The expr command transforms a string representing a valid Xcas statement into the actual statement.
| expr("a:=1") | 
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| a | 
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In particular, expr can transform a string representing a number into the number (see Section 3.1.1).
| expr("123") | 
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| expr("0123") | 
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since 0123 represents a base 8 integer (see Section 5.4.1) and 1· 82+2· 8+3=83.
| expr("0x12f") | 
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since 0x12f represents a base 16 number and 1· 162+2· 16+15=303.
| expr("123.4567") | 
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| expr("123e-5") | 
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