Preparser and pseudofunctions

The preparser provides a variety of convenience commands that simplify the process of writing model source code. Pseudofunctions provide a compact notation for frequently used temporal transformations. The preparser commands and pseudofunctions are processed before the model source code is parsed. The preparser commands and pseudofunctions can be used in both Simultaneous and Sequential models.

List of preparser commands

Command	Description
`!for ... !do ... !end`	For loops
`!if ... !then ... !else ... !end`	If-then-else branches
`!list(...)`	Lists
`# ...`	Line comments
`#{ ... #}`	Block comments

For loops

A for loop can be used to parameterize and repeat certain parts of the model source code. For loops can be nested. The loop body is delimited by the !do and !end keywords. The loop iterates over a list of tokens, assigning each token in turn to a control name. The control name can be implicit (the literal ?) or explicit (a name starting with a ? sign). If the control name is explicit, it can be parenthesized (the name is enclosed in parentheses) or not. The loop body can contain occurrences of the control name, which are replaced by the currently assigned token from the list.

Abbreviated syntax with implicit control name

!for a, b, c !do
    ...
!end

Any occurrence of the literal ? in the loop body is replaced by the currently assigned token from the list a, b, c.

Full syntax with explicit control name

!for ?name = a, b, c !do
    ...
!end

Any occurrence of the literal ?name in the loop body is replaced by the currently assigned token from the list a, b, c.

Full syntax with parenthesized explicit control name

!for ?(name) = a, b, c !do
    ...
!end

Any occurrence of the literal ?(name) in the loop body is replaced by the currently assigned token from the list a, b, c.

Any occurrence of ?{name} in the loop body is replaced by the uppercased token currently assigned to ?(name).

Any occurrence of ?{name} in the loop body is replaced by the lowercased token currently assigned to ?(name).

If-then-else branches

The if-then-else command can be used to conditionally include or exclude parts of the model source code.

!if condition !then
    ...
!else
    ...
!end

Lists

abc`n
def`n
ghi`x

...

!list(`n)
!list(`x)

The list command expands to the comma-separated list of all tokens (names) that were tagged a backtick followed by the name of the list. In the example above, the command !list(n)expands toabc, def, and the command!list(x) expands to ghi.

Comments

Comments can be either line comments (from a line comment sign, #, until the end of the line) or block comments (from an opening sign, #{, until the closing sign, #})

Line comments

# This is a line comment

Block comments

#{ This is a block ...
...comment
#}

Pseudofunctions

Pseudofunctions offer a compact notation for frequently used temporal transformations. The pseudofunctions are replaced by a literal text representation of the corresponding expression, for instance

diff(x + y)

is replaced by

((x + y) - (x[-1] + y[-1]))

Pseudofunction	Description	`Simultaneous`	`Sequential`
`diff`	Expands to first difference
`diff_log`	Expands to first difference of logarithms
`roc`	Expands to gross rate of change
`pct`	Expands to percent change
`mov_sum`	Expands to moving sum
`mov_avg`	Expands to moving average
`mov_prod`	Expands to moving product

Each pseudofunction can take one optional parameter, a time lag with a specific meaning. These parameters must be non-zero negative values.

Pseudofunction	Default parameter	Meaning
`diff`	`-1`	Number of periods over which the first difference is calculated
`diff_log`	`-1`	Number of periods over which the first difference of logarithms is calculated
`roc`	`-1`	Number of periods over which the rate of change is calculated
`pct`	`-1`	Number of periods over which the percent change is calculated
`mov_sum`	`-4`	Number of periods in the moving window, including the current period
`mov_avg`	`-4`	Number of periods in the moving window, including the current period
`mov_prod`	`-4`	Number of periods in the moving window, including the current period

Substitutions

!substitutions

    name1 := expression1;
    name2 := expression2;
    ...