MakeExpression

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`MakeExpression`

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MakeExpression[boxes,form]

is the low‐level function used in Wolfram System sessions to construct expressions from boxes.

Details

MakeExpression returns its result wrapped in HoldComplete.
form can be StandardForm, TraditionalForm, or other forms for which interpretation rules have been defined.
You can give definitions for MakeExpression[expr,form] to specify your own rules for how boxes should be converted to expressions.
MakeExpression is not automatically called on the results it generates. This means that explicit MakeExpression calls must typically be inserted into definitions for MakeExpression.
MakeExpression is used whenever boxes are supplied as input to the Wolfram Language.
The boxes that are fed to MakeExpression are constructed from textual input by forming tokens, then grouping these according to standard Wolfram Language operator precedence rules, stripping out spacing characters. StyleBox and other objects not intended for interpretation are removed. »
Definitions you give for MakeExpression will override built‐in Wolfram Language rules for processing input.
Giving input prefaced by \! makes the Wolfram Language effectively perform MakeExpression.

Examples

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Basic Examples (1)Summary of the most common use cases

Convert boxes to an expression using StandardForm rules:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-j53

Out[1]=1

Scope (2)Survey of the scope of standard use cases

Convert boxes to an expression using TraditionalForm rules:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-dnh2f7

Out[1]=1

Convert the same boxes using StandardForm rules:

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-bu3d7v

Out[2]=2

The display of a box structure with style information:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-bv187c

MakeExpression removes the style information:

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-iht0kg

Out[2]=2

Properties & Relations (2)Properties of the function, and connections to other functions

MakeExpression does not evaluate the expression, while ToExpression does:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-j9yqkw

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-v65hi

Out[2]=2

Display an InterpretationBox:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-b4ov11

The expression is the second argument of the InterpretationBox:

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-j6ylmq

Out[2]=2

Possible Issues (2)Common pitfalls and unexpected behavior

Input containing invalid or incomplete syntax results in ErrorBox expressions:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-nlhpf9

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-b8h6om

Out[2]=2

The presence of some whitespace can prevent MakeExpression from interpreting a box structure:

In[1]:=1

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https://wolfram.com/xid/0i1kcipoy-ekuyxu

Out[1]=1

Use StripBoxes to strip whitespace and other boxes that interfere with interpretation:

In[2]:=2

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https://wolfram.com/xid/0i1kcipoy-e6mg28

Out[2]=2

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