
- `me`, `me1`, `me2`: module_expr
- `mt`, `mt1`, `mt2`: module_type
- `le`: list expr
- `lp`: list patt
- `lt`: list ctyp
- `ls`: list string
- `lse`: list (string * expr)
- `lpe`: list (patt * expr)
- `lpp`: list (patt * patt)
- `lpee`: list (patt * option expr * expr)
- `op`: option patt
- `lcsi`: list class_str_item
- `lcsi`: list class_sig_item

### expr

Expressions of the language.

Node | `<:expr< ... >>` | Comment
--- | --- | ---
`ExAcc loc e1 e2` | `$e1$ . $e2$` | access
`ExAnt loc e` | `$anti:e$` | antiquotation (1)
`ExApp loc e1 e2` | `$e1$ $e2$` | application
`ExAre loc e1 e2` | `$e1$ .( $e2$ )` | array element
`ExArr loc le` | `[| $list:le$ |]` | array
`ExAsr loc e` | `assert $e$` | assert
`ExAss loc e1 e2` | `$e1$ := $e2$` | assignment
`ExBae loc e le` | `$e$ .{ $list:le$ }` | big array element
`ExChr loc s` | `$chr:s$` | character constant
`ExCoe loc e None t2` | `($e$ :> $t2$)` | coercion
`ExCoe loc e (Some t1) t2` | `($e$ : $t1$ :> $t2$)` | coercion
`ExFlo loc s` | `$flo:s$` | float constant
`ExFor loc s e1 e2 True le` | `for $lid:s$ = $e1$ to $e2$ do { $list:le$ }` | for (increasing)
`ExFor loc s e1 e2 False le` | `for $lid:s$ = $e1$ downto $e2$ do { $list:le$ }` | for (decreasing)
`ExFor loc s e1 e2 b le` | `for $lid:s$ = $e1$ $to:b$ $e2$ do { $list:le$ }` | for
`ExFun loc lpee` | `fun [ $list:lpee$ ]` | function (2)
`ExIfe loc e1 e2 e3` | `if $e1$ then $e2$ else $e3$` | if
`ExInt loc s1 ""` | `$int:s1$` | integer constant
`ExInt loc s1 "l"` | `$int32:s1$` | integer 32 bits
`ExInt loc s1 "L"` | `$int64:s1$` | integer 64 bits
`ExInt loc s1 "n"` | `$nativeint:s1$` | native integer
`ExLab loc p None` | `~{$p$}` | label
`ExLab loc p (Some e)` | `~{$p$ = $e$}` | label
`ExLab loc p oe` | `~{$p$ $opt:oe$}` | label
`ExLaz loc e` | `lazy $e$` | lazy
`ExLet loc True lpe e` | `let rec $list:lpe$ in $e$` | let rec
`ExLet loc False lpe e` | `let $list:lpe$ in $e$` | let not rec
`ExLet loc b lpe e` | `let $flag:b$ $list:lpe$ in $e$` | let
`ExLid loc s` | `$lid:s$` | lowercase identifier
`ExLmd loc s me e` | `let module $uid:s$ = $me$ in $e$` | let module
`ExMat loc e lpee` | `match $e$ with [ $list:lpee$ ]` | match (2)
`ExNew loc ls` | `new $list:ls$` | new
`ExObj loc None lcsi` | `object $list:lcsi$ end` | object expression
`ExObj loc (Some p) lcsi` | `object ($p$) $list:lcsi$ end` | object expression
`ExObj loc op lcsi` | `object $opt:op$ $list:lcsi$ end` | object expression
`ExOlb loc p None` | `?{$p$}` | option label
`ExOlb loc p (Some e)` | `?{$p$ = $e$}` | option label
`ExOlb loc p oe` | `?{$p$ $opt:oe$}` | option label
`ExOvr loc lse` | `{< $list:lse$ >}` | override
`ExPck loc me None` | `(module $me$)` | module packing
`ExPck loc me (Some mt)` | `(module $me$ : $mt$)` | module packing
`ExRec loc lpe None` | `{$list:lpe$}` | record
`ExRec loc lpe (Some e)` | `{($e$) with $list:lpe$}` | record
`ExSeq loc le` | `do { $list:le$ }` | sequence
`ExSnd loc e s` | `$e$ # $s$` | method call
`ExSte loc e1 e2` | `$e1$ .[ $e2$ ]` | string element
`ExStr loc s` | `$str:s$` | string
`ExTry loc e lpee` | `try $e$ with [ $list:lpee$ ]` | try (2)
`ExTup loc le` | `($list:le$)` | t-uple
`ExTyc loc e t` | `($e$ : $t$)` | type constraint
`ExUid loc s` | `$uid:s$` | uppercase identifier
`ExVrn loc s` | `` $s$` | variant
`ExWhi loc e le` | `while $e$ do { $list:le$ }` | while

