Expression Handling in JMP: Tips and Trapdoors

hogi — Fri, 14 Nov 2025 15:28:20 GMT

Collection of useful resources on the web:

There is a wonderful lecture by @joseph_morgan in the Discovery Summit Series:
https://community.jmp.com/t5/Abstracts/Using-JSL-to-Develop-Efficient-Robust-Applications-EU-2018-415/ev-p/849638
Joseph explains the secrets and possibilities of Expression Handling in JSL - and the trapdoors associated with the functionality.
The lecture is based on the content of
by @Jasean
(step-by-step guide through Universal Tricks #1 & #2, see below)
The Difference between Strings and Expressions - in 50 lines:
reply to a community post by @Craige_Hales
Nice Course with many application cases: Session 9: Advanced JSL , @jthi
further info can be found in the Scripting Guide: advanced-expressions-macros-and-lists

Basics
internal:
#062 - expression handling in JSL
#092 - expression handling

1	don't evaluate the expression (2+1), just store it in the variable x	x= Expr(2+1)
2	get the expression which is stored in x	Name Expr(x)
3	force evaluation	Eval(myexpr)
4	evaluate xyz and replace Expr(xyz) with the return value	Eval Expr( ... Expr(xyz))

*) NB: in 1 and 4, it's the same function "Expr(...)" - but with the opposite effect:
In 1, the content of Expr doesn't get evaluated, in 4 JUST the content of Expr gets evaluated

3 Universal Tricks

1	pre-evaluate parts of an expression via Eval Expr() ... then evaluate the expression via Eval() solves 90%, (with option 2: 99%) of all issues	Eval(Eval Expr ( ... Exp(eval 1st) ...)) option 2: Eval(Eval Expr ( ... Exp(Name Expr( )) ...))
2	Solves the same 99% like # 1 - option 2	Eval(substitute(Expr(), Expr(), Name Expr() ))
3	ultimate trick for column references ( @jthi, e.g. Session 9: Advanced JSL @33min )	Name Expr(as column("column name" or :column))

NB:
Some functions evaluate their arguments, some don't, some evaluate some of their arguments - there are functions like head() which evaluate their arguments to a certain degree: - and others evaluate their argument but if it's a single variable, they behave like Name Expr():

Unfortunately, most of these details are not available for the users. The users have to guess.

Here is a wish for JSL editor to help the users by showing this information interactively:

-> If you want to get this automatic support, please follow the link and vote!

Examples from the community:

Topic	Links	Details
Column() vs. As column() vs. name()		the universal syntax to reference a column is :column. But often, it's tricky to get the ":column" right ...
Column references in column formulas		define the column via `col = Name Expr(As Column(colname))` and insert it with Eval(Substitute()) Alternatives: As Column (Expr(colname)) with Eval(Eval Expr()) or Expr(Name Expr(AsColumn(dt, colname))) with Eval(Eval Expr()) ...
Column references in platform calls and messages		use `Name Expr(As Column(colname))` with Eval(substitute()) ... or if you have issues with a column list, just add eval() or evallist()in the column() argument
use a column reference in a function call		- wrap the column with Name Expr() - use a list
construct an expression		- start with an empty draft and fill it via insert into(draft, arguments) - use substitute - create a list, and substitute list with another JSL symbol
further workarounds via Expression handling		prevent inappropriate caching in Col Quantile by using an expression.
From version to version, less expression handling is needed to make things work	link?

[More Topic Containers like this]

Re: Expression Handling in JMP: Tipps and Trapdoors

SDF1 — Thu, 18 Apr 2024 14:59:54 GMT

Hi @hogi ,

Thanks for consolidating this information and bringing a lot of this information together. The talk sounds really informative.

I do like how you can do things several different ways in JMP and in JSL, but sometimes there are too many different ways that are very specific to the case at hand, and this can become somewhat cumbersome when trying to make code that is generic and able to handle many different scenarios.

Thanks!,

Re: Expression Handling in JMP: Tipps and Trapdoors

hogi — Tue, 03 Dec 2024 06:58:14 GMT

If you don't use the tricks:

Re: Expression Handling in JMP: Tipps and Trapdoors

hogi — Tue, 07 Jan 2025 20:12:54 GMT

JSL and variables - 3 issue you should be aware off when writing JSL code.

Different issues, always the same solution : )

the solution?

-> just read the main post.

c= 5;
col = Name Expr(:height);
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
gb = graph Builder(); framebox = report(gb)[FrameBox(1)];

 // issues with variables in a message
// all  3 of them look quite innocent 
// but none of them will survive a restart 

 New Column ("rescaled", Formula (c * :height)); 
 dt << New Column ("rescaled", Formula (5 * col));
 framebox << Add Graphics Script(Y Function( c * x, x ) );
 
 // no issue here:
 dt << concatenate(dt);
 dt << new column(c, formula(3));

One could think: don't ever use a variable in a message!
But this goes way too far - the last 2 examples don't have an issue.

topic Expression Handling in JMP: Tips and Trapdoors in Discussions

Expression Handling in JMP: Tips and Trapdoors

Re: Expression Handling in JMP: Tipps and Trapdoors

Re: Expression Handling in JMP: Tipps and Trapdoors

Re: Expression Handling in JMP: Tipps and Trapdoors