TypeOf

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`TypeOf`

[Experimental]

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TypeOf[expr]

gives the type of expr without evaluating it.

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TypeOf[expr,Typed[x,ty]]

assumes that instances of x in expr have type ty.

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TypeOf[expr,{Typed[x₁,ty₁],Typed[x₂,ty₂],…}]

assumes that x_i has type ty_i.

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TypeOf[expr,decls]

uses declarations decls.

Details and Options

TypeOf can be used in both interpreted and compiled programs.
TypeOf uses the type inferencing system of the Wolfram Compiler.
TypeOf only accepts expressions and types that can be compiled by the Wolfram Compiler.
TypeOf can be used in interpreted code as a quick check whether compilation will work.
TypeOf can be used in compiled code to determine the type of some part of the code.
TypeOf can be used with TypeEvaluate to direct the type for a function declaration.
TypeOf can take both Typed and declaration specifications such as FunctionDeclaration and TypeDeclaration.

Examples

open allclose all

Basic Examples (6)Summary of the most common use cases

Find the type of a function::

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-txivdd

Out[1]=1

TypeOf is useful since it just determines the type of a function, giving an indication that compilation may work.

Find the type of an expression:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-kegnam

Out[1]=1

Find the type of an expression while specifying only the type of a subexpression:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-wsqcjn

Out[1]=1

Find the type of a function using a FunctionDeclaration:

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-cnb4v0

Out[2]=2

Compile a program that contains TypeOf:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-4oxtdl

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-n8ymoc

Out[2]=2

TypeOf is useful in polymorphic declarations written with ForAllType because the types of arguments are not known when the declaration is made:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-c08oz7

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-x973da

Out[2]=2

TypeOf can be used with TypeEvaluate to determine the type in a declaration:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-ikbkd

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-j8iobd

Out[2]=2

In[3]:=3

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https://wolfram.com/xid/0bimqnyw-gjld8g

Out[3]=3

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

Find the type of a program using arrays:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-w9cbsz

Out[1]=1

TypeOf does not evaluate its argument in compiled code, just as in evaluated code:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-mw79ym

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-ukri0f

Out[2]=2

Applications (1)Sample problems that can be solved with this function

Find the results of multiplying different types together:

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-up4ewr

In[3]:=3

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https://wolfram.com/xid/0bimqnyw-cy5qlv

Out[3]=3

Properties & Relations (3)Properties of the function, and connections to other functions

TypeOf infers the type of its input without evaluating it:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-ycghtp

Out[1]=1

TypeOf gives the return type of the CompiledCodeFunction generated by FunctionCompile but is much faster:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-vdua24

Out[1]=1

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-wdmdub

Out[2]=2

If TypeOf is unable to compile something, it issues a message that typically contains a button to show the source of the error:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-egst63

Out[1]=1

Clicking the source button typically opens a user interface that can help to locate the error:

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-3owia0

Possible Issues (3)Common pitfalls and unexpected behavior

TypeOf can only infer the types of compilable programs:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-b3g6ty

Out[1]=1

TypeOf does not evaluate its argument, which leads to unintended consequences:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-yv4f8v

Out[1]=1

The argument of TypeOf may need explicit evaluation:

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-xshzj

Out[2]=2

TypeOf only computes the type of its primary argument, so does not find errors in declarations:

In[1]:=1

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https://wolfram.com/xid/0bimqnyw-wf848n

Out[1]=1

FunctionCompile does a full compilation and can find errors in declarations:

In[2]:=2

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https://wolfram.com/xid/0bimqnyw-zgsgpm

Out[2]=2

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