(1)

Node used in the quotation expanders to tells at conversion to OCaml compiler syntax tree time, that all locations of the sub-tree is correcty located in the quotation. By default, in quotations, the locations of all generated nodes are the location of the whole quotation. This node allows to make an exception to this rule, since we know that the antiquotation belongs to the universe of the enclosing program. See the chapter about quotations and, in particular, its section about antiquotations.

(2)

The variable "lpee" found in "function", "match" and "try" statements correspond to a list of "`(patt * option expr * expr)`" where the "`option expr`" is the "when" optionally following the pattern:

      p -> e

is represented by:

      (p, None, e)

and

      p when e1 -> e

is represented by:

      (p, Some e1, e)

### patt

Patterns of the language.

Node | `<:patt< ... >>` | Comment
--- | --- | ---
`PaAcc loc p1 p2` | `$p1$ . $p2$` | access
`PaAli loc p1 p2` | `($p1$ as $p2$)` | alias
`PaAnt loc p` | `$anti:p$` | antiquotation (1)
`PaAny loc` | `_` | wildcard
`PaApp loc p1 p2` | `$p1$ $p2$` | application
`PaArr loc lp` | `[| $list:lp$ |]` | array
`PaChr loc s` | `$chr:s$` | character
`PaFlo loc s` | `$flo:s$` | float
`PaInt loc s1 ""` | `$int:s1$` | integer constant
`PaInt loc s1 "l"` | `$int32:s1$` | integer 32 bits
`PaInt loc s1 "L"` | `$int64:s1$` | integer 64 bits
`PaInt loc s1 "n"` | `$nativeint:s1$` | native integer
`PaLab loc p1 None` | `~{$p1$}` | label
`PaLab loc p1 (Some p2)` | `~{$p1$ = $p2$}` | label
`PaLab loc p1 op2` | `~{$p1$ $opt:op2$}` | label
`PaLaz loc p` | `lazy $p$` | lazy
`PaLid loc s` | `$lid:s$` | lowercase identifier
`PaNty loc s` | `(type $lid:s$)` | new type
`PaOlb loc p None` | `?{$p$}` | option label
`PaOlb loc p (Some e)` | `?{$p$ = $e$}` | option label
`PaOlb loc p oe` | `?{$p$ $opt:oe$}` | option label
`PaOrp loc p1 p2` | `$p1$ | $p2$` | or
`PaRec loc lpp` | `{ $list:lpp$ }` | record
`PaRng loc p1 p2` | `$p1$ .. $p2$` | range
`PaStr loc s` | `$str:s$` | string
`PaTup loc lp` | `($list:lp$)` | t-uple
`PaTyc loc p t` | `($p$ : $t$)` | type constraint
`PaTyp loc ls` | `# $list:ls$` | type pattern
`PaUid loc s` | `$uid:s$` | uppercase identifier
`PaUnp loc s None` | `(module $uid:s$)` | module unpacking
`PaUnp loc s (Some mt)` | `(module $uid:s$ : $mt$)` | module unpacking
`PaVrn loc s` | `` $s$` | variant

(1) Node used to specify an antiquotation area, like for the equivalent node in expressions. See above.

### ctyp

Type expressions of the language.

