jsonparse

declarations
 afct:array(range) of string
  s_ctx=record
   cnt:integer
  end-record
  c:s_ctx
end-declarations

public function setvalue_all(ctx:s_ctx,name:text,type:integer,val:text):integer
 if name="name" or name="age" then
  writeln(name,":",val)
  ctx.cnt+=1
 end-if
end-function

afct(JSON_FCT_TEXT):="setvalue_all"   ! A value as a text
fopen("mydoc.json",F_INPUT)
rts:=jsonparse(afct,c)
fclose(F_INPUT)
writeln("line count:",c.cnt)

1. This function is an alternative approach to jsonload for processing JSON documents: instead of loading into memory the entire document this function calls a dedicated routine whenever it identifies a JSON entity. For instance a specific function is called when an object is open and another one when it is closed. It is up to the Mosel program to decide how to handle the document via these event handling functions.

2. To each event type corresponds a specific function signature. These functions return an integer that decides whether parsing should continue: a non-zero value will cause the parsing to cancel (this value is used as the return value of jsonparse). The expected function signatures are:

JSON_FCT_OPEN_OBJ

function open_object(ctx:ctxtype, name:text):integer

JSON_FCT_CLOSE_OBJ

function close_object(ctx:ctxtype):integer

JSON_FCT_OPEN_ARR

function open_array(ctx:ctxtype, name:text):integer

JSON_FCT_CLOSE_ARR

function close_array(ctx:ctxtype):integer

JSON_FCT_TEXT

function text_val(ctx:ctxtype, name:text, type:integer, val:text):integer

JSON_FCT_NUM

function num_val(ctx:ctxtype, name:text, val:real):integer

JSON_FCT_BOOL

function bool_val(ctx:ctxtype, name:text, val:boolean):integer

JSON_FCT_NULL

function null_val(ctx:ctxtype, name:text):integer

In addition to the pre-defined arguments these functions take a context as their first parameter. This variable (that can be of any type) is provided to the jsonparse routine and can be used by the event functions for storing progress information.
The name argument is not empty only when the value corresponds to an object member: in this case this parameter is the label of this member. The type argument passed to the text_val function indicates the type of the data (0 for null, 1 for text, 2 for numerical and 3 for Boolean): this function is used with the textual representation of the value when the required type-specific function is not available. For instance this function will be called with type=3 if a Boolean value has been read and the entry JSON_FCT_BOOL is not defined in the function table.

3. An error message indicating the location of the error is displayed when the parsing fails or if an event function returns a negative value (a positive value also interrupts parsing but no message is displayed).