Preparser

The preparser provides a variety of convenience commands that simplify the process of writing model source code.

List of preparser commands

For loops

A for loop can be used to parameterize and repeat certain parts of the model source code.

Abbreviated syntax with implicit control name

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

Full syntax with explicit control name

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

If-then branches

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

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;
    ...