Node | `<:ctyp< ... >>` | Comment
--- | --- | ---
`TyAcc loc t1 t2` | `$t1$ . $t2$` | access
`TyAli loc t1 t2` | `$t1$ as $t2$` | alias
`TyAny loc` | `_` | wildcard
`TyApp loc t1 t2` | `$t1$ $t2$` | application
`TyArr loc t1 t2` | `$t1$ -> $t2$` | arrow
`TyCls loc ls` | `# $list:ls$` | class
`TyLab loc s t` | `~$s$: $t$` | label
`TyLid loc s` | `$lid:s$` | lowercase identifier
`TyMan loc t1 True t2` | `$t1$ == private $t2$` | manifest
`TyMan loc t1 False t2` | `$t1$ == $t2$` | manifest
`TyMan loc t1 b t2` | `$t1$ == $priv:b$ $t2$` | manifest
`TyObj loc lst True` | `< $list:lst$ .. >` | object
`TyObj loc lst False` | `< $list:lst$ >` | object
`TyObj loc lst b` | `< $list:lst$ $flag:b$ >` | object
`TyOlb loc s t` | `?$s$: $t$` | option label
`TyPck loc mt` | `(module $mt$)` | package
`TyPol loc ls t` | `! $list:ls$ . $t$` | polymorph
`TyQuo loc s` | `'$s$` | variable
`TyRec loc llsbt` | `{ $list:llsbt$ }` | record
`TySum loc llslt` | `[ $list:llslt$ ]` | sum
`TyTup loc lt` | `( $list:lt$ )` | t-uple
`TyUid loc s` | `$uid:s$` | uppercase identifier
`TyVrn loc lpv None` | `[ = $list:lpv$ ]` | variant
`TyVrn loc lpv (Some None)` | `[ > $list:lpv$ ]` | variant
`TyVrn loc lpv (Some (Some []))` | `[ < $list:lpv$ ]` | variant
`TyVrn loc lpv (Some (Some ls))` | `[ < $list:lpv$ > $list:ls$ ]` | variant

### modules...

#### str_item

Structure items, i.e. phrases in a ".ml" file or "struct" elements.

Node | `<:str_item< ... >>` | Comment
--- | --- | ---
`StCls loc lcice` | `class $list:lcice$` | class declaration
`StClt loc lcict` | `class type $list:lcict$` | class type declaration
`StDcl loc lsi` | `declare $list:lsi$ end` | declare
`StDir loc s None` | `# $lid:s$` | directive
`StDir loc s (Some e)` | `# $lid:s$ $e$` | directive
`StDir loc s oe` | `# $lid:s$ $opt:oe$` | directive
`StExc loc s [] []` | `exception $uid:s$` | exception
`StExc loc s lt []` | `exception $uid:s$ of $list:lt$` | exception
`StExc loc s [] ls` | `exception $uid:s$ = $list:ls$` | exception
`StExc loc s lt ls` | `exception $uid:s$ of $list:lt$ = $list:ls$` | exception
`StExp loc e` | `$exp:e$` | expression
`StExt loc s t ls` | `external $s$ : $t$ = $list:ls$` | external
`StInc loc me` | `include $me$` | include
`StMod loc True lsme` | `module rec $list:lsme$` | module rec
`StMod loc False lsme` | `module $list:lsme$` | module non rec
`StMod loc b lsme` | `module $flag:b$ $list:lsme$` | module
`StMty loc s mt` | `module type $s$ = $mt$` | module type
`StOpn loc ls` | `open $list:ls$` | open
`StTyp loc ltd` | `type $list:ltd$` | type declaration
`StUse loc s lsil` | `# $str:s$ $list:lsil$` | ... internal use ... (1)
`StVal loc True lpe` | `value rec $list:lpe$` | value rec
`StVal loc False lpe` | `value $list:lpe$` | value non rec
`StVal loc b lpe` | `value $flag:b$ $list:lpe$` | value

(1)

Node internally used to specify a different file name applying to the whole subtree. This is generated by the directive "use" and used when converting to the OCaml syntax tree which needs the file name in its location type.

#### sig_item

Signature items, i.e. phrases in a ".mli" file or elements inside "sig ... end".

