Abstract syntax (Revised7.0 Report on the Algorithmic Language Scheme (Unofficial))

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7.2.1 Abstract syntax ¶

 $\begin{array}{l} K & \in & Con & constants, including quotations \\ I & \in & Ide & identifiers (variables) \\ E & \in & Exp & expressions \\ Γ & \in & Com = Exp & commands \end{array}$

 $Exp$  →  $K$  |  $I$  | ( $E_{0}$   $E^{*}$ )
     | (lambda ( $I^{*}$ )  $Γ^{*}$   $E_{0}$ )
     | (lambda ( $I^{*}$  .  $I$ )  $Γ^{*}$   $E_{0}$ )
     | (lambda  $I$   $Γ^{*}$   $E_{0}$ )
     | (if  $E_{0}$   $E_{1}$   $E_{2}$ ) | (if  $E_{0}$   $E_{1}$ )
     | (set!  $I$   $E$ )