Node | `<:sig_item< ... >>` | Comment
--- | --- | ---
`SgCls loc lcict` | `class $list:lcict$` | class
`SgClt loc lcict` | `class type $list:lcict$` | class type
`SgDcl loc lsi` | `declare $list:lsi$ end` | declare
`SgDir loc s None` | `# $lid:s$` | directive
`SgDir loc s (Some e)` | `# $lid:s$ $e$` | directive
`SgDir loc s oe` | `# $lid:s$ $opt:oe$` | directive
`SgExc loc s []` | `exception $s$` | exception
`SgExc loc s lt` | `exception $s$ of $list:lt$` | exception
`SgExt loc s t ls` | `external $s$ : $t$ = $list:ls$` | external
`SgInc loc mt` | `include $mt$` | include
`SgMod loc True lsmt` | `module rec $list:lsmt$` | module rec
`SgMod loc False lsmt` | `module $list:lsmt$` | module non rec
`SgMod loc b lsmt` | `module $flag:b$ $list:lsmt$` | module
`SgMty loc s mt` | `module type $s$ = $mt$` | module type
`SgOpn loc ls` | `open $list:ls$` | open
`SgTyp loc ltd` | `type $list:ltd$` | type declaration
`SgUse loc s lsil` | `# $str:s$ $list:lsil$` | ... internal use ... (1)
`SgVal loc s t` | `value $s$ : $t$` | value

(1)

Same remark as for "`str_item`" above.

#### module_expr

Node | `<:module_expr< ... >>` | Comment
--- | --- | ---
`MeAcc loc me1 me2` | `$me1$ . $me2$` | access
`MeApp loc me1 me2` | `$me1$ $me2$` | application
`MeFun loc s mt me` | `functor ($s$ : $mt$) -> $me$` | functor
`MeStr loc lsi` | `struct $list:lsi$ end` | struct
`MeTyc loc me mt` | `($me$ : $mt$)` | module type constraint
`MeUid loc s` | `$uid:s$` | uppercase identifier
`MeUnp loc e None` | `(value $e$)` | module unpacking
`MeUnp loc e (Some mt)` | `(value $e$ : $mt$)` | module unpacking

#### module_type

Node | `<:module_type< ... >>` | Comment
--- | --- | ---
`MtAcc loc mt1 mt2` | `$mt1$ . $mt2$` | access
`MtApp loc mt1 mt2` | `$mt1$ $mt2$` | application
`MtFun loc s mt1 mt2` | `functor ($s$ : $mt1$) -> $mt2$` | functor
`MtLid loc s` | `$lid:s$` | lowercase identifier
`MtQuo loc s` | `' $s$` | abstract
`MtSig loc lsi` | `sig $list:lsi$ end` | signature
`MtTyo loc me` | `module type of $me$` | of module expression
`MtUid loc s` | `$uid:s$` | uppercase identifier
`MtWit loc mt lwc` | `$mt$ with $list:lwc$` | with construction

### classes...

#### class_expr

Node | `<:class_expr< ... >>` | Comment
--- | --- | ---
`CeApp loc ce e` | `$ce$ $e$` | application
`CeCon loc ls lt` | `[ $list:lt$ ] $list:ls$` | constructor
`CeFun loc p ce` | `fun $p$ -> $ce$` | function
`CeLet loc True lpe ce` | `let rec $list:lpe$ in $ce$` | let rec
`CeLet loc False lpe ce` | `let $list:lpe$ in $ce$` | let non rec
`CeLet loc b lpe ce` | `let $flag:b$ $list:lpe$ in $ce$` | let
`CeStr loc None lcsi` | `object $list:lcsi$ end` | object
`CeStr loc (Some p) lcsi` | `object ($p$) $list:lcsi$ end` | object
`CeStr loc op lcsi` | `object $opt:op$ $list:lcsi$ end` | object
`CeTyc loc ce ct` | `($ce$ : $ct$)` | class type constraint

#### class_type

Node | `<:class_type< ... >>` | Comment
--- | --- | ---
`CtAcc loc ct1 ct2` | `$ct1$ . $ct2$` | access
`CtApp loc ct1 ct2` | `$ct1$ $ct2$` | application
`CtCon loc ct lt` | `$ct$ [ $list:lt$ ]` | constructor
`CtFun loc t ct` | `[ $t$ ] -> $ct$` | arrow
`CtIde loc s` | `$id:s$` | identifier
`CtSig loc None lcsi` | `object $list:lcsi$ end` | object
`CtSig loc (Some t) lcsi` | `object ($t$) $list:lcsi$ end` | object
`CtSig loc ot lcsi` | `object $opt:ot$ $list:lcsi$ end` | object

#### class_str_item

Node | `<:class_str_item< ... >>` | Comment
--- | --- | ---
`CrCtr loc t1 t2` | `type $t1$ = $t2$` | type constraint
`CrDcl loc lcsi` | `declare $list:lcsi$ end` | declaration list
`CrInh loc ce None` | `inherit $ce$` | inheritance
`CrInh loc ce (Some s)` | `inherit $ce$ $opt:Some s$` | inheritance
`CrInh loc ce os` | `inherit $ce$ $opt:os$` | inheritance
`CrIni loc e` | `initializer $e$` | initialization
`CrMth loc True True s None e` | `method! private $lid:s$ = $e$` | method
`CrMth loc True True s (Some t) e` | `method! private $lid:s$ : $t$ = $e$` | method
`CrMth loc True True s ot e` | `method! private $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc True False s None e` | `method! $lid:s$ = $e$` | method
`CrMth loc True False s (Some t) e` | `method! $lid:s$ : $t$ = $e$` | method
`CrMth loc True False s ot e` | `method! $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc True b2 s None e` | `method! $priv:b2$ $lid:s$ = $e$` | method
`CrMth loc True b2 s (Some t) e` | `method! $priv:b2$ $lid:s$ : $t$ = $e$` | method
`CrMth loc True b2 s ot e` | `method! $priv:b2$ $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc False True s None e` | `method private $lid:s$ = $e$` | method
`CrMth loc False True s (Some t) e` | `method private $lid:s$ : $t$ = $e$` | method
`CrMth loc False True s ot e` | `method private $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc False False s None e` | `method $lid:s$ = $e$` | method
`CrMth loc False False s (Some t) e` | `method $lid:s$ : $t$ = $e$` | method
`CrMth loc False False s ot e` | `method $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc False b2 s None e` | `method $priv:b2$ $lid:s$ = $e$` | method
`CrMth loc False b2 s (Some t) e` | `method $priv:b2$ $lid:s$ : $t$ = $e$` | method
`CrMth loc False b2 s ot e` | `method $priv:b2$ $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc b1 True s None e` | `method $!:b1$ private $lid:s$ = $e$` | method
`CrMth loc b1 True s (Some t) e` | `method $!:b1$ private $lid:s$ : $t$ = $e$` | method
`CrMth loc b1 True s ot e` | `method $!:b1$ private $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc b1 False s None e` | `method $!:b1$ $lid:s$ = $e$` | method
`CrMth loc b1 False s (Some t) e` | `method $!:b1$ $lid:s$ : $t$ = $e$` | method
`CrMth loc b1 False s ot e` | `method $!:b1$ $lid:s$ $opt:ot$ = $e$` | method
`CrMth loc b1 b2 s None e` | `method $!:b1$ $priv:b2$ $lid:s$ = $e$` | method
`CrMth loc b1 b2 s (Some t) e` | `method $!:b1$ $priv:b2$ $lid:s$ : $t$ = $e$` | method
`CrMth loc b1 b2 s ot e` | `method $!:b1$ $priv:b2$ $lid:s$ $opt:ot$ = $e$` | method
`CrVal loc True True s e` | `value! mutable $lid:s$ = $e$` | value
`CrVal loc True False s e` | `value! $lid:s$ = $e$` | value
`CrVal loc True b2 s e` | `value! $flag:b2$ $lid:s$ = $e$` | value
`CrVal loc False True s e` | `value mutable $lid:s$ = $e$` | value
`CrVal loc False False s e` | `value $lid:s$ = $e$` | value
`CrVal loc False b2 s e` | `value $flag:b2$ $lid:s$ = $e$` | value
`CrVal loc b1 True s e` | `value $!:b1$ mutable $lid:s$ = $e$` | value
`CrVal loc b1 False s e` | `value $!:b1$ $lid:s$ = $e$` | value
`CrVal loc b1 b2 s e` | `value $!:b1$ $flag:b2$ $lid:s$ = $e$` | value
`CrVav loc True s t` | `value virtual mutable $lid:s$ : $t$` | virtual value
`CrVav loc False s t` | `value virtual $lid:s$ : $t$` | virtual value
`CrVav loc b s t` | `value virtual $flag:b$ $lid:s$ : $t$` | virtual value
`CrVir loc True s t` | `method virtual private $lid:s$ : $t$` | virtual method
`CrVir loc False s t` | `method virtual $lid:s$ : $t$` | virtual method
`CrVir loc b s t` | `method virtual $flag:b$ $lid:s$ : $t$` | virtual method

#### class_sig_item

Node | `<:class_sig_item< ... >>` | Comment
--- | --- | ---
`CgCtr loc t1 t2` | `type $t1$ = $t2$` | type constraint
`CgDcl loc lcsi` | `declare $list:lcsi$ end` | declare
`CgInh loc ct` | `inherit $ct$` | inheritance
`CgMth loc True s t` | `method private $lid:s$ : $t$` | method
`CgMth loc False s t` | `method $lid:s$ : $t$` | method
`CgMth loc b s t` | `method $flag:b$ $lid:s$ : $t$` | method
`CgVal loc True s t` | `value mutable $lid:s$ : $t$` | value
`CgVal loc False s t` | `value $lid:s$ : $t$` | value
`CgVal loc b s t` | `value $flag:b$ $lid:s$ : $t$` | value
`CgVir loc True s t` | `method virtual private $lid:s$ : $t$` | virtual method
`CgVir loc False s t` | `method virtual $lid:s$ : $t$` | virtual method
`CgVir loc b s t` | `method virtual $flag:b$ $lid:s$ : $t$` | virtual method

### other

#### type_decl

What is after 'type' or 'and' in a type declaration.

Node | `<:type_decl< ... >>`
--- | ---
`{tdNam=ls;tdPrm=ltv;tdPrv=True;tdDef=t;tdCon=ltt}` | `$tp:ls$ $list:ltv$ = private $t$ $list:ltt$`
`{tdNam=ls;tdPrm=ltv;tdPrv=False;tdDef=t;tdCon=ltt}` | `$tp:ls$ $list:ltv$ = $t$ $list:ltt$`
`{tdNam=ls;tdPrm=ltv;tdPrv=b;tdDef=t;tdCon=ltt}` | `$tp:ls$ $list:ltv$ = $priv:b$ $t$ $list:ltt$`

#### with_constr

"With" possibly following a module type.

Node | `<:with_constr< ... >>` | Comment
--- | --- | ---
`WcMod loc ls me` | `module $list:ls$ = $me$` | with module
`WcMos loc ls me` | `module $list:ls$ := $me$` | with module substitution
`WcTyp loc ls ltv True t` | `type $list:ls$ $list:ltv$ = private $t$` | with type
`WcTyp loc ls ltv False t` | `type $list:ls$ $list:ltv$ = $t$` | with type
`WcTyp loc ls ltv b t` | `type $list:ls$ $list:ltv$ = $flag:b$ $t$` | with type
`WcTys loc ls ltv t` | `type $list:ls$ $list:ltv$ := $t$` | with type substitution

#### poly_variant

Polymorphic variants.

Node | `<:poly_variant< ... >>` | Comment
--- | --- | ---
`PvTag loc s True []` | ``$s$` | constructor
`PvTag loc s True lt` | ``$s$ of & $list:lt$` | constructor
`PvTag loc s False lt` | ``$s$ of $list:lt$` | constructor
`PvTag loc s b lt` | ``$s$ of $flag:b$ $list:lt$` | constructor
`PvInh loc t` | `$t$